Best way to test if a row exists in a MySQL table
A COUNT query is faster, although maybe not noticeably, but as far as getting the desired result, both should be sufficient.
How do I choose grid and block dimensions for CUDA kernels?
The answers above point out how the block size can impact performance and suggest a common heuristic for its choice based on occupancy maximization. Without wanting to provide the criterion to choose the block size, it would be worth mentioning that CUDA 6.5 (now in Release Candidate version) includes several new runtime functions to aid in occupancy calculations and launch configuration, see
CUDA Pro Tip: Occupancy API Simplifies Launch Configuration
One of the useful functions is cudaOccupancyMaxPotentialBlockSize which heuristically calculates a block size that achieves the maximum occupancy. The values provided by that function could be then used as the starting point of a manual optimization of the launch parameters. Below is a little example.
#include <stdio.h>
/************************/
/* TEST KERNEL FUNCTION */
/************************/
__global__ void MyKernel(int *a, int *b, int *c, int N)
{
int idx = threadIdx.x + blockIdx.x * blockDim.x;
if (idx < N) { c[idx] = a[idx] + b[idx]; }
}
/********/
/* MAIN */
/********/
void main()
{
const int N = 1000000;
int blockSize; // The launch configurator returned block size
int minGridSize; // The minimum grid size needed to achieve the maximum occupancy for a full device launch
int gridSize; // The actual grid size needed, based on input size
int* h_vec1 = (int*) malloc(N*sizeof(int));
int* h_vec2 = (int*) malloc(N*sizeof(int));
int* h_vec3 = (int*) malloc(N*sizeof(int));
int* h_vec4 = (int*) malloc(N*sizeof(int));
int* d_vec1; cudaMalloc((void**)&d_vec1, N*sizeof(int));
int* d_vec2; cudaMalloc((void**)&d_vec2, N*sizeof(int));
int* d_vec3; cudaMalloc((void**)&d_vec3, N*sizeof(int));
for (int i=0; i<N; i++) {
h_vec1[i] = 10;
h_vec2[i] = 20;
h_vec4[i] = h_vec1[i] + h_vec2[i];
}
cudaMemcpy(d_vec1, h_vec1, N*sizeof(int), cudaMemcpyHostToDevice);
cudaMemcpy(d_vec2, h_vec2, N*sizeof(int), cudaMemcpyHostToDevice);
float time;
cudaEvent_t start, stop;
cudaEventCreate(&start);
cudaEventCreate(&stop);
cudaEventRecord(start, 0);
cudaOccupancyMaxPotentialBlockSize(&minGridSize, &blockSize, MyKernel, 0, N);
// Round up according to array size
gridSize = (N + blockSize - 1) / blockSize;
cudaEventRecord(stop, 0);
cudaEventSynchronize(stop);
cudaEventElapsedTime(&time, start, stop);
printf("Occupancy calculator elapsed time: %3.3f ms \n", time);
cudaEventRecord(start, 0);
MyKernel<<<gridSize, blockSize>>>(d_vec1, d_vec2, d_vec3, N);
cudaEventRecord(stop, 0);
cudaEventSynchronize(stop);
cudaEventElapsedTime(&time, start, stop);
printf("Kernel elapsed time: %3.3f ms \n", time);
printf("Blocksize %i\n", blockSize);
cudaMemcpy(h_vec3, d_vec3, N*sizeof(int), cudaMemcpyDeviceToHost);
for (int i=0; i<N; i++) {
if (h_vec3[i] != h_vec4[i]) { printf("Error at i = %i! Host = %i; Device = %i\n", i, h_vec4[i], h_vec3[i]); return; };
}
printf("Test passed\n");
}
EDIT
The cudaOccupancyMaxPotentialBlockSize is defined in the cuda_runtime.h file and is defined as follows:
template<class T>
__inline__ __host__ CUDART_DEVICE cudaError_t cudaOccupancyMaxPotentialBlockSize(
int *minGridSize,
int *blockSize,
T func,
size_t dynamicSMemSize = 0,
int blockSizeLimit = 0)
{
return cudaOccupancyMaxPotentialBlockSizeVariableSMem(minGridSize, blockSize, func, __cudaOccupancyB2DHelper(dynamicSMemSize), blockSizeLimit);
}
The meanings for the parameters is the following
minGridSize = Suggested min grid size to achieve a full machine launch.
blockSize = Suggested block size to achieve maximum occupancy.
func = Kernel function.
dynamicSMemSize = Size of dynamically allocated shared memory. Of course, it is known at runtime before any kernel launch. The size of the statically allocated shared memory is not needed as it is inferred by the properties of func.
blockSizeLimit = Maximum size for each block. In the case of 1D kernels, it can coincide with the number of input elements.
Note that, as of CUDA 6.5, one needs to compute one's own 2D/3D block dimensions from the 1D block size suggested by the API.
Note also that the CUDA driver API contains functionally equivalent APIs for occupancy calculation, so it is possible to use cuOccupancyMaxPotentialBlockSize in driver API code in the same way shown for the runtime API in the example above.
How to get object size in memory?
Unmanaged object:
Marshal.SizeOf(object yourObj);
Value Types:
sizeof(object val)
Managed object:
- Looks like there is no direct way to get for managed objects, Ref: https://devblogs.microsoft.com/cbrumme/size-of-a-managed-object/
Is there any advantage of using map over unordered_map in case of trivial keys?
Small addition to all of above:
Better use map, when you need to get elements by range, as they are sorted and you can just iterate over them from one boundary to another.
NTFS performance and large volumes of files and directories
100,000 should be fine.
I have (anecdotally) seen people having problems with many millions of files and I have had problems myself with Explorer just not having a clue how to count past 60-something thousand files, but NTFS should be good for the volumes you're talking.
In case you're wondering, the technical (and I hope theoretical) maximum number of files is: 4,294,967,295
Best way to stress test a website
JMeter would be one such tool. Can be a bit hard to learn and configure, but it's usually worth it.
Prepend text to beginning of string
If you want to use the version of Javascript called ES 2015 (aka ES6) or later, you can use template strings introduced by ES 2015 and recommended by some guidelines (like Airbnb's style guide):
const after = "test";
const mystr = `This is: ${after}`;
Is Python faster and lighter than C++?
The problem here is that you have two different languages that solve two different problems... its like comparing C++ with assembler.
Python is for rapid application development and for when performance is a minimal concern.
C++ is not for rapid application development and inherits a legacy of speed from C - for low level programming.
Performance of FOR vs FOREACH in PHP
It's 2020 and stuffs had greatly evolved with php 7.4 and opcache.
Here is the OP^ benchmark, ran as unix CLI, without the echo and html parts.
Test ran locally on a regular computer.
php -v
PHP 7.4.6 (cli) (built: May 14 2020 10:02:44) ( NTS )
Modified benchmark script:
<?php
## preperations; just a simple environment state
$test_iterations = 100;
$test_arr_size = 1000;
// a shared function that makes use of the loop; this should
// ensure no funny business is happening to fool the test
function test($input)
{
//echo '<!-- '.trim($input).' -->';
}
// for each test we create a array this should avoid any of the
// arrays internal representation or optimizations from getting
// in the way.
// normal array
$test_arr1 = array();
$test_arr2 = array();
$test_arr3 = array();
// hash tables
$test_arr4 = array();
$test_arr5 = array();
for ($i = 0; $i < $test_arr_size; ++$i)
{
mt_srand();
$hash = md5(mt_rand());
$key = substr($hash, 0, 5).$i;
$test_arr1[$i] = $test_arr2[$i] = $test_arr3[$i] = $test_arr4[$key] = $test_arr5[$key]
= $hash;
}
## foreach
$start = microtime(true);
for ($j = 0; $j < $test_iterations; ++$j)
{
foreach ($test_arr1 as $k => $v)
{
test($v);
}
}
echo 'foreach '.(microtime(true) - $start)."\n";
## foreach (using reference)
$start = microtime(true);
for ($j = 0; $j < $test_iterations; ++$j)
{
foreach ($test_arr2 as &$value)
{
test($value);
}
}
echo 'foreach (using reference) '.(microtime(true) - $start)."\n";
## for
$start = microtime(true);
for ($j = 0; $j < $test_iterations; ++$j)
{
$size = count($test_arr3);
for ($i = 0; $i < $size; ++$i)
{
test($test_arr3[$i]);
}
}
echo 'for '.(microtime(true) - $start)."\n";
## foreach (hash table)
$start = microtime(true);
for ($j = 0; $j < $test_iterations; ++$j)
{
foreach ($test_arr4 as $k => $v)
{
test($v);
}
}
echo 'foreach (hash table) '.(microtime(true) - $start)."\n";
## for (hash table)
$start = microtime(true);
for ($j = 0; $j < $test_iterations; ++$j)
{
$keys = array_keys($test_arr5);
$size = sizeOf($test_arr5);
for ($i = 0; $i < $size; ++$i)
{
test($test_arr5[$keys[$i]]);
}
}
echo 'for (hash table) '.(microtime(true) - $start)."\n";
Output:
foreach 0.0032877922058105
foreach (using reference) 0.0029420852661133
for 0.0025191307067871
foreach (hash table) 0.0035080909729004
for (hash table) 0.0061779022216797
As you can see the evolution is insane, about 560 time faster than reported in 2012.
On my machines and servers, following my numerous experiments, basics for loops are the fastest. This is even clearer using nested loops ($i $j $k..)
It is also the most flexible in usage, and has a better readability from my view.
Python vs Bash - In which kind of tasks each one outruns the other performance-wise?
There are 2 scenario's where Bash performance is at least equal I believe:
- Scripting of command line utilities
- Scripts which take only a short time to execute; where starting the Python interpreter takes more time than the operation itself
That said, I usually don't really concern myself with performance of the scripting language itself. If performance is a real issue you don't script but program (possibly in Python).
StringBuilder vs String concatenation in toString() in Java
I prefer:
String.format( "{a: %s, b: %s, c: %s}", a, b, c );
...because it's short and readable.
I would not optimize this for speed unless you use it inside a loop with a very high repeat count and have measured the performance difference.
I agree, that if you have to output a lot of parameters, this form can get confusing (like one of the comments say). In this case I'd switch to a more readable form (perhaps using ToStringBuilder of apache-commons - taken from the answer of matt b) and ignore performance again.
Efficient way to do batch INSERTS with JDBC
This is a mix of the two previous answers:
PreparedStatement ps = c.prepareStatement("INSERT INTO employees VALUES (?, ?)");
ps.setString(1, "John");
ps.setString(2,"Doe");
ps.addBatch();
ps.clearParameters();
ps.setString(1, "Dave");
ps.setString(2,"Smith");
ps.addBatch();
ps.clearParameters();
int[] results = ps.executeBatch();
What is the best way to paginate results in SQL Server
Getting the total number of results and paginating are two different operations. For the sake of this example, let's assume that the query you're dealing with is
SELECT * FROM Orders WHERE OrderDate >= '1980-01-01' ORDER BY OrderDate
In this case, you would determine the total number of results using:
SELECT COUNT(*) FROM Orders WHERE OrderDate >= '1980-01-01'
...which may seem inefficient, but is actually pretty performant, assuming all indexes etc. are properly set up.
Next, to get actual results back in a paged fashion, the following query would be most efficient:
SELECT *
FROM ( SELECT ROW_NUMBER() OVER ( ORDER BY OrderDate ) AS RowNum, *
FROM Orders
WHERE OrderDate >= '1980-01-01'
) AS RowConstrainedResult
WHERE RowNum >= 1
AND RowNum < 20
ORDER BY RowNum
This will return rows 1-19 of the original query. The cool thing here, especially for web apps, is that you don't have to keep any state, except the row numbers to be returned.
Counting the number of files in a directory using Java
Since you don't really need the total number, and in fact want to perform an action after a certain number (in your case 5000), you can use java.nio.file.Files.newDirectoryStream. The benefit is that you can exit early instead having to go through the entire directory just to get a count.
public boolean isOverMax(){
Path dir = Paths.get("C:/foo/bar");
int i = 1;
try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir)) {
for (Path p : stream) {
//larger than max files, exit
if (++i > MAX_FILES) {
return true;
}
}
} catch (IOException ex) {
ex.printStackTrace();
}
return false;
}
The interface doc for DirectoryStream also has some good examples.
How to clear APC cache entries?
If you want to monitor the results via json, you can use this kind of script:
<?php
$result1 = apc_clear_cache();
$result2 = apc_clear_cache('user');
$result3 = apc_clear_cache('opcode');
$infos = apc_cache_info();
$infos['apc_clear_cache'] = $result1;
$infos["apc_clear_cache('user')"] = $result2;
$infos["apc_clear_cache('opcode')"] = $result3;
$infos["success"] = $result1 && $result2 && $result3;
header('Content-type: application/json');
echo json_encode($infos);
As mentioned in other answers, this script will have to be called via http or curl and you will have to be secured if it is exposed in the web root of your application. (by ip, token...)
Is a LINQ statement faster than a 'foreach' loop?
I was interested in this question, so I did a test just now. Using .NET Framework 4.5.2 on an Intel(R) Core(TM) i3-2328M CPU @ 2.20GHz, 2200 Mhz, 2 Core(s) with 8GB ram running Microsoft Windows 7 Ultimate.
It looks like LINQ might be faster than for each loop. Here are the results I got:
Exists = True
Time = 174
Exists = True
Time = 149
It would be interesting if some of you could copy & paste this code in a console app and test as well. Before testing with an object (Employee) I tried the same test with integers. LINQ was faster there as well.
public class Program
{
public class Employee
{
public int id;
public string name;
public string lastname;
public DateTime dateOfBirth;
public Employee(int id,string name,string lastname,DateTime dateOfBirth)
{
this.id = id;
this.name = name;
this.lastname = lastname;
this.dateOfBirth = dateOfBirth;
}
}
public static void Main() => StartObjTest();
#region object test
public static void StartObjTest()
{
List<Employee> items = new List<Employee>();
for (int i = 0; i < 10000000; i++)
{
items.Add(new Employee(i,"name" + i,"lastname" + i,DateTime.Today));
}
Test3(items, items.Count-100);
Test4(items, items.Count - 100);
Console.Read();
}
public static void Test3(List<Employee> items, int idToCheck)
{
Stopwatch s = new Stopwatch();
s.Start();
bool exists = false;
foreach (var item in items)
{
if (item.id == idToCheck)
{
exists = true;
break;
}
}
Console.WriteLine("Exists=" + exists);
Console.WriteLine("Time=" + s.ElapsedMilliseconds);
}
public static void Test4(List<Employee> items, int idToCheck)
{
Stopwatch s = new Stopwatch();
s.Start();
bool exists = items.Exists(e => e.id == idToCheck);
Console.WriteLine("Exists=" + exists);
Console.WriteLine("Time=" + s.ElapsedMilliseconds);
}
#endregion
#region int test
public static void StartIntTest()
{
List<int> items = new List<int>();
for (int i = 0; i < 10000000; i++)
{
items.Add(i);
}
Test1(items, -100);
Test2(items, -100);
Console.Read();
}
public static void Test1(List<int> items,int itemToCheck)
{
Stopwatch s = new Stopwatch();
s.Start();
bool exists = false;
foreach (var item in items)
{
if (item == itemToCheck)
{
exists = true;
break;
}
}
Console.WriteLine("Exists=" + exists);
Console.WriteLine("Time=" + s.ElapsedMilliseconds);
}
public static void Test2(List<int> items, int itemToCheck)
{
Stopwatch s = new Stopwatch();
s.Start();
bool exists = items.Contains(itemToCheck);
Console.WriteLine("Exists=" + exists);
Console.WriteLine("Time=" + s.ElapsedMilliseconds);
}
#endregion
}
What is a "cache-friendly" code?
Preliminaries
On modern computers, only the lowest level memory structures (the registers) can move data around in single clock cycles. However, registers are very expensive and most computer cores have less than a few dozen registers. At the other end of the memory spectrum (DRAM), the memory is very cheap (i.e. literally millions of times cheaper) but takes hundreds of cycles after a request to receive the data. To bridge this gap between super fast and expensive and super slow and cheap are the cache memories, named L1, L2, L3 in decreasing speed and cost. The idea is that most of the executing code will be hitting a small set of variables often, and the rest (a much larger set of variables) infrequently. If the processor can't find the data in L1 cache, then it looks in L2 cache. If not there, then L3 cache, and if not there, main memory. Each of these "misses" is expensive in time.
(The analogy is cache memory is to system memory, as system memory is too hard disk storage. Hard disk storage is super cheap but very slow).
Caching is one of the main methods to reduce the impact of latency. To paraphrase Herb Sutter (cfr. links below): increasing bandwidth is easy, but we can't buy our way out of latency.
Data is always retrieved through the memory hierarchy (smallest == fastest to slowest). A cache hit/miss usually refers to a hit/miss in the highest level of cache in the CPU -- by highest level I mean the largest == slowest. The cache hit rate is crucial for performance since every cache miss results in fetching data from RAM (or worse ...) which takes a lot of time (hundreds of cycles for RAM, tens of millions of cycles for HDD). In comparison, reading data from the (highest level) cache typically takes only a handful of cycles.
In modern computer architectures, the performance bottleneck is leaving the CPU die (e.g. accessing RAM or higher). This will only get worse over time. The increase in processor frequency is currently no longer relevant to increase performance. The problem is memory access. Hardware design efforts in CPUs therefore currently focus heavily on optimizing caches, prefetching, pipelines and concurrency. For instance, modern CPUs spend around 85% of die on caches and up to 99% for storing/moving data!
There is quite a lot to be said on the subject. Here are a few great references about caches, memory hierarchies and proper programming:
- Agner Fog's page. In his excellent documents, you can find detailed examples covering languages ranging from assembly to C++.
- If you are into videos, I strongly recommend to have a look at Herb Sutter's talk on machine architecture (youtube) (specifically check 12:00 and onwards!).
- Slides about memory optimization by Christer Ericson (director of technology @ Sony)
- LWN.net's article "What every programmer should know about memory"
Main concepts for cache-friendly code
A very important aspect of cache-friendly code is all about the principle of locality, the goal of which is to place related data close in memory to allow efficient caching. In terms of the CPU cache, it's important to be aware of cache lines to understand how this works: How do cache lines work?
The following particular aspects are of high importance to optimize caching:
- Temporal locality: when a given memory location was accessed, it is likely that the same location is accessed again in the near future. Ideally, this information will still be cached at that point.
- Spatial locality: this refers to placing related data close to each other. Caching happens on many levels, not just in the CPU. For example, when you read from RAM, typically a larger chunk of memory is fetched than what was specifically asked for because very often the program will require that data soon. HDD caches follow the same line of thought. Specifically for CPU caches, the notion of cache lines is important.
Use appropriate c++ containers
A simple example of cache-friendly versus cache-unfriendly is c++'s std::vector versus std::list. Elements of a std::vector are stored in contiguous memory, and as such accessing them is much more cache-friendly than accessing elements in a std::list, which stores its content all over the place. This is due to spatial locality.
A very nice illustration of this is given by Bjarne Stroustrup in this youtube clip (thanks to @Mohammad Ali Baydoun for the link!).
Don't neglect the cache in data structure and algorithm design
Whenever possible, try to adapt your data structures and order of computations in a way that allows maximum use of the cache. A common technique in this regard is cache blocking (Archive.org version), which is of extreme importance in high-performance computing (cfr. for example ATLAS).
Know and exploit the implicit structure of data
Another simple example, which many people in the field sometimes forget is column-major (ex. fortran,matlab) vs. row-major ordering (ex. c,c++) for storing two dimensional arrays. For example, consider the following matrix:
1 2
3 4
In row-major ordering, this is stored in memory as 1 2 3 4; in column-major ordering, this would be stored as 1 3 2 4. It is easy to see that implementations which do not exploit this ordering will quickly run into (easily avoidable!) cache issues. Unfortunately, I see stuff like this very often in my domain (machine learning). @MatteoItalia showed this example in more detail in his answer.
When fetching a certain element of a matrix from memory, elements near it will be fetched as well and stored in a cache line. If the ordering is exploited, this will result in fewer memory accesses (because the next few values which are needed for subsequent computations are already in a cache line).
For simplicity, assume the cache comprises a single cache line which can contain 2 matrix elements and that when a given element is fetched from memory, the next one is too. Say we want to take the sum over all elements in the example 2x2 matrix above (lets call it M):
Exploiting the ordering (e.g. changing column index first in c++):
M[0][0] (memory) + M[0][1] (cached) + M[1][0] (memory) + M[1][1] (cached)
= 1 + 2 + 3 + 4
--> 2 cache hits, 2 memory accesses
Not exploiting the ordering (e.g. changing row index first in c++):
M[0][0] (memory) + M[1][0] (memory) + M[0][1] (memory) + M[1][1] (memory)
= 1 + 3 + 2 + 4
--> 0 cache hits, 4 memory accesses
In this simple example, exploiting the ordering approximately doubles execution speed (since memory access requires much more cycles than computing the sums). In practice, the performance difference can be much larger.
Avoid unpredictable branches
Modern architectures feature pipelines and compilers are becoming very good at reordering code to minimize delays due to memory access. When your critical code contains (unpredictable) branches, it is hard or impossible to prefetch data. This will indirectly lead to more cache misses.
This is explained very well here (thanks to @0x90 for the link): Why is processing a sorted array faster than processing an unsorted array?
Avoid virtual functions
In the context of c++, virtual methods represent a controversial issue with regard to cache misses (a general consensus exists that they should be avoided when possible in terms of performance). Virtual functions can induce cache misses during look up, but this only happens if the specific function is not called often (otherwise it would likely be cached), so this is regarded as a non-issue by some. For reference about this issue, check out: What is the performance cost of having a virtual method in a C++ class?
Common problems
A common problem in modern architectures with multiprocessor caches is called false sharing. This occurs when each individual processor is attempting to use data in another memory region and attempts to store it in the same cache line. This causes the cache line -- which contains data another processor can use -- to be overwritten again and again. Effectively, different threads make each other wait by inducing cache misses in this situation. See also (thanks to @Matt for the link): How and when to align to cache line size?
An extreme symptom of poor caching in RAM memory (which is probably not what you mean in this context) is so-called thrashing. This occurs when the process continuously generates page faults (e.g. accesses memory which is not in the current page) which require disk access.
Efficient way to update all rows in a table
update Hotels set Discount=30 where Hotelid >= 1 and Hotelid <= 5504
Fast query runs slow in SSRS
If your stored procedure uses linked servers or openquery, they may run quickly by themselves but take a long time to render in SSRS. Some general suggestions:
- Retrieve the data directly from the server where the data is stored by using a different data source instead of using the linked server to retrieve the data.
- Load the data from the remote server to a local table prior to executing the report, keeping the report query simple.
- Use a table variable to first retrieve the data from the remote server and then join with your local tables instead of directly returning a join with a linked server.
I see that the question has been answered, I'm just adding this in case someone has this same issue.
Best way to select random rows PostgreSQL
select * from table order by random() limit 1000;
If you know how many rows you want, check out tsm_system_rows.
tsm_system_rows
module provides the table sampling method SYSTEM_ROWS, which can be used in the TABLESAMPLE clause of a SELECT command.
This table sampling method accepts a single integer argument that is the maximum number of rows to read. The resulting sample will always contain exactly that many rows, unless the table does not contain enough rows, in which case the whole table is selected. Like the built-in SYSTEM sampling method, SYSTEM_ROWS performs block-level sampling, so that the sample is not completely random but may be subject to clustering effects, especially if only a small number of rows are requested.
First install the extension
CREATE EXTENSION tsm_system_rows;
Then your query,
SELECT *
FROM table
TABLESAMPLE SYSTEM_ROWS(1000);
Efficient evaluation of a function at every cell of a NumPy array
I believe I have found a better solution. The idea to change the function to python universal function (see documentation), which can exercise parallel computation under the hood.
One can write his own customised ufunc in C, which surely is more efficient, or by invoking np.frompyfunc, which is built-in factory method. After testing, this is more efficient than np.vectorize:
f = lambda x, y: x * y
f_arr = np.frompyfunc(f, 2, 1)
vf = np.vectorize(f)
arr = np.linspace(0, 1, 10000)
%timeit f_arr(arr, arr) # 307ms
%timeit f_arr(arr, arr) # 450ms
I have also tested larger samples, and the improvement is proportional. For comparison of performances of other methods, see this post
PHP Try and Catch for SQL Insert
Checking the documentation shows that its returns false on an error. So use the return status rather than or die(). It will return false if it fails, which you can log (or whatever you want to do) and then continue.
$rv = mysql_query("INSERT INTO redirects SET ua_string = '$ua_string'");
if ( $rv === false ){
//handle the error here
}
//page continues loading
Android studio takes too much memory
To reduce the lag i would recommend the follwing steps
my pc specs : 2 gb ram, processor: intel core2 duo
first kill all background process, if you have server or database running you could stop them first with following commands
sudo service apache2 stop
sudo service mysql stop
Then enable power saving mode in android studio by file>powersaving mode
It could disable background process, and then studio appears to go well
What's the best way to dedupe a table?
Here's the method I use if you can get your dupe criteria into a group by statement and your table has an id identity column for uniqueness:
delete t
from tablename t
inner join
(
select date_time, min(id) as min_id
from tablename
group by date_time
having count(*) > 1
) t2 on t.date_time = t2.date_time
where t.id > t2.min_id
In this example the date_time is the grouping criteria, if you have more than one column make sure to join on all of them.
Exact time measurement for performance testing
I'm using this:
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(myUrl);
System.Diagnostics.Stopwatch timer = new Stopwatch();
timer.Start();
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
statusCode = response.StatusCode.ToString();
response.Close();
timer.Stop();
Python vs. Java performance (runtime speed)
Different languages do different things with different levels of efficiency.
The Benchmarks Game has a whole load of different programming problems implemented in a lot of different languages.
How to count occurrences of a column value efficiently in SQL?
This should work:
SELECT age, count(age)
FROM Students
GROUP by age
If you need the id as well you could include the above as a sub query like so:
SELECT S.id, S.age, C.cnt
FROM Students S
INNER JOIN (SELECT age, count(age) as cnt
FROM Students
GROUP BY age) C ON S.age = C.age
How can you speed up Eclipse?
There is once more solution Delete all files from this two folders
.metadata.plugins\org.eclipse.core.resources.history .metadata.plugins\org.eclipse.jdt.core
This help for the first momment. But it still stay slow
Replacing a 32-bit loop counter with 64-bit introduces crazy performance deviations with _mm_popcnt_u64 on Intel CPUs
This is not an answer but a feedback with few compilers of 2021. On Intel CoffeeLake 9900k.
With Microsoft compiler (VS2019), toolset v142:
unsigned 209695540000 1.8322 sec 28.6152 GB/s uint64_t 209695540000 3.08764 sec 16.9802 GB/s
With Intel compiler 2021:
unsigned 209695540000 1.70845 sec 30.688 GB/s uint64_t 209695540000 1.57956 sec 33.1921 GB/s
According to Mysticial's answer, Intel compiler is aware of False Data Dependency, but not Microsoft compiler.
For intel compiler, I used /QxHost (optimize of CPU's architecture which is that of the host) /Oi (enable intrinsic functions) and #include <nmmintrin.h> instead of #include <immintrin.h>.
Full compile command: /GS /W3 /QxHost /Gy /Zi /O2 /D "NDEBUG" /D "_CONSOLE" /D "_UNICODE" /D "UNICODE" /Qipo /Zc:forScope /Oi /MD /Fa"x64\Release\" /EHsc /nologo /Fo"x64\Release\" //fprofile-instr-use "x64\Release\" /Fp"x64\Release\Benchmark.pch" .
The decompiled (by IDA 7.5) assembly from ICC:
int __cdecl main(int argc, const char **argv, const char **envp)
{
int v6; // er13
_BYTE *v8; // rsi
unsigned int v9; // edi
unsigned __int64 i; // rbx
unsigned __int64 v11; // rdi
int v12; // ebp
__int64 v13; // r14
__int64 v14; // rbx
unsigned int v15; // eax
unsigned __int64 v16; // rcx
unsigned int v17; // eax
unsigned __int64 v18; // rcx
__int64 v19; // rdx
unsigned int v20; // eax
int result; // eax
std::ostream *v23; // rbx
char v24; // dl
std::ostream *v33; // rbx
std::ostream *v41; // rbx
__int64 v42; // rdx
unsigned int v43; // eax
int v44; // ebp
__int64 v45; // r14
__int64 v46; // rbx
unsigned __int64 v47; // rax
unsigned __int64 v48; // rax
std::ostream *v50; // rdi
char v51; // dl
std::ostream *v58; // rdi
std::ostream *v60; // rdi
__int64 v61; // rdx
unsigned int v62; // eax
__asm
{
vmovdqa [rsp+98h+var_58], xmm8
vmovapd [rsp+98h+var_68], xmm7
vmovapd [rsp+98h+var_78], xmm6
}
if ( argc == 2 )
{
v6 = atol(argv[1]) << 20;
_R15 = v6;
v8 = operator new[](v6);
if ( v6 )
{
v9 = 1;
for ( i = 0i64; i < v6; i = v9++ )
v8[i] = rand();
}
v11 = (unsigned __int64)v6 >> 3;
v12 = 0;
v13 = Xtime_get_ticks_0();
v14 = 0i64;
do
{
if ( v6 )
{
v15 = 4;
v16 = 0i64;
do
{
v14 += __popcnt(*(_QWORD *)&v8[8 * v16])
+ __popcnt(*(_QWORD *)&v8[8 * v15 - 24])
+ __popcnt(*(_QWORD *)&v8[8 * v15 - 16])
+ __popcnt(*(_QWORD *)&v8[8 * v15 - 8]);
v16 = v15;
v15 += 4;
}
while ( v11 > v16 );
v17 = 4;
v18 = 0i64;
do
{
v14 += __popcnt(*(_QWORD *)&v8[8 * v18])
+ __popcnt(*(_QWORD *)&v8[8 * v17 - 24])
+ __popcnt(*(_QWORD *)&v8[8 * v17 - 16])
+ __popcnt(*(_QWORD *)&v8[8 * v17 - 8]);
v18 = v17;
v17 += 4;
}
while ( v11 > v18 );
}
v12 += 2;
}
while ( v12 != 10000 );
_RBP = 100 * (Xtime_get_ticks_0() - v13);
std::operator___std::char_traits_char___(std::cout, "unsigned\t");
v23 = (std::ostream *)std::ostream::operator<<(std::cout, v14);
std::operator___std::char_traits_char____0(v23, v24);
__asm
{
vmovq xmm0, rbp
vmovdqa xmm8, cs:__xmm@00000000000000004530000043300000
vpunpckldq xmm0, xmm0, xmm8
vmovapd xmm7, cs:__xmm@45300000000000004330000000000000
vsubpd xmm0, xmm0, xmm7
vpermilpd xmm1, xmm0, 1
vaddsd xmm6, xmm1, xmm0
vdivsd xmm1, xmm6, cs:__real@41cdcd6500000000
}
v33 = (std::ostream *)std::ostream::operator<<(v23);
std::operator___std::char_traits_char___(v33, " sec \t");
__asm
{
vmovq xmm0, r15
vpunpckldq xmm0, xmm0, xmm8
vsubpd xmm0, xmm0, xmm7
vpermilpd xmm1, xmm0, 1
vaddsd xmm0, xmm1, xmm0
vmulsd xmm7, xmm0, cs:__real@40c3880000000000
vdivsd xmm1, xmm7, xmm6
}
v41 = (std::ostream *)std::ostream::operator<<(v33);
std::operator___std::char_traits_char___(v41, " GB/s");
LOBYTE(v42) = 10;
v43 = std::ios::widen((char *)v41 + *(int *)(*(_QWORD *)v41 + 4i64), v42);
std::ostream::put(v41, v43);
std::ostream::flush(v41);
v44 = 0;
v45 = Xtime_get_ticks_0();
v46 = 0i64;
do
{
if ( v6 )
{
v47 = 0i64;
do
{
v46 += __popcnt(*(_QWORD *)&v8[8 * v47])
+ __popcnt(*(_QWORD *)&v8[8 * v47 + 8])
+ __popcnt(*(_QWORD *)&v8[8 * v47 + 16])
+ __popcnt(*(_QWORD *)&v8[8 * v47 + 24]);
v47 += 4i64;
}
while ( v47 < v11 );
v48 = 0i64;
do
{
v46 += __popcnt(*(_QWORD *)&v8[8 * v48])
+ __popcnt(*(_QWORD *)&v8[8 * v48 + 8])
+ __popcnt(*(_QWORD *)&v8[8 * v48 + 16])
+ __popcnt(*(_QWORD *)&v8[8 * v48 + 24]);
v48 += 4i64;
}
while ( v48 < v11 );
}
v44 += 2;
}
while ( v44 != 10000 );
_RBP = 100 * (Xtime_get_ticks_0() - v45);
std::operator___std::char_traits_char___(std::cout, "uint64_t\t");
v50 = (std::ostream *)std::ostream::operator<<(std::cout, v46);
std::operator___std::char_traits_char____0(v50, v51);
__asm
{
vmovq xmm0, rbp
vpunpckldq xmm0, xmm0, cs:__xmm@00000000000000004530000043300000
vsubpd xmm0, xmm0, cs:__xmm@45300000000000004330000000000000
vpermilpd xmm1, xmm0, 1
vaddsd xmm6, xmm1, xmm0
vdivsd xmm1, xmm6, cs:__real@41cdcd6500000000
}
v58 = (std::ostream *)std::ostream::operator<<(v50);
std::operator___std::char_traits_char___(v58, " sec \t");
__asm { vdivsd xmm1, xmm7, xmm6 }
v60 = (std::ostream *)std::ostream::operator<<(v58);
std::operator___std::char_traits_char___(v60, " GB/s");
LOBYTE(v61) = 10;
v62 = std::ios::widen((char *)v60 + *(int *)(*(_QWORD *)v60 + 4i64), v61);
std::ostream::put(v60, v62);
std::ostream::flush(v60);
free(v8);
result = 0;
}
else
{
std::operator___std::char_traits_char___(std::cerr, "usage: array_size in MB");
LOBYTE(v19) = 10;
v20 = std::ios::widen((char *)&std::cerr + *((int *)std::cerr + 1), v19);
std::ostream::put(std::cerr, v20);
std::ostream::flush(std::cerr);
result = -1;
}
__asm
{
vmovaps xmm6, [rsp+98h+var_78]
vmovaps xmm7, [rsp+98h+var_68]
vmovaps xmm8, [rsp+98h+var_58]
}
return result;
}
and disassembly of main:
.text:0140001000 .686p
.text:0140001000 .mmx
.text:0140001000 .model flat
.text:0140001000
.text:0140001000 ; ===========================================================================
.text:0140001000
.text:0140001000 ; Segment type: Pure code
.text:0140001000 ; Segment permissions: Read/Execute
.text:0140001000 _text segment para public 'CODE' use64
.text:0140001000 assume cs:_text
.text:0140001000 ;org 140001000h
.text:0140001000 assume es:nothing, ss:nothing, ds:_data, fs:nothing, gs:nothing
.text:0140001000
.text:0140001000 ; =============== S U B R O U T I N E =======================================
.text:0140001000
.text:0140001000
.text:0140001000 ; int __cdecl main(int argc, const char **argv, const char **envp)
.text:0140001000 main proc near ; CODE XREF: __scrt_common_main_seh+107?p
.text:0140001000 ; DATA XREF: .pdata:ExceptionDir?o
.text:0140001000
.text:0140001000 var_78 = xmmword ptr -78h
.text:0140001000 var_68 = xmmword ptr -68h
.text:0140001000 var_58 = xmmword ptr -58h
.text:0140001000
.text:0140001000 push r15
.text:0140001002 push r14
.text:0140001004 push r13
.text:0140001006 push r12
.text:0140001008 push rsi
.text:0140001009 push rdi
.text:014000100A push rbp
.text:014000100B push rbx
.text:014000100C sub rsp, 58h
.text:0140001010 vmovdqa [rsp+98h+var_58], xmm8
.text:0140001016 vmovapd [rsp+98h+var_68], xmm7
.text:014000101C vmovapd [rsp+98h+var_78], xmm6
.text:0140001022 cmp ecx, 2
.text:0140001025 jnz loc_14000113E
.text:014000102B mov rcx, [rdx+8] ; String
.text:014000102F call cs:__imp_atol
.text:0140001035 mov r13d, eax
.text:0140001038 shl r13d, 14h
.text:014000103C movsxd r15, r13d
.text:014000103F mov rcx, r15 ; size
.text:0140001042 call ??_U@YAPEAX_K@Z ; operator new[](unsigned __int64)
.text:0140001047 mov rsi, rax
.text:014000104A test r15d, r15d
.text:014000104D jz short loc_14000106E
.text:014000104F mov edi, 1
.text:0140001054 xor ebx, ebx
.text:0140001056 mov rbp, cs:__imp_rand
.text:014000105D nop dword ptr [rax]
.text:0140001060
.text:0140001060 loc_140001060: ; CODE XREF: main+6C?j
.text:0140001060 call rbp ; __imp_rand
.text:0140001062 mov [rsi+rbx], al
.text:0140001065 mov ebx, edi
.text:0140001067 inc edi
.text:0140001069 cmp rbx, r15
.text:014000106C jb short loc_140001060
.text:014000106E
.text:014000106E loc_14000106E: ; CODE XREF: main+4D?j
.text:014000106E mov rdi, r15
.text:0140001071 shr rdi, 3
.text:0140001075 xor ebp, ebp
.text:0140001077 call _Xtime_get_ticks_0
.text:014000107C mov r14, rax
.text:014000107F xor ebx, ebx
.text:0140001081 jmp short loc_14000109F
.text:0140001081 ; ---------------------------------------------------------------------------
.text:0140001083 align 10h
.text:0140001090
.text:0140001090 loc_140001090: ; CODE XREF: main+A2?j
.text:0140001090 ; main+EC?j ...
.text:0140001090 add ebp, 2
.text:0140001093 cmp ebp, 2710h
.text:0140001099 jz loc_140001184
.text:014000109F
.text:014000109F loc_14000109F: ; CODE XREF: main+81?j
.text:014000109F test r13d, r13d
.text:01400010A2 jz short loc_140001090
.text:01400010A4 mov eax, 4
.text:01400010A9 xor ecx, ecx
.text:01400010AB nop dword ptr [rax+rax+00h]
.text:01400010B0
.text:01400010B0 loc_1400010B0: ; CODE XREF: main+E7?j
.text:01400010B0 popcnt rcx, qword ptr [rsi+rcx*8]
.text:01400010B6 add rcx, rbx
.text:01400010B9 lea edx, [rax-3]
.text:01400010BC popcnt rdx, qword ptr [rsi+rdx*8]
.text:01400010C2 add rdx, rcx
.text:01400010C5 lea ecx, [rax-2]
.text:01400010C8 popcnt rcx, qword ptr [rsi+rcx*8]
.text:01400010CE add rcx, rdx
.text:01400010D1 lea edx, [rax-1]
.text:01400010D4 xor ebx, ebx
.text:01400010D6 popcnt rbx, qword ptr [rsi+rdx*8]
.text:01400010DC add rbx, rcx
.text:01400010DF mov ecx, eax
.text:01400010E1 add eax, 4
.text:01400010E4 cmp rdi, rcx
.text:01400010E7 ja short loc_1400010B0
.text:01400010E9 test r13d, r13d
.text:01400010EC jz short loc_140001090
.text:01400010EE mov eax, 4
.text:01400010F3 xor ecx, ecx
.text:01400010F5 db 2Eh
.text:01400010F5 nop word ptr [rax+rax+00000000h]
.text:01400010FF nop
.text:0140001100
.text:0140001100 loc_140001100: ; CODE XREF: main+137?j
.text:0140001100 popcnt rcx, qword ptr [rsi+rcx*8]
.text:0140001106 add rcx, rbx
.text:0140001109 lea edx, [rax-3]
.text:014000110C popcnt rdx, qword ptr [rsi+rdx*8]
.text:0140001112 add rdx, rcx
.text:0140001115 lea ecx, [rax-2]
.text:0140001118 popcnt rcx, qword ptr [rsi+rcx*8]
.text:014000111E add rcx, rdx
.text:0140001121 lea edx, [rax-1]
.text:0140001124 xor ebx, ebx
.text:0140001126 popcnt rbx, qword ptr [rsi+rdx*8]
.text:014000112C add rbx, rcx
.text:014000112F mov ecx, eax
.text:0140001131 add eax, 4
.text:0140001134 cmp rdi, rcx
.text:0140001137 ja short loc_140001100
.text:0140001139 jmp loc_140001090
.text:014000113E ; ---------------------------------------------------------------------------
.text:014000113E
.text:014000113E loc_14000113E: ; CODE XREF: main+25?j
.text:014000113E mov rsi, cs:__imp_?cerr@std@@3V?$basic_ostream@DU?$char_traits@D@std@@@1@A ; std::ostream std::cerr
.text:0140001145 lea rdx, aUsageArraySize ; "usage: array_size in MB"
.text:014000114C mov rcx, rsi ; std::ostream *
.text:014000114F call std__operator___std__char_traits_char___
.text:0140001154 mov rax, [rsi]
.text:0140001157 movsxd rcx, dword ptr [rax+4]
.text:014000115B add rcx, rsi
.text:014000115E mov dl, 0Ah
.text:0140001160 call cs:__imp_?widen@?$basic_ios@DU?$char_traits@D@std@@@std@@QEBADD@Z ; std::ios::widen(char)
.text:0140001166 mov rcx, rsi
.text:0140001169 mov edx, eax
.text:014000116B call cs:__imp_?put@?$basic_ostream@DU?$char_traits@D@std@@@std@@QEAAAEAV12@D@Z ; std::ostream::put(char)
.text:0140001171 mov rcx, rsi
.text:0140001174 call cs:__imp_?flush@?$basic_ostream@DU?$char_traits@D@std@@@std@@QEAAAEAV12@XZ ; std::ostream::flush(void)
.text:014000117A mov eax, 0FFFFFFFFh
.text:014000117F jmp loc_1400013E2
.text:0140001184 ; ---------------------------------------------------------------------------
.text:0140001184
.text:0140001184 loc_140001184: ; CODE XREF: main+99?j
.text:0140001184 call _Xtime_get_ticks_0
.text:0140001189 sub rax, r14
.text:014000118C imul rbp, rax, 64h ; 'd'
.text:0140001190 mov r14, cs:__imp_?cout@std@@3V?$basic_ostream@DU?$char_traits@D@std@@@1@A ; std::ostream std::cout
.text:0140001197 lea rdx, aUnsigned ; "unsigned\t"
.text:014000119E mov rcx, r14 ; std::ostream *
.text:01400011A1 call std__operator___std__char_traits_char___
.text:01400011A6 mov rcx, r14
.text:01400011A9 mov rdx, rbx
.text:01400011AC call cs:__imp_??6?$basic_ostream@DU?$char_traits@D@std@@@std@@QEAAAEAV01@_K@Z ; std::ostream::operator<<(unsigned __int64)
.text:01400011B2 mov rbx, rax
.text:01400011B5 mov rcx, rax ; std::ostream *
.text:01400011B8 call std__operator___std__char_traits_char____0
.text:01400011BD vmovq xmm0, rbp
.text:01400011C2 vmovdqa xmm8, cs:__xmm@00000000000000004530000043300000
.text:01400011CA vpunpckldq xmm0, xmm0, xmm8
.text:01400011CF vmovapd xmm7, cs:__xmm@45300000000000004330000000000000
.text:01400011D7 vsubpd xmm0, xmm0, xmm7
.text:01400011DB vpermilpd xmm1, xmm0, 1
.text:01400011E1 vaddsd xmm6, xmm1, xmm0
.text:01400011E5 vdivsd xmm1, xmm6, cs:__real@41cdcd6500000000
.text:01400011ED mov r12, cs:__imp_??6?$basic_ostream@DU?$char_traits@D@std@@@std@@QEAAAEAV01@N@Z ; std::ostream::operator<<(double)
.text:01400011F4 mov rcx, rbx
.text:01400011F7 call r12 ; std::ostream::operator<<(double) ; std::ostream::operator<<(double)
.text:01400011FA mov rbx, rax
.text:01400011FD lea rdx, aSec ; " sec \t"
.text:0140001204 mov rcx, rax ; std::ostream *
.text:0140001207 call std__operator___std__char_traits_char___
.text:014000120C vmovq xmm0, r15
.text:0140001211 vpunpckldq xmm0, xmm0, xmm8
.text:0140001216 vsubpd xmm0, xmm0, xmm7
.text:014000121A vpermilpd xmm1, xmm0, 1
.text:0140001220 vaddsd xmm0, xmm1, xmm0
.text:0140001224 vmulsd xmm7, xmm0, cs:__real@40c3880000000000
.text:014000122C vdivsd xmm1, xmm7, xmm6
.text:0140001230 mov rcx, rbx
.text:0140001233 call r12 ; std::ostream::operator<<(double) ; std::ostream::operator<<(double)
.text:0140001236 mov rbx, rax
.text:0140001239 lea rdx, aGbS ; " GB/s"
.text:0140001240 mov rcx, rax ; std::ostream *
.text:0140001243 call std__operator___std__char_traits_char___
.text:0140001248 mov rax, [rbx]
.text:014000124B movsxd rcx, dword ptr [rax+4]
.text:014000124F add rcx, rbx
.text:0140001252 mov dl, 0Ah
.text:0140001254 call cs:__imp_?widen@?$basic_ios@DU?$char_traits@D@std@@@std@@QEBADD@Z ; std::ios::widen(char)
.text:014000125A mov rcx, rbx
.text:014000125D mov edx, eax
.text:014000125F call cs:__imp_?put@?$basic_ostream@DU?$char_traits@D@std@@@std@@QEAAAEAV12@D@Z ; std::ostream::put(char)
.text:0140001265 mov rcx, rbx
.text:0140001268 call cs:__imp_?flush@?$basic_ostream@DU?$char_traits@D@std@@@std@@QEAAAEAV12@XZ ; std::ostream::flush(void)
.text:014000126E xor ebp, ebp
.text:0140001270 call _Xtime_get_ticks_0
.text:0140001275 mov r14, rax
.text:0140001278 xor ebx, ebx
.text:014000127A jmp short loc_14000128F
.text:014000127A ; ---------------------------------------------------------------------------
.text:014000127C align 20h
.text:0140001280
.text:0140001280 loc_140001280: ; CODE XREF: main+292?j
.text:0140001280 ; main+2DB?j ...
.text:0140001280 add ebp, 2
.text:0140001283 cmp ebp, 2710h
.text:0140001289 jz loc_14000131D
.text:014000128F
.text:014000128F loc_14000128F: ; CODE XREF: main+27A?j
.text:014000128F test r13d, r13d
.text:0140001292 jz short loc_140001280
.text:0140001294 xor eax, eax
.text:0140001296 db 2Eh
.text:0140001296 nop word ptr [rax+rax+00000000h]
.text:01400012A0
.text:01400012A0 loc_1400012A0: ; CODE XREF: main+2D6?j
.text:01400012A0 xor ecx, ecx
.text:01400012A2 popcnt rcx, qword ptr [rsi+rax*8]
.text:01400012A8 add rcx, rbx
.text:01400012AB xor edx, edx
.text:01400012AD popcnt rdx, qword ptr [rsi+rax*8+8]
.text:01400012B4 add rdx, rcx
.text:01400012B7 xor ecx, ecx
.text:01400012B9 popcnt rcx, qword ptr [rsi+rax*8+10h]
.text:01400012C0 add rcx, rdx
.text:01400012C3 xor ebx, ebx
.text:01400012C5 popcnt rbx, qword ptr [rsi+rax*8+18h]
.text:01400012CC add rbx, rcx
.text:01400012CF add rax, 4
.text:01400012D3 cmp rax, rdi
.text:01400012D6 jb short loc_1400012A0
.text:01400012D8 test r13d, r13d
.text:01400012DB jz short loc_140001280
.text:01400012DD xor eax, eax
.text:01400012DF nop
.text:01400012E0
.text:01400012E0 loc_1400012E0: ; CODE XREF: main+316?j
.text:01400012E0 xor ecx, ecx
.text:01400012E2 popcnt rcx, qword ptr [rsi+rax*8]
.text:01400012E8 add rcx, rbx
.text:01400012EB xor edx, edx
.text:01400012ED popcnt rdx, qword ptr [rsi+rax*8+8]
.text:01400012F4 add rdx, rcx
.text:01400012F7 xor ecx, ecx
.text:01400012F9 popcnt rcx, qword ptr [rsi+rax*8+10h]
.text:0140001300 add rcx, rdx
.text:0140001303 xor ebx, ebx
.text:0140001305 popcnt rbx, qword ptr [rsi+rax*8+18h]
.text:014000130C add rbx, rcx
.text:014000130F add rax, 4
.text:0140001313 cmp rax, rdi
.text:0140001316 jb short loc_1400012E0
.text:0140001318 jmp loc_140001280
.text:014000131D ; ---------------------------------------------------------------------------
.text:014000131D
.text:014000131D loc_14000131D: ; CODE XREF: main+289?j
.text:014000131D call _Xtime_get_ticks_0
.text:0140001322 sub rax, r14
.text:0140001325 imul rbp, rax, 64h ; 'd'
.text:0140001329 mov rdi, cs:__imp_?cout@std@@3V?$basic_ostream@DU?$char_traits@D@std@@@1@A ; std::ostream std::cout
.text:0140001330 lea rdx, aUint64T ; "uint64_t\t"
.text:0140001337 mov rcx, rdi ; std::ostream *
.text:014000133A call std__operator___std__char_traits_char___
.text:014000133F mov rcx, rdi
.text:0140001342 mov rdx, rbx
.text:0140001345 call cs:__imp_??6?$basic_ostream@DU?$char_traits@D@std@@@std@@QEAAAEAV01@_K@Z ; std::ostream::operator<<(unsigned __int64)
.text:014000134B mov rdi, rax
.text:014000134E mov rcx, rax ; std::ostream *
.text:0140001351 call std__operator___std__char_traits_char____0
.text:0140001356 vmovq xmm0, rbp
.text:014000135B vpunpckldq xmm0, xmm0, cs:__xmm@00000000000000004530000043300000
.text:0140001363 vsubpd xmm0, xmm0, cs:__xmm@45300000000000004330000000000000
.text:014000136B vpermilpd xmm1, xmm0, 1
.text:0140001371 vaddsd xmm6, xmm1, xmm0
.text:0140001375 vdivsd xmm1, xmm6, cs:__real@41cdcd6500000000
.text:014000137D mov rcx, rdi
.text:0140001380 call r12 ; std::ostream::operator<<(double) ; std::ostream::operator<<(double)
.text:0140001383 mov rdi, rax
.text:0140001386 lea rdx, aSec ; " sec \t"
.text:014000138D mov rcx, rax ; std::ostream *
.text:0140001390 call std__operator___std__char_traits_char___
.text:0140001395 vdivsd xmm1, xmm7, xmm6
.text:0140001399 mov rcx, rdi
.text:014000139C call r12 ; std::ostream::operator<<(double) ; std::ostream::operator<<(double)
.text:014000139F mov rdi, rax
.text:01400013A2 lea rdx, aGbS ; " GB/s"
.text:01400013A9 mov rcx, rax ; std::ostream *
.text:01400013AC call std__operator___std__char_traits_char___
.text:01400013B1 mov rax, [rdi]
.text:01400013B4 movsxd rcx, dword ptr [rax+4]
.text:01400013B8 add rcx, rdi
.text:01400013BB mov dl, 0Ah
.text:01400013BD call cs:__imp_?widen@?$basic_ios@DU?$char_traits@D@std@@@std@@QEBADD@Z ; std::ios::widen(char)
.text:01400013C3 mov rcx, rdi
.text:01400013C6 mov edx, eax
.text:01400013C8 call cs:__imp_?put@?$basic_ostream@DU?$char_traits@D@std@@@std@@QEAAAEAV12@D@Z ; std::ostream::put(char)
.text:01400013CE mov rcx, rdi
.text:01400013D1 call cs:__imp_?flush@?$basic_ostream@DU?$char_traits@D@std@@@std@@QEAAAEAV12@XZ ; std::ostream::flush(void)
.text:01400013D7 mov rcx, rsi ; Block
.text:01400013DA call cs:__imp_free
.text:01400013E0 xor eax, eax
.text:01400013E2
.text:01400013E2 loc_1400013E2: ; CODE XREF: main+17F?j
.text:01400013E2 vmovaps xmm6, [rsp+98h+var_78]
.text:01400013E8 vmovaps xmm7, [rsp+98h+var_68]
.text:01400013EE vmovaps xmm8, [rsp+98h+var_58]
.text:01400013F4 add rsp, 58h
.text:01400013F8 pop rbx
.text:01400013F9 pop rbp
.text:01400013FA pop rdi
.text:01400013FB pop rsi
.text:01400013FC pop r12
.text:01400013FE pop r13
.text:0140001400 pop r14
.text:0140001402 pop r15
.text:0140001404 retn
.text:0140001404 main endp
Coffee lake specification update "POPCNT instruction may take longer to execute than expected".
Making the Android emulator run faster
On this year google I/O (2011), Google demonstrated a faster emulator. The problem is not so much on the byte code between ARM and x86 but the software rendering performed by QEMU. They bypass the rendering of QEMU and send the rendering directly to an X server I believe. They showed a car game with really good performace and fps.
I wonder when that will be available for developers...
Why is MySQL InnoDB insert so slow?
InnoDB doesn't cope well with 'random' primary keys. Try a sequential key or auto-increment, and I believe you'll see better performance. Your 'real' key field could still be indexed, but for a bulk insert you might be better off dropping and recreating that index in one hit after the insert in complete. Would be interested to see your benchmarks for that!
Some related questions
Best timing method in C?
I use SDL_GetTicks from the SDL library.
Comparing two byte arrays in .NET
I have not seen many linq solutions here.
I am not sure of the performance implications, however I generally stick to linq as rule of thumb and then optimize later if necessary.
public bool CompareTwoArrays(byte[] array1, byte[] array2)
{
return !array1.Where((t, i) => t != array2[i]).Any();
}
Please do note this only works if they are the same size arrays. an extension could look like so
public bool CompareTwoArrays(byte[] array1, byte[] array2)
{
if (array1.Length != array2.Length) return false;
return !array1.Where((t, i) => t != array2[i]).Any();
}
SQL 'like' vs '=' performance
Maybe you are looking about Full Text Search.
In contrast to full-text search, the LIKE Transact-SQL predicate works on character patterns only. Also, you cannot use the LIKE predicate to query formatted binary data. Furthermore, a LIKE query against a large amount of unstructured text data is much slower than an equivalent full-text query against the same data. A LIKE query against millions of rows of text data can take minutes to return; whereas a full-text query can take only seconds or less against the same data, depending on the number of rows that are returned.
How can you profile a Python script?
I just developed my own profiler inspired from pypref_time:
https://github.com/modaresimr/auto_profiler
By adding a decorator it will show a tree of time-consuming functions
@Profiler(depth=4, on_disable=show)
Install by: pip install auto_profiler
Example
import time # line number 1
import random
from auto_profiler import Profiler, Tree
def f1():
mysleep(.6+random.random())
def mysleep(t):
time.sleep(t)
def fact(i):
f1()
if(i==1):
return 1
return i*fact(i-1)
def show(p):
print('Time [Hits * PerHit] Function name [Called from] [Function Location]\n'+\
'-----------------------------------------------------------------------')
print(Tree(p.root, threshold=0.5))
@Profiler(depth=4, on_disable=show)
def main():
for i in range(5):
f1()
fact(3)
if __name__ == '__main__':
main()
Example Output
Time [Hits * PerHit] Function name [Called from] [function location]
-----------------------------------------------------------------------
8.974s [1 * 8.974] main [auto-profiler/profiler.py:267] [/test/t2.py:30]
+-- 5.954s [5 * 1.191] f1 [/test/t2.py:34] [/test/t2.py:14]
¦ +-- 5.954s [5 * 1.191] mysleep [/test/t2.py:15] [/test/t2.py:17]
¦ +-- 5.954s [5 * 1.191] <time.sleep>
|
|
| # The rest is for the example recursive function call fact
+-- 3.020s [1 * 3.020] fact [/test/t2.py:36] [/test/t2.py:20]
+-- 0.849s [1 * 0.849] f1 [/test/t2.py:21] [/test/t2.py:14]
¦ +-- 0.849s [1 * 0.849] mysleep [/test/t2.py:15] [/test/t2.py:17]
¦ +-- 0.849s [1 * 0.849] <time.sleep>
+-- 2.171s [1 * 2.171] fact [/test/t2.py:24] [/test/t2.py:20]
+-- 1.552s [1 * 1.552] f1 [/test/t2.py:21] [/test/t2.py:14]
¦ +-- 1.552s [1 * 1.552] mysleep [/test/t2.py:15] [/test/t2.py:17]
+-- 0.619s [1 * 0.619] fact [/test/t2.py:24] [/test/t2.py:20]
+-- 0.619s [1 * 0.619] f1 [/test/t2.py:21] [/test/t2.py:14]
SQL Server SELECT LAST N Rows
Is "Id" indexed? If not, that's an important thing to do (I suspect it is already indexed).
Also, do you need to return ALL columns? You may be able to get a substantial improvement in speed if you only actually need a smaller subset of columns which can be FULLY catered for by the index on the ID column - e.g. if you have a NONCLUSTERED index on the Id column, with no other fields included in the index, then it would have to do a lookup on the clustered index to actually get the rest of the columns to return and that could be making up a lot of the cost of the query. If it's a CLUSTERED index, or a NONCLUSTERED index that includes all the other fields you want to return in the query, then you should be fine.
Count(*) vs Count(1) - SQL Server
There is no difference.
Reason:
Books on-line says "
COUNT ( { [ [ ALL | DISTINCT ] expression ] | * } )"
"1" is a non-null expression: so it's the same as COUNT(*).
The optimizer recognizes it for what it is: trivial.
The same as EXISTS (SELECT * ... or EXISTS (SELECT 1 ...
Example:
SELECT COUNT(1) FROM dbo.tab800krows
SELECT COUNT(1),FKID FROM dbo.tab800krows GROUP BY FKID
SELECT COUNT(*) FROM dbo.tab800krows
SELECT COUNT(*),FKID FROM dbo.tab800krows GROUP BY FKID
Same IO, same plan, the works
Edit, Aug 2011
Edit, Dec 2011
COUNT(*) is mentioned specifically in ANSI-92 (look for "Scalar expressions 125")
Case:
a) If COUNT(*) is specified, then the result is the cardinality of T.
That is, the ANSI standard recognizes it as bleeding obvious what you mean. COUNT(1) has been optimized out by RDBMS vendors because of this superstition. Otherwise it would be evaluated as per ANSI
b) Otherwise, let TX be the single-column table that is the result of applying the <value expression> to each row of T and eliminating null values. If one or more null values are eliminated, then a completion condition is raised: warning-
Is a view faster than a simple query?
Definitely a view is better than a nested query for SQL Server. Without knowing exactly why it is better (until I read Mark Brittingham's post), I had run some tests and experienced almost shocking performance improvements when using a view versus a nested query. After running each version of the query several hundred times in a row, the view version of the query completed in half the time. I'd say that's proof enough for me.
How to reduce the image size without losing quality in PHP
You can resize and then use imagejpeg()
Don't pass 100 as the quality for imagejpeg() - anything over 90 is generally overkill and just gets you a bigger JPEG. For a thumbnail, try 75 and work downwards until the quality/size tradeoff is acceptable.
imagejpeg($tn, $save, 75);
What is the difference between parseInt() and Number()?
Summary:
parseInt():
- Takes a string as a first argument, the radix (An integer which is the base of a numeral system e.g. decimal 10 or binary 2) as a second argument
- The function returns a integer number, if the first character cannot be converted to a number
NaNwill be returned. - If the
parseInt()function encounters a non numerical value, it will cut off the rest of input string and only parse the part until the non numerical value. - If the radix is
undefinedor 0, JS will assume the following:- If the input string begins with "0x" or "0X", the radix is 16 (hexadecimal), the remainder of the string is parsed into a number.
- If the input value begins with a 0 the radix can be either 8 (octal) or 10 (decimal). Which radix is chosen is depending on JS engine implementation.
ES5specifies that 10 should be used then. However, this is not supported by all browsers, therefore always specify radix if your numbers can begin with a 0. - If the input value begins with any number, the radix will be 10
Number():
- The
Number()constructor can convert any argument input into a number. If theNumber()constructor cannot convert the input into a number,NaNwill be returned. - The
Number()constructor can also handle hexadecimal number, they have to start with0x.
Example:
console.log(parseInt('0xF', 16)); // 15_x000D_
_x000D_
// z is no number, it will only evaluate 0xF, therefore 15 is logged_x000D_
console.log(parseInt('0xFz123', 16));_x000D_
_x000D_
// because the radix is 10, A is considered a letter not a number (like in Hexadecimal)_x000D_
// Therefore, A will be cut off the string and 10 is logged_x000D_
console.log(parseInt('10A', 10)); // 10_x000D_
_x000D_
// first character isnot a number, therefore parseInt will return NaN_x000D_
console.log(parseInt('a1213', 10));_x000D_
_x000D_
_x000D_
console.log('\n');_x000D_
_x000D_
_x000D_
// start with 0X, therefore Number will interpret it as a hexadecimal value_x000D_
console.log(Number('0x11'));_x000D_
_x000D_
// Cannot be converted to a number, NaN will be returned, notice that_x000D_
// the number constructor will not cut off a non number part like parseInt does_x000D_
console.log(Number('123A'));_x000D_
_x000D_
// scientific notation is allowed_x000D_
console.log(Number('152e-1')); // 15.21Why is the Android emulator so slow? How can we speed up the Android emulator?
Android emulator is dead slow. It takes 800MB memory while running. If you are on Windows, You can use Microsoft Android Emulator. It is superb, provides you functionalities more than Android Studio Emulator. And most important it is fast ( consumes 13MB only). It comes with Visual Studio 2015 Technical Preview. I am using it and happy with it. I downloaded and installed entire VS pack, I need to look how we can install VS Emulator only.
Visual Studio Emulator for Android
EDIT: Try https://www.visualstudio.com/vs/msft-android-emulator/
Which is faster: Stack allocation or Heap allocation
Stack allocation is a couple instructions whereas the fastest rtos heap allocator known to me (TLSF) uses on average on the order of 150 instructions. Also stack allocations don't require a lock because they use thread local storage which is another huge performance win. So stack allocations can be 2-3 orders of magnitude faster depending on how heavily multithreaded your environment is.
In general heap allocation is your last resort if you care about performance. A viable in-between option can be a fixed pool allocator which is also only a couple instructions and has very little per-allocation overhead so it's great for small fixed size objects. On the downside it only works with fixed size objects, is not inherently thread safe and has block fragmentation problems.
Using varchar(MAX) vs TEXT on SQL Server
For large text, the full text index is much faster. But you can full text index varchar(max)as well.
while-else-loop
I don't see why there is a encapsulation of a while...
Use
//Use the appropriate start and end...
for(int rowIndex = 0, e = 65536; i < e; ++i){
if(rowIndex >= dataColLinker.size()) {
dataColLinker.add(value);
} else {
dataColLinker.set(rowIndex, value);
}
}
C# Sort and OrderBy comparison
I just want to add that orderby is way more useful.
Why? Because I can do this:
Dim thisAccountBalances = account.DictOfBalances.Values.ToList
thisAccountBalances.ForEach(Sub(x) x.computeBalanceOtherFactors())
thisAccountBalances=thisAccountBalances.OrderBy(Function(x) x.TotalBalance).tolist
listOfBalances.AddRange(thisAccountBalances)
Why complicated comparer? Just sort based on a field. Here I am sorting based on TotalBalance.
Very easy.
I can't do that with sort. I wonder why. Do fine with orderBy.
As for speed it's always O(n).
Will using 'var' affect performance?
If the compiler can do automatic type inferencing, then there wont be any issue with performance. Both of these will generate same code
var x = new ClassA();
ClassA x = new ClassA();
however, if you are constructing the type dynamically (LINQ ...) then var is your only question and there is other mechanism to compare to in order to say what is the penalty.
CSS performance relative to translateZ(0)
I can attest to the fact that -webkit-transform: translate3d(0, 0, 0); will mess with the new position: -webkit-sticky; property. With a left drawer navigation pattern that I was working on, the hardware acceleration I wanted with the transform property was messing with the fixed positioning of my top nav bar. I turned off the transform and the positioning worked fine.
Luckily, I seem to have had hardware acceleration on already, because I had -webkit-font-smoothing: antialiased on the html element. I was testing this behavior in iOS7 and Android.
Make first letter of a string upper case (with maximum performance)
I think the below method is the best solution
class Program
{
static string UppercaseWords(string value)
{
char[] array = value.ToCharArray();
// Handle the first letter in the string.
if (array.Length >= 1)
{
if (char.IsLower(array[0]))
{
array[0] = char.ToUpper(array[0]);
}
}
// Scan through the letters, checking for spaces.
// ... Uppercase the lowercase letters following spaces.
for (int i = 1; i < array.Length; i++)
{
if (array[i - 1] == ' ')
{
if (char.IsLower(array[i]))
{
array[i] = char.ToUpper(array[i]);
}
}
}
return new string(array);
}
static void Main()
{
// Uppercase words in these strings.
const string value1 = "something in the way";
const string value2 = "dot net PERLS";
const string value3 = "String_two;three";
const string value4 = " sam";
// ... Compute the uppercase strings.
Console.WriteLine(UppercaseWords(value1));
Console.WriteLine(UppercaseWords(value2));
Console.WriteLine(UppercaseWords(value3));
Console.WriteLine(UppercaseWords(value4));
}
}
Output
Something In The Way
Dot Net PERLS
String_two;three
Sam
C++ performance vs. Java/C#
You should define "perform better than..". Well, I know, you asked about speed, but its not everything that counts.
- Do virtual machines perform more runtime overhead? Yes!
- Do they eat more working memory? Yes!
- Do they have higher startup costs (runtime initialization and JIT compiler) ? Yes!
- Do they require a huge library installed? Yes!
And so on, its biased, yes ;)
With C# and Java you pay a price for what you get (faster coding, automatic memory management, big library and so on). But you have not much room to haggle about the details: take the complete package or nothing.
Even if those languages can optimize some code to execute faster than compiled code, the whole approach is (IMHO) inefficient. Imagine driving every day 5 miles to your workplace, with a truck! Its comfortable, it feels good, you are safe (extreme crumple zone) and after you step on the gas for some time, it will even be as fast as a standard car! Why don't we all have a truck to drive to work? ;)
In C++ you get what you pay for, not more, not less.
Quoting Bjarne Stroustrup: "C++ is my favorite garbage collected language because it generates so little garbage" link text
Are loops really faster in reverse?
Using the prefix increment operator is somewhat faster. With the postfix, the compiler must retain the previous value as the result of the expression.
for (var i = 0; i < n; ++i) {
do_stuff();
}
A smart interpreter or compiler will see that the result of i++ is not used and not store the result of the expression, but not all js engines do.
Deleting objects from an ArrayList in Java
int sizepuede= listaoptionVO.size();
for (int i = 0; i < sizepuede; i++) {
if(listaoptionVO.get(i).getDescripcionRuc()==null){
listaoptionVO.remove(listaoptionVO.get(i));
i--;
sizepuede--;
}
}
edit: added indentation
What is the runtime performance cost of a Docker container?
Docker isn't virtualization, as such -- instead, it's an abstraction on top of the kernel's support for different process namespaces, device namespaces, etc.; one namespace isn't inherently more expensive or inefficient than another, so what actually makes Docker have a performance impact is a matter of what's actually in those namespaces.
Docker's choices in terms of how it configures namespaces for its containers have costs, but those costs are all directly associated with benefits -- you can give them up, but in doing so you also give up the associated benefit:
- Layered filesystems are expensive -- exactly what the costs are vary with each one (and Docker supports multiple backends), and with your usage patterns (merging multiple large directories, or merging a very deep set of filesystems will be particularly expensive), but they're not free. On the other hand, a great deal of Docker's functionality -- being able to build guests off other guests in a copy-on-write manner, and getting the storage advantages implicit in same -- ride on paying this cost.
- DNAT gets expensive at scale -- but gives you the benefit of being able to configure your guest's networking independently of your host's and have a convenient interface for forwarding only the ports you want between them. You can replace this with a bridge to a physical interface, but again, lose the benefit.
- Being able to run each software stack with its dependencies installed in the most convenient manner -- independent of the host's distro, libc, and other library versions -- is a great benefit, but needing to load shared libraries more than once (when their versions differ) has the cost you'd expect.
And so forth. How much these costs actually impact you in your environment -- with your network access patterns, your memory constraints, etc -- is an item for which it's difficult to provide a generic answer.
How to convert a huge list-of-vector to a matrix more efficiently?
This should be equivalent to your current code, only a lot faster:
output <- matrix(unlist(z), ncol = 10, byrow = TRUE)
Why shouldn't I use PyPy over CPython if PyPy is 6.3 times faster?
Q: If PyPy can solve these great challenges (speed, memory consumption, parallelism) in comparison to CPython, what are its weaknesses that are preventing wider adoption?
A: First, there is little evidence that the PyPy team can solve the speed problem in general. Long-term evidence is showing that PyPy runs certain Python codes slower than CPython and this drawback seems to be rooted very deeply in PyPy.
Secondly, the current version of PyPy consumes much more memory than CPython in a rather large set of cases. So PyPy didn't solve the memory consumption problem yet.
Whether PyPy solves the mentioned great challenges and will in general be faster, less memory hungry, and more friendly to parallelism than CPython is an open question that cannot be solved in the short term. Some people are betting that PyPy will never be able to offer a general solution enabling it to dominate CPython 2.7 and 3.3 in all cases.
If PyPy succeeds to be better than CPython in general, which is questionable, the main weakness affecting its wider adoption will be its compatibility with CPython. There also exist issues such as the fact that CPython runs on a wider range of CPUs and OSes, but these issues are much less important compared to PyPy's performance and CPython-compatibility goals.
Q: Why can't I do drop in replacement of CPython with PyPy now?
A: PyPy isn't 100% compatible with CPython because it isn't simulating CPython under the hood. Some programs may still depend on CPython's unique features that are absent in PyPy such as C bindings, C implementations of Python object&methods, or the incremental nature of CPython's garbage collector.
Which are more performant, CTE or temporary tables?
This is a really open ended question, and it all depends on how its being used and the type of temp table (Table variable or traditional table).
A traditional temp table stores the data in the temp DB, which does slow down the temp tables; however table variables do not.
How do I find out what is hammering my SQL Server?
You can find some useful query here:
Investigating the Cause of SQL Server High CPU
For me this helped a lot:
SELECT s.session_id,
r.status,
r.blocking_session_id 'Blk by',
r.wait_type,
wait_resource,
r.wait_time / (1000 * 60) 'Wait M',
r.cpu_time,
r.logical_reads,
r.reads,
r.writes,
r.total_elapsed_time / (1000 * 60) 'Elaps M',
Substring(st.TEXT,(r.statement_start_offset / 2) + 1,
((CASE r.statement_end_offset
WHEN -1
THEN Datalength(st.TEXT)
ELSE r.statement_end_offset
END - r.statement_start_offset) / 2) + 1) AS statement_text,
Coalesce(Quotename(Db_name(st.dbid)) + N'.' + Quotename(Object_schema_name(st.objectid, st.dbid)) + N'.' +
Quotename(Object_name(st.objectid, st.dbid)), '') AS command_text,
r.command,
s.login_name,
s.host_name,
s.program_name,
s.last_request_end_time,
s.login_time,
r.open_transaction_count
FROM sys.dm_exec_sessions AS s
JOIN sys.dm_exec_requests AS r
ON r.session_id = s.session_id
CROSS APPLY sys.Dm_exec_sql_text(r.sql_handle) AS st
WHERE r.session_id != @@SPID
ORDER BY r.cpu_time desc
In the fields of status, wait_type and cpu_time you can find the most cpu consuming task that is running right now.
System.currentTimeMillis() vs. new Date() vs. Calendar.getInstance().getTime()
Looking at the JDK, innermost constructor for Calendar.getInstance() has this:
public GregorianCalendar(TimeZone zone, Locale aLocale) {
super(zone, aLocale);
gdate = (BaseCalendar.Date) gcal.newCalendarDate(zone);
setTimeInMillis(System.currentTimeMillis());
}
so it already automatically does what you suggest. Date's default constructor holds this:
public Date() {
this(System.currentTimeMillis());
}
So there really isn't need to get system time specifically unless you want to do some math with it before creating your Calendar/Date object with it. Also I do have to recommend joda-time to use as replacement for Java's own calendar/date classes if your purpose is to work with date calculations a lot.
Java HashMap performance optimization / alternative
If the two byte arrays you mention is your entire key, the values are in the range 0-51, unique and the order within the a and b arrays is insignificant, my math tells me that there is only just about 26 million possible permutations and that you likely are trying to fill the map with values for all possible keys.
In this case, both filling and retrieving values from your data store would of course be much faster if you use an array instead of a HashMap and index it from 0 to 25989599.
What's the most efficient way to test two integer ranges for overlap?
Here's my version:
int xmin = min(x1,x2)
, xmax = max(x1,x2)
, ymin = min(y1,y2)
, ymax = max(y1,y2);
for (int i = xmin; i < xmax; ++i)
if (ymin <= i && i <= ymax)
return true;
return false;
Unless you're running some high-performance range-checker on billions of widely-spaced integers, our versions should perform similarly. My point is, this is micro-optimization.
Most efficient way to concatenate strings in JavaScript?
I did a quick test in both node and chrome and found in both cases += is faster:
var profile = func => {
var start = new Date();
for (var i = 0; i < 10000000; i++) func('test');
console.log(new Date() - start);
}
profile(x => "testtesttesttesttest");
profile(x => `${x}${x}${x}${x}${x}`);
profile(x => x + x + x + x + x );
profile(x => { var s = x; s += x; s += x; s += x; s += x; return s; });
profile(x => [x, x, x, x, x].join(""));
profile(x => { var a = [x]; a.push(x); a.push(x); a.push(x); a.push(x); return a.join(""); });
results in node: 7.0.10
- assignment: 8
- template literals: 524
- plus: 382
- plus equals: 379
- array join: 1476
- array push join: 1651
results from chrome 86.0.4240.198:
- assignment: 6
- template literals: 531
- plus: 406
- plus equals: 403
- array join: 1552
- array push join: 1813
How to create a new object instance from a Type
Compiled expression is best way! (for performance to repeatedly create instance in runtime).
static readonly Func<X> YCreator = Expression.Lambda<Func<X>>(
Expression.New(typeof(Y).GetConstructor(Type.EmptyTypes))
).Compile();
X x = YCreator();
Statistics (2012):
Iterations: 5000000
00:00:00.8481762, Activator.CreateInstance(string, string)
00:00:00.8416930, Activator.CreateInstance(type)
00:00:06.6236752, ConstructorInfo.Invoke
00:00:00.1776255, Compiled expression
00:00:00.0462197, new
Statistics (2015, .net 4.5, x64):
Iterations: 5000000
00:00:00.2659981, Activator.CreateInstance(string, string)
00:00:00.2603770, Activator.CreateInstance(type)
00:00:00.7478936, ConstructorInfo.Invoke
00:00:00.0700757, Compiled expression
00:00:00.0286710, new
Statistics (2015, .net 4.5, x86):
Iterations: 5000000
00:00:00.3541501, Activator.CreateInstance(string, string)
00:00:00.3686861, Activator.CreateInstance(type)
00:00:00.9492354, ConstructorInfo.Invoke
00:00:00.0719072, Compiled expression
00:00:00.0229387, new
Statistics (2017, LINQPad 5.22.02/x64/.NET 4.6):
Iterations: 5000000
No args
00:00:00.3897563, Activator.CreateInstance(string assemblyName, string typeName)
00:00:00.3500748, Activator.CreateInstance(Type type)
00:00:01.0100714, ConstructorInfo.Invoke
00:00:00.1375767, Compiled expression
00:00:00.1337920, Compiled expression (type)
00:00:00.0593664, new
Single arg
00:00:03.9300630, Activator.CreateInstance(Type type)
00:00:01.3881770, ConstructorInfo.Invoke
00:00:00.1425534, Compiled expression
00:00:00.0717409, new
Statistics (2019, x64/.NET 4.8):
Iterations: 5000000
No args
00:00:00.3287835, Activator.CreateInstance(string assemblyName, string typeName)
00:00:00.3122015, Activator.CreateInstance(Type type)
00:00:00.8035712, ConstructorInfo.Invoke
00:00:00.0692854, Compiled expression
00:00:00.0662223, Compiled expression (type)
00:00:00.0337862, new
Single arg
00:00:03.8081959, Activator.CreateInstance(Type type)
00:00:01.2507642, ConstructorInfo.Invoke
00:00:00.0671756, Compiled expression
00:00:00.0301489, new
Statistics (2019, x64/.NET Core 3.0):
Iterations: 5000000
No args
00:00:00.3226895, Activator.CreateInstance(string assemblyName, string typeName)
00:00:00.2786803, Activator.CreateInstance(Type type)
00:00:00.6183554, ConstructorInfo.Invoke
00:00:00.0483217, Compiled expression
00:00:00.0485119, Compiled expression (type)
00:00:00.0434534, new
Single arg
00:00:03.4389401, Activator.CreateInstance(Type type)
00:00:01.0803609, ConstructorInfo.Invoke
00:00:00.0554756, Compiled expression
00:00:00.0462232, new
Full code:
static X CreateY_New()
{
return new Y();
}
static X CreateY_New_Arg(int z)
{
return new Y(z);
}
static X CreateY_CreateInstance()
{
return (X)Activator.CreateInstance(typeof(Y));
}
static X CreateY_CreateInstance_String()
{
return (X)Activator.CreateInstance("Program", "Y").Unwrap();
}
static X CreateY_CreateInstance_Arg(int z)
{
return (X)Activator.CreateInstance(typeof(Y), new object[] { z, });
}
private static readonly System.Reflection.ConstructorInfo YConstructor =
typeof(Y).GetConstructor(Type.EmptyTypes);
private static readonly object[] Empty = new object[] { };
static X CreateY_Invoke()
{
return (X)YConstructor.Invoke(Empty);
}
private static readonly System.Reflection.ConstructorInfo YConstructor_Arg =
typeof(Y).GetConstructor(new[] { typeof(int), });
static X CreateY_Invoke_Arg(int z)
{
return (X)YConstructor_Arg.Invoke(new object[] { z, });
}
private static readonly Func<X> YCreator = Expression.Lambda<Func<X>>(
Expression.New(typeof(Y).GetConstructor(Type.EmptyTypes))
).Compile();
static X CreateY_CompiledExpression()
{
return YCreator();
}
private static readonly Func<X> YCreator_Type = Expression.Lambda<Func<X>>(
Expression.New(typeof(Y))
).Compile();
static X CreateY_CompiledExpression_Type()
{
return YCreator_Type();
}
private static readonly ParameterExpression YCreator_Arg_Param = Expression.Parameter(typeof(int), "z");
private static readonly Func<int, X> YCreator_Arg = Expression.Lambda<Func<int, X>>(
Expression.New(typeof(Y).GetConstructor(new[] { typeof(int), }), new[] { YCreator_Arg_Param, }),
YCreator_Arg_Param
).Compile();
static X CreateY_CompiledExpression_Arg(int z)
{
return YCreator_Arg(z);
}
static void Main(string[] args)
{
const int iterations = 5000000;
Console.WriteLine("Iterations: {0}", iterations);
Console.WriteLine("No args");
foreach (var creatorInfo in new[]
{
new {Name = "Activator.CreateInstance(string assemblyName, string typeName)", Creator = (Func<X>)CreateY_CreateInstance},
new {Name = "Activator.CreateInstance(Type type)", Creator = (Func<X>)CreateY_CreateInstance},
new {Name = "ConstructorInfo.Invoke", Creator = (Func<X>)CreateY_Invoke},
new {Name = "Compiled expression", Creator = (Func<X>)CreateY_CompiledExpression},
new {Name = "Compiled expression (type)", Creator = (Func<X>)CreateY_CompiledExpression_Type},
new {Name = "new", Creator = (Func<X>)CreateY_New},
})
{
var creator = creatorInfo.Creator;
var sum = 0;
for (var i = 0; i < 1000; i++)
sum += creator().Z;
var stopwatch = new Stopwatch();
stopwatch.Start();
for (var i = 0; i < iterations; ++i)
{
var x = creator();
sum += x.Z;
}
stopwatch.Stop();
Console.WriteLine("{0}, {1}", stopwatch.Elapsed, creatorInfo.Name);
}
Console.WriteLine("Single arg");
foreach (var creatorInfo in new[]
{
new {Name = "Activator.CreateInstance(Type type)", Creator = (Func<int, X>)CreateY_CreateInstance_Arg},
new {Name = "ConstructorInfo.Invoke", Creator = (Func<int, X>)CreateY_Invoke_Arg},
new {Name = "Compiled expression", Creator = (Func<int, X>)CreateY_CompiledExpression_Arg},
new {Name = "new", Creator = (Func<int, X>)CreateY_New_Arg},
})
{
var creator = creatorInfo.Creator;
var sum = 0;
for (var i = 0; i < 1000; i++)
sum += creator(i).Z;
var stopwatch = new Stopwatch();
stopwatch.Start();
for (var i = 0; i < iterations; ++i)
{
var x = creator(i);
sum += x.Z;
}
stopwatch.Stop();
Console.WriteLine("{0}, {1}", stopwatch.Elapsed, creatorInfo.Name);
}
}
public class X
{
public X() { }
public X(int z) { this.Z = z; }
public int Z;
}
public class Y : X
{
public Y() {}
public Y(int z) : base(z) {}
}
Is it better to use std::memcpy() or std::copy() in terms to performance?
Just a minor addition: The speed difference between memcpy() and std::copy() can vary quite a bit depending on if optimizations are enabled or disabled. With g++ 6.2.0 and without optimizations memcpy() clearly wins:
Benchmark Time CPU Iterations
---------------------------------------------------
bm_memcpy 17 ns 17 ns 40867738
bm_stdcopy 62 ns 62 ns 11176219
bm_stdcopy_n 72 ns 72 ns 9481749
When optimizations are enabled (-O3), everything looks pretty much the same again:
Benchmark Time CPU Iterations
---------------------------------------------------
bm_memcpy 3 ns 3 ns 274527617
bm_stdcopy 3 ns 3 ns 272663990
bm_stdcopy_n 3 ns 3 ns 274732792
The bigger the array the less noticeable the effect gets, but even at N=1000 memcpy() is about twice as fast when optimizations aren't enabled.
Source code (requires Google Benchmark):
#include <string.h>
#include <algorithm>
#include <vector>
#include <benchmark/benchmark.h>
constexpr int N = 10;
void bm_memcpy(benchmark::State& state)
{
std::vector<int> a(N);
std::vector<int> r(N);
while (state.KeepRunning())
{
memcpy(r.data(), a.data(), N * sizeof(int));
}
}
void bm_stdcopy(benchmark::State& state)
{
std::vector<int> a(N);
std::vector<int> r(N);
while (state.KeepRunning())
{
std::copy(a.begin(), a.end(), r.begin());
}
}
void bm_stdcopy_n(benchmark::State& state)
{
std::vector<int> a(N);
std::vector<int> r(N);
while (state.KeepRunning())
{
std::copy_n(a.begin(), N, r.begin());
}
}
BENCHMARK(bm_memcpy);
BENCHMARK(bm_stdcopy);
BENCHMARK(bm_stdcopy_n);
BENCHMARK_MAIN()
/* EOF */
Split a large dataframe into a list of data frames based on common value in column
You can just as easily access each element in the list using e.g. path[[1]]. You can't put a set of matrices into an atomic vector and access each element. A matrix is an atomic vector with dimension attributes. I would use the list structure returned by split, it's what it was designed for. Each list element can hold data of different types and sizes so it's very versatile and you can use *apply functions to further operate on each element in the list. Example below.
# For reproducibile data
set.seed(1)
# Make some data
userid <- rep(1:2,times=4)
data1 <- replicate(8 , paste( sample(letters , 3 ) , collapse = "" ) )
data2 <- sample(10,8)
df <- data.frame( userid , data1 , data2 )
# Split on userid
out <- split( df , f = df$userid )
#$`1`
# userid data1 data2
#1 1 gjn 3
#3 1 yqp 1
#5 1 rjs 6
#7 1 jtw 5
#$`2`
# userid data1 data2
#2 2 xfv 4
#4 2 bfe 10
#6 2 mrx 2
#8 2 fqd 9
Access each element using the [[ operator like this:
out[[1]]
# userid data1 data2
#1 1 gjn 3
#3 1 yqp 1
#5 1 rjs 6
#7 1 jtw 5
Or use an *apply function to do further operations on each list element. For instance, to take the mean of the data2 column you could use sapply like this:
sapply( out , function(x) mean( x$data2 ) )
# 1 2
#3.75 6.25
Which method performs better: .Any() vs .Count() > 0?
About the Count() method, if the IEnumarable is an ICollection, then we can't iterate across all items because we can retrieve the Count field of ICollection, if the IEnumerable is not an ICollection we must iterate across all items using a while with a MoveNext, take a look the .NET Framework Code:
public static int Count<TSource>(this IEnumerable<TSource> source)
{
if (source == null)
throw Error.ArgumentNull("source");
ICollection<TSource> collectionoft = source as ICollection<TSource>;
if (collectionoft != null)
return collectionoft.Count;
ICollection collection = source as ICollection;
if (collection != null)
return collection.Count;
int count = 0;
using (IEnumerator<TSource> e = source.GetEnumerator())
{
checked
{
while (e.MoveNext()) count++;
}
}
return count;
}
Reference: Reference Source Enumerable
String formatting: % vs. .format vs. string literal
As I discovered today, the old way of formatting strings via % doesn't support Decimal, Python's module for decimal fixed point and floating point arithmetic, out of the box.
Example (using Python 3.3.5):
#!/usr/bin/env python3
from decimal import *
getcontext().prec = 50
d = Decimal('3.12375239e-24') # no magic number, I rather produced it by banging my head on my keyboard
print('%.50f' % d)
print('{0:.50f}'.format(d))
Output:
0.00000000000000000000000312375239000000009907464850 0.00000000000000000000000312375239000000000000000000
There surely might be work-arounds but you still might consider using the format() method right away.
Preferred method to store PHP arrays (json_encode vs serialize)
You might also be interested in https://github.com/phadej/igbinary - which provides a different serialization 'engine' for PHP.
My random/arbitrary 'performance' figures, using PHP 5.3.5 on a 64bit platform show :
JSON :
- JSON encoded in 2.180496931076 seconds
- JSON decoded in 9.8368630409241 seconds
- serialized "String" size : 13993
Native PHP :
- PHP serialized in 2.9125759601593 seconds
- PHP unserialized in 6.4348418712616 seconds
- serialized "String" size : 20769
Igbinary :
- WIN igbinary serialized in 1.6099879741669 seconds
- WIN igbinrary unserialized in 4.7737920284271 seconds
- WIN serialized "String" Size : 4467
So, it's quicker to igbinary_serialize() and igbinary_unserialize() and uses less disk space.
I used the fillArray(0, 3) code as above, but made the array keys longer strings.
igbinary can store the same data types as PHP's native serialize can (So no problem with objects etc) and you can tell PHP5.3 to use it for session handling if you so wish.
See also http://ilia.ws/files/zendcon_2010_hidden_features.pdf - specifically slides 14/15/16
Apache Spark: map vs mapPartitions?
Map:
Map transformation.
The map works on a single Row at a time.
Map returns after each input Row.
The map doesn’t hold the output result in Memory.
Map no way to figure out then to end the service.
// map example
val dfList = (1 to 100) toList
val df = dfList.toDF()
val dfInt = df.map(x => x.getInt(0)+2)
display(dfInt)
MapPartition:
MapPartition transformation.
MapPartition works on a partition at a time.
MapPartition returns after processing all the rows in the partition.
MapPartition output is retained in memory, as it can return after processing all the rows in a particular partition.
MapPartition service can be shut down before returning.
// MapPartition example
Val dfList = (1 to 100) toList
Val df = dfList.toDF()
Val df1 = df.repartition(4).rdd.mapPartition((int) => Iterator(itr.length))
Df1.collec()
//display(df1.collect())
For more details, please refer to the Spark map vs mapPartitions transformation article.
Hope this is helpful!
MySQL my.cnf performance tuning recommendations
I tried this tool and it gave me good results.
Why is printing "B" dramatically slower than printing "#"?
Yes the culprit is definitely word-wrapping. When I tested your two programs, NetBeans IDE 8.2 gave me the following result.
- First Matrix: O and # = 6.03 seconds
- Second Matrix: O and B = 50.97 seconds
Looking at your code closely you have used a line break at the end of first loop. But you didn't use any line break in second loop. So you are going to print a word with 1000 characters in the second loop. That causes a word-wrapping problem. If we use a non-word character " " after B, it takes only 5.35 seconds to compile the program. And If we use a line break in the second loop after passing 100 values or 50 values, it takes only 8.56 seconds and 7.05 seconds respectively.
Random r = new Random();
for (int i = 0; i < 1000; i++) {
for (int j = 0; j < 1000; j++) {
if(r.nextInt(4) == 0) {
System.out.print("O");
} else {
System.out.print("B");
}
if(j%100==0){ //Adding a line break in second loop
System.out.println();
}
}
System.out.println("");
}
Another advice is that to change settings of NetBeans IDE. First of all, go to NetBeans Tools and click Options. After that click Editor and go to Formatting tab. Then select Anywhere in Line Wrap Option. It will take almost 6.24% less time to compile the program.
Find the least number of coins required that can make any change from 1 to 99 cents
Here's my take. One Interesting thing is that we need to check min coins needed to form up to coin_with_max_value(25 in our case) - 1 only. After that just calculate the sum of these min coins. From that point we just need to add certain number of coin_with_max_value, to form any number up to the total cost, depending on the difference of total cost and the sum found out. That's it.
So for values we have take, once min coins for 24 is found out: [1, 2, 2, 5, 10, 10].
We just need to keep adding a 25 coin for every 25 values exceeding 30(sum of min coins).
Final answer for 99 is:
[1, 2, 2, 5, 10, 10, 25, 25, 25]
9
import itertools
import math
def ByCurrentCoins(val, coins):
for i in range(1, len(coins) + 1):
combinations = itertools.combinations(coins, i)
for combination in combinations:
if sum(combination) == val:
return True
return False
def ExtraCoin(val, all_coins, curr_coins):
for c in all_coins:
if ByCurrentCoins(val, curr_coins + [c]):
return c
def main():
cost = 99
coins = sorted([1, 2, 5, 10, 25], reverse=True)
max_coin = coins[0]
curr_coins = []
for c in range(1, min(max_coin, cost+1)):
if ByCurrentCoins(c, curr_coins):
continue
extra_coin = ExtraCoin(c, coins, curr_coins)
if not extra_coin:
print -1
return
curr_coins.append(extra_coin)
curr_sum = sum(curr_coins)
if cost > curr_sum:
extra_max_coins = int(math.ceil((cost - curr_sum)/float(max_coin)))
curr_coins.extend([max_coin for _ in range(extra_max_coins)])
print curr_coins
print len(curr_coins)
The most efficient way to remove first N elements in a list?
Python lists were not made to operate on the beginning of the list and are very ineffective at this operation.
While you can write
mylist = [1, 2 ,3 ,4]
mylist.pop(0)
It's very inefficient.
If you only want to delete items from your list, you can do this with del:
del mylist[:n]
Which is also really fast:
In [34]: %%timeit
help=range(10000)
while help:
del help[:1000]
....:
10000 loops, best of 3: 161 µs per loop
If you need to obtain elements from the beginning of the list, you should use collections.deque by Raymond Hettinger and its popleft() method.
from collections import deque
deque(['f', 'g', 'h', 'i', 'j'])
>>> d.pop() # return and remove the rightmost item
'j'
>>> d.popleft() # return and remove the leftmost item
'f'
A comparison:
list + pop(0)
In [30]: %%timeit
....: help=range(10000)
....: while help:
....: help.pop(0)
....:
100 loops, best of 3: 17.9 ms per loop
deque + popleft()
In [33]: %%timeit
help=deque(range(10000))
while help:
help.popleft()
....:
1000 loops, best of 3: 812 µs per loop
Fastest way to check a string is alphanumeric in Java
I've written the tests that compare using regular expressions (as per other answers) against not using regular expressions. Tests done on a quad core OSX10.8 machine running Java 1.6
Interestingly using regular expressions turns out to be about 5-10 times slower than manually iterating over a string. Furthermore the isAlphanumeric2() function is marginally faster than isAlphanumeric(). One supports the case where extended Unicode numbers are allowed, and the other is for when only standard ASCII numbers are allowed.
public class QuickTest extends TestCase {
private final int reps = 1000000;
public void testRegexp() {
for(int i = 0; i < reps; i++)
("ab4r3rgf"+i).matches("[a-zA-Z0-9]");
}
public void testIsAlphanumeric() {
for(int i = 0; i < reps; i++)
isAlphanumeric("ab4r3rgf"+i);
}
public void testIsAlphanumeric2() {
for(int i = 0; i < reps; i++)
isAlphanumeric2("ab4r3rgf"+i);
}
public boolean isAlphanumeric(String str) {
for (int i=0; i<str.length(); i++) {
char c = str.charAt(i);
if (!Character.isLetterOrDigit(c))
return false;
}
return true;
}
public boolean isAlphanumeric2(String str) {
for (int i=0; i<str.length(); i++) {
char c = str.charAt(i);
if (c < 0x30 || (c >= 0x3a && c <= 0x40) || (c > 0x5a && c <= 0x60) || c > 0x7a)
return false;
}
return true;
}
}
How do I speed up the gwt compiler?
Let's start with the uncomfortable truth: GWT compiler performance is really lousy. You can use some hacks here and there, but you're not going to get significantly better performance.
A nice performance hack you can do is to compile for only specific browsers, by inserting the following line in your gwt.xml:
<define-property name="user.agent" values="ie6,gecko,gecko1_8"></define-property>
or in gwt 2.x syntax, and for one browser only:
<set-property name="user.agent" value="gecko1_8"/>
This, for example, will compile your application for IE and FF only. If you know you are using only a specific browser for testing, you can use this little hack.
Another option: if you are using several locales, and again using only one for testing, you can comment them all out so that GWT will use the default locale, this shaves off some additional overhead from compile time.
Bottom line: you're not going to get order-of-magnitude increase in compiler performance, but taking several relaxations, you can shave off a few minutes here and there.
How can I increase the cursor speed in terminal?
If by "cursor speed", you mean the repeat rate when holding down a key - then have a look here: http://hints.macworld.com/article.php?story=20090823193018149
To summarize, open up a Terminal window and type the following command:
defaults write NSGlobalDomain KeyRepeat -int 0
More detail from the article:
Everybody knows that you can get a pretty fast keyboard repeat rate by changing a slider on the Keyboard tab of the Keyboard & Mouse System Preferences panel. But you can make it even faster! In Terminal, run this command:
defaults write NSGlobalDomain KeyRepeat -int 0
Then log out and log in again. The fastest setting obtainable via System Preferences is 2 (lower numbers are faster), so you may also want to try a value of 1 if 0 seems too fast. You can always visit the Keyboard & Mouse System Preferences panel to undo your changes.
You may find that a few applications don't handle extremely fast keyboard input very well, but most will do just fine with it.
What's the best way to convert a number to a string in JavaScript?
It seems similar results when using node.js. I ran this script:
let bar;
let foo = ["45","foo"];
console.time('string concat testing');
for (let i = 0; i < 10000000; i++) {
bar = "" + foo;
}
console.timeEnd('string concat testing');
console.time("string obj testing");
for (let i = 0; i < 10000000; i++) {
bar = String(foo);
}
console.timeEnd("string obj testing");
console.time("string both");
for (let i = 0; i < 10000000; i++) {
bar = "" + foo + "";
}
console.timeEnd("string both");
and got the following results:
? node testing.js
string concat testing: 2802.542ms
string obj testing: 3374.530ms
string both: 2660.023ms
Similar times each time I ran it.
Big O, how do you calculate/approximate it?
If you want to estimate the order of your code empirically rather than by analyzing the code, you could stick in a series of increasing values of n and time your code. Plot your timings on a log scale. If the code is O(x^n), the values should fall on a line of slope n.
This has several advantages over just studying the code. For one thing, you can see whether you're in the range where the run time approaches its asymptotic order. Also, you may find that some code that you thought was order O(x) is really order O(x^2), for example, because of time spent in library calls.
Speed comparison with Project Euler: C vs Python vs Erlang vs Haskell
With Haskell, you really don't need to think in recursions explicitly.
factorCount number = foldr factorCount' 0 [1..isquare] -
(fromEnum $ square == fromIntegral isquare)
where
square = sqrt $ fromIntegral number
isquare = floor square
factorCount' candidate
| number `rem` candidate == 0 = (2 +)
| otherwise = id
triangles :: [Int]
triangles = scanl1 (+) [1,2..]
main = print . head $ dropWhile ((< 1001) . factorCount) triangles
In the above code, I have replaced explicit recursions in @Thomas' answer with common list operations. The code still does exactly the same thing without us worrying about tail recursion. It runs (~ 7.49s) about 6% slower than the version in @Thomas' answer (~ 7.04s) on my machine with GHC 7.6.2, while the C version from @Raedwulf runs ~ 3.15s. It seems GHC has improved over the year.
PS. I know it is an old question, and I stumble upon it from google searches (I forgot what I was searching, now...). Just wanted to comment on the question about LCO and express my feelings about Haskell in general. I wanted to comment on the top answer, but comments do not allow code blocks.
SQL JOIN vs IN performance?
A interesting writeup on the logical differences: SQL Server: JOIN vs IN vs EXISTS - the logical difference
I am pretty sure that assuming that the relations and indexes are maintained a Join will perform better overall (more effort goes into working with that operation then others). If you think about it conceptually then its the difference between 2 queries and 1 query.
You need to hook it up to the Query Analyzer and try it and see the difference. Also look at the Query Execution Plan and try to minimize steps.
Increasing Heap Size on Linux Machines
You can use the following code snippet :
java -XX:+PrintFlagsFinal -Xms512m -Xmx1024m -Xss512k -XX:PermSize=64m -XX:MaxPermSize=128m
-version | grep -iE 'HeapSize|PermSize|ThreadStackSize'
In my pc I am getting following output :
uintx InitialHeapSize := 536870912 {product}
uintx MaxHeapSize := 1073741824 {product}
uintx PermSize := 67108864 {pd product}
uintx MaxPermSize := 134217728 {pd product}
intx ThreadStackSize := 512 {pd product}
pandas loc vs. iloc vs. at vs. iat?
There are two primary ways that pandas makes selections from a DataFrame.
- By Label
- By Integer Location
The documentation uses the term position for referring to integer location. I do not like this terminology as I feel it is confusing. Integer location is more descriptive and is exactly what .iloc stands for. The key word here is INTEGER - you must use integers when selecting by integer location.
Before showing the summary let's all make sure that ...
.ix is deprecated and ambiguous and should never be used
There are three primary indexers for pandas. We have the indexing operator itself (the brackets []), .loc, and .iloc. Let's summarize them:
[]- Primarily selects subsets of columns, but can select rows as well. Cannot simultaneously select rows and columns..loc- selects subsets of rows and columns by label only.iloc- selects subsets of rows and columns by integer location only
I almost never use .at or .iat as they add no additional functionality and with just a small performance increase. I would discourage their use unless you have a very time-sensitive application. Regardless, we have their summary:
.atselects a single scalar value in the DataFrame by label only.iatselects a single scalar value in the DataFrame by integer location only
In addition to selection by label and integer location, boolean selection also known as boolean indexing exists.
Examples explaining .loc, .iloc, boolean selection and .at and .iat are shown below
We will first focus on the differences between .loc and .iloc. Before we talk about the differences, it is important to understand that DataFrames have labels that help identify each column and each row. Let's take a look at a sample DataFrame:
df = pd.DataFrame({'age':[30, 2, 12, 4, 32, 33, 69],
'color':['blue', 'green', 'red', 'white', 'gray', 'black', 'red'],
'food':['Steak', 'Lamb', 'Mango', 'Apple', 'Cheese', 'Melon', 'Beans'],
'height':[165, 70, 120, 80, 180, 172, 150],
'score':[4.6, 8.3, 9.0, 3.3, 1.8, 9.5, 2.2],
'state':['NY', 'TX', 'FL', 'AL', 'AK', 'TX', 'TX']
},
index=['Jane', 'Nick', 'Aaron', 'Penelope', 'Dean', 'Christina', 'Cornelia'])
All the words in bold are the labels. The labels, age, color, food, height, score and state are used for the columns. The other labels, Jane, Nick, Aaron, Penelope, Dean, Christina, Cornelia are used as labels for the rows. Collectively, these row labels are known as the index.
The primary ways to select particular rows in a DataFrame are with the .loc and .iloc indexers. Each of these indexers can also be used to simultaneously select columns but it is easier to just focus on rows for now. Also, each of the indexers use a set of brackets that immediately follow their name to make their selections.
.loc selects data only by labels
We will first talk about the .loc indexer which only selects data by the index or column labels. In our sample DataFrame, we have provided meaningful names as values for the index. Many DataFrames will not have any meaningful names and will instead, default to just the integers from 0 to n-1, where n is the length(number of rows) of the DataFrame.
There are many different inputs you can use for .loc three out of them are
- A string
- A list of strings
- Slice notation using strings as the start and stop values
Selecting a single row with .loc with a string
To select a single row of data, place the index label inside of the brackets following .loc.
df.loc['Penelope']
This returns the row of data as a Series
age 4
color white
food Apple
height 80
score 3.3
state AL
Name: Penelope, dtype: object
Selecting multiple rows with .loc with a list of strings
df.loc[['Cornelia', 'Jane', 'Dean']]
This returns a DataFrame with the rows in the order specified in the list:
Selecting multiple rows with .loc with slice notation
Slice notation is defined by a start, stop and step values. When slicing by label, pandas includes the stop value in the return. The following slices from Aaron to Dean, inclusive. Its step size is not explicitly defined but defaulted to 1.
df.loc['Aaron':'Dean']
Complex slices can be taken in the same manner as Python lists.
.iloc selects data only by integer location
Let's now turn to .iloc. Every row and column of data in a DataFrame has an integer location that defines it. This is in addition to the label that is visually displayed in the output. The integer location is simply the number of rows/columns from the top/left beginning at 0.
There are many different inputs you can use for .iloc three out of them are
- An integer
- A list of integers
- Slice notation using integers as the start and stop values
Selecting a single row with .iloc with an integer
df.iloc[4]
This returns the 5th row (integer location 4) as a Series
age 32
color gray
food Cheese
height 180
score 1.8
state AK
Name: Dean, dtype: object
Selecting multiple rows with .iloc with a list of integers
df.iloc[[2, -2]]
This returns a DataFrame of the third and second to last rows:
Selecting multiple rows with .iloc with slice notation
df.iloc[:5:3]
Simultaneous selection of rows and columns with .loc and .iloc
One excellent ability of both .loc/.iloc is their ability to select both rows and columns simultaneously. In the examples above, all the columns were returned from each selection. We can choose columns with the same types of inputs as we do for rows. We simply need to separate the row and column selection with a comma.
For example, we can select rows Jane, and Dean with just the columns height, score and state like this:
df.loc[['Jane', 'Dean'], 'height':]
This uses a list of labels for the rows and slice notation for the columns
We can naturally do similar operations with .iloc using only integers.
df.iloc[[1,4], 2]
Nick Lamb
Dean Cheese
Name: food, dtype: object
Simultaneous selection with labels and integer location
.ix was used to make selections simultaneously with labels and integer location which was useful but confusing and ambiguous at times and thankfully it has been deprecated. In the event that you need to make a selection with a mix of labels and integer locations, you will have to make both your selections labels or integer locations.
For instance, if we want to select rows Nick and Cornelia along with columns 2 and 4, we could use .loc by converting the integers to labels with the following:
col_names = df.columns[[2, 4]]
df.loc[['Nick', 'Cornelia'], col_names]
Or alternatively, convert the index labels to integers with the get_loc index method.
labels = ['Nick', 'Cornelia']
index_ints = [df.index.get_loc(label) for label in labels]
df.iloc[index_ints, [2, 4]]
Boolean Selection
The .loc indexer can also do boolean selection. For instance, if we are interested in finding all the rows where age is above 30 and return just the food and score columns we can do the following:
df.loc[df['age'] > 30, ['food', 'score']]
You can replicate this with .iloc but you cannot pass it a boolean series. You must convert the boolean Series into a numpy array like this:
df.iloc[(df['age'] > 30).values, [2, 4]]
Selecting all rows
It is possible to use .loc/.iloc for just column selection. You can select all the rows by using a colon like this:
df.loc[:, 'color':'score':2]
The indexing operator, [], can slice can select rows and columns too but not simultaneously.
Most people are familiar with the primary purpose of the DataFrame indexing operator, which is to select columns. A string selects a single column as a Series and a list of strings selects multiple columns as a DataFrame.
df['food']
Jane Steak
Nick Lamb
Aaron Mango
Penelope Apple
Dean Cheese
Christina Melon
Cornelia Beans
Name: food, dtype: object
Using a list selects multiple columns
df[['food', 'score']]
What people are less familiar with, is that, when slice notation is used, then selection happens by row labels or by integer location. This is very confusing and something that I almost never use but it does work.
df['Penelope':'Christina'] # slice rows by label
df[2:6:2] # slice rows by integer location
The explicitness of .loc/.iloc for selecting rows is highly preferred. The indexing operator alone is unable to select rows and columns simultaneously.
df[3:5, 'color']
TypeError: unhashable type: 'slice'
Selection by .at and .iat
Selection with .at is nearly identical to .loc but it only selects a single 'cell' in your DataFrame. We usually refer to this cell as a scalar value. To use .at, pass it both a row and column label separated by a comma.
df.at['Christina', 'color']
'black'
Selection with .iat is nearly identical to .iloc but it only selects a single scalar value. You must pass it an integer for both the row and column locations
df.iat[2, 5]
'FL'
Array vs. Object efficiency in JavaScript
It's not really a performance question at all, since arrays and objects work very differently (or are supposed to, at least). Arrays have a continuous index 0..n, while objects map arbitrary keys to arbitrary values. If you want to supply specific keys, the only choice is an object. If you don't care about the keys, an array it is.
If you try to set arbitrary (numeric) keys on an array, you really have a performance loss, since behaviourally the array will fill in all indexes in-between:
> foo = [];
[]
> foo[100] = 'a';
"a"
> foo
[undefined, undefined, undefined, ..., "a"]
(Note that the array does not actually contain 99 undefined values, but it will behave this way since you're [supposed to be] iterating the array at some point.)
The literals for both options should make it very clear how they can be used:
var arr = ['foo', 'bar', 'baz']; // no keys, not even the option for it
var obj = { foo : 'bar', baz : 42 }; // associative by its very nature
How to change the playing speed of videos in HTML5?
You can use this code:
var vid = document.getElementById("video1");
function slowPlaySpeed() {
vid.playbackRate = 0.5;
}
function normalPlaySpeed() {
vid.playbackRate = 1;
}
function fastPlaySpeed() {
vid.playbackRate = 2;
}
Entity Framework is Too Slow. What are my options?
You should start by profiling the SQL commands actually issued by the Entity Framework. Depending on your configuration (POCO, Self-Tracking entities) there is a lot room for optimizations. You can debug the SQL commands (which shouldn't differ between debug and release mode) using the ObjectSet<T>.ToTraceString() method. If you encounter a query that requires further optimization you can use some projections to give EF more information about what you trying to accomplish.
Example:
Product product = db.Products.SingleOrDefault(p => p.Id == 10);
// executes SELECT * FROM Products WHERE Id = 10
ProductDto dto = new ProductDto();
foreach (Category category in product.Categories)
// executes SELECT * FROM Categories WHERE ProductId = 10
{
dto.Categories.Add(new CategoryDto { Name = category.Name });
}
Could be replaced with:
var query = from p in db.Products
where p.Id == 10
select new
{
p.Name,
Categories = from c in p.Categories select c.Name
};
ProductDto dto = new ProductDto();
foreach (var categoryName in query.Single().Categories)
// Executes SELECT p.Id, c.Name FROM Products as p, Categories as c WHERE p.Id = 10 AND p.Id = c.ProductId
{
dto.Categories.Add(new CategoryDto { Name = categoryName });
}
I just typed that out of my head, so this isn't exactly how it would be executed, but EF actually does some nice optimizations if you tell it everything you know about the query (in this case, that we will need the category-names). But this isn't like eager-loading (db.Products.Include("Categories")) because projections can further reduce the amount of data to load.
Is < faster than <=?
I see that neither is faster. The compiler generates the same machine code in each condition with a different value.
if(a < 901)
cmpl $900, -4(%rbp)
jg .L2
if(a <=901)
cmpl $901, -4(%rbp)
jg .L3
My example if is from GCC on x86_64 platform on Linux.
Compiler writers are pretty smart people, and they think of these things and many others most of us take for granted.
I noticed that if it is not a constant, then the same machine code is generated in either case.
int b;
if(a < b)
cmpl -4(%rbp), %eax
jge .L2
if(a <=b)
cmpl -4(%rbp), %eax
jg .L3
INNER JOIN vs LEFT JOIN performance in SQL Server
Outer joins can offer superior performance when used in views.
Say you have a query that involves a view, and that view is comprised of 10 tables joined together. Say your query only happens to use columns from 3 out of those 10 tables.
If those 10 tables had been inner-joined together, then the query optimizer would have to join them all even though your query itself doesn't need 7 out of 10 of the tables. That's because the inner joins themselves might filter down the data, making them essential to compute.
If those 10 tables had been outer-joined together instead, then the query optimizer would only actually join the ones that were necessary: 3 out of 10 of them in this case. That's because the joins themselves are no longer filtering the data, and thus unused joins can be skipped.
Source: http://www.sqlservercentral.com/blogs/sql_coach/2010/07/29/poor-little-misunderstood-views/
Using lambda expressions for event handlers
Performance-wise it's the same as a named method. The big problem is when you do the following:
MyButton.Click -= (o, i) =>
{
//snip
}
It will probably try to remove a different lambda, leaving the original one there. So the lesson is that it's fine unless you also want to be able to remove the handler.
Why do people say that Ruby is slow?
First of all, slower with respect to what? C? Python? Let's get some numbers at the Computer Language Benchmarks Game:
- Ruby 1.9 vs. Python3 within the same order of magnitude
- Ruby 1.9 vs. PHP within the same order of magnitude
- Ruby 1.9 vs. Java 6 server up to two orders of magnitude slower!
- Ruby 1.9 vs. C (gcc) up to two orders of magnitude slower!
- ...
Why is Ruby considered slow?
Depends on whom you ask. You could be told that:
- Ruby is an interpreted language and interpreted languages will tend to be slower than compiled ones
- Ruby uses garbage collection (though C#, which also uses garbage collection, comes out two orders of magnitude ahead of Ruby, Python, PHP etc. in the more algorithmic, less memory-allocation-intensive benchmarks above)
- Ruby method calls are slow (although, because of duck typing, they are arguably faster than in strongly typed interpreted languages)
- Ruby (with the exception of JRuby) does not support true multithreading
- etc.
But, then again, slow with respect to what? Ruby 1.9 is about as fast as Python and PHP (within a 3x performance factor) when compared to C (which can be up to 300x faster), so the above (with the exception of threading considerations, should your application heavily depend on this aspect) are largely academic.
What are your options as a Ruby programmer if you want to deal with this "slowness"?
Write for scalability and throw more hardware at it (e.g. memory)
Which version of Ruby would best suit an application like Stack Overflow where speed is critical and traffic is intense?
Well, REE (combined with Passenger) would be a very good candidate.
numpy: most efficient frequency counts for unique values in an array
import pandas as pd
import numpy as np
print(pd.Series(name_of_array).value_counts())
Fastest way to remove non-numeric characters from a VARCHAR in SQL Server
I'd use an Inline Function from performance perspective, see below: Note that symbols like '+','-' etc will not be removed
CREATE FUNCTION [dbo].[UDF_RemoveNumericStringsFromString]
(
@str varchar(100)
)
RETURNS TABLE AS RETURN
WITH Tally (n) as
(
-- 100 rows
SELECT TOP (Len(@Str)) ROW_NUMBER() OVER (ORDER BY (SELECT NULL))
FROM (VALUES (0),(0),(0),(0),(0),(0),(0),(0),(0),(0)) a(n)
CROSS JOIN (VALUES(0),(0),(0),(0),(0),(0),(0),(0),(0),(0)) b(n)
)
SELECT OutStr = STUFF(
(SELECT SUBSTRING(@Str, n,1) st
FROM Tally
WHERE ISNUMERIC(SUBSTRING(@Str, n,1)) = 1
FOR XML PATH(''),type).value('.', 'varchar(100)'),1,0,'')
GO
/*Use it*/
SELECT OutStr
FROM dbo.UDF_RemoveNumericStringsFromString('fjkfhk759734977fwe9794t23')
/*Result set
759734977979423 */
You can define it with more than 100 characters...
Performing a Stress Test on Web Application?
We have developed a process that treats load and performance measurenment as a first-class concern - as you say, leaving it to the end of the project tends to lead to disappointment...
So, during development, we include very basic multi-user testing (using selenium), which checks for basic craziness like broken session management, obvious concurrency issues, and obvious resource contention problems. Non-trivial projects include this in the continuous integration process, so we get very regular feedback.
For projects that don't have extreme performance requirements, we include basic performance testing in our testing; usually, we script out the tests using BadBoy, and import them into JMeter, replacing the login details and other thread-specific things. We then ramp these up to the level that the server is dealing with 100 requests per second; if the response time is less than 1 second, that's usually sufficient. We launch and move on with our lives.
For projects with extreme performance requirements, we still use BadBoy and JMeter, but put a lot of energy into understanding the bottlenecks on the servers on our test rig(web and database servers, usually). There's a good tool for analyzing Microsoft event logs which helps a lot with this. We typically find unexpected bottlenecks, which we optimize if possible; that gives us an application that is as fast as it can be on "1 web server, 1 database server". We then usually deploy to our target infrastructure, and use one of the "Jmeter in the cloud" services to re-run the tests at scale.
Again, PAL reports help to analyze what happened during the tests - you often see very different bottlenecks on production environments.
The key is to make sure you don't just run your stress tests, but also that you collect the information you need to understand the performance of your application.
What Process is using all of my disk IO
To find out which processes in state 'D' (waiting for disk response) are currently running:
while true; do date; ps aux | awk '{if($8=="D") print $0;}'; sleep 1; done
or
watch -n1 -d "ps axu | awk '{if (\$8==\"D\") {print \$0}}'"
Wed Aug 29 13:00:46 CLT 2012
root 321 0.0 0.0 0 0 ? D May28 4:25 \_ [jbd2/dm-0-8]
Wed Aug 29 13:00:47 CLT 2012
Wed Aug 29 13:00:48 CLT 2012
Wed Aug 29 13:00:49 CLT 2012
Wed Aug 29 13:00:50 CLT 2012
root 321 0.0 0.0 0 0 ? D May28 4:25 \_ [jbd2/dm-0-8]
Wed Aug 29 13:00:51 CLT 2012
Wed Aug 29 13:00:52 CLT 2012
Wed Aug 29 13:00:53 CLT 2012
Wed Aug 29 13:00:55 CLT 2012
Wed Aug 29 13:00:56 CLT 2012
root 321 0.0 0.0 0 0 ? D May28 4:25 \_ [jbd2/dm-0-8]
Wed Aug 29 13:00:57 CLT 2012
root 302 0.0 0.0 0 0 ? D May28 3:07 \_ [kdmflush]
root 321 0.0 0.0 0 0 ? D May28 4:25 \_ [jbd2/dm-0-8]
Wed Aug 29 13:00:58 CLT 2012
root 302 0.0 0.0 0 0 ? D May28 3:07 \_ [kdmflush]
root 321 0.0 0.0 0 0 ? D May28 4:25 \_ [jbd2/dm-0-8]
Wed Aug 29 13:00:59 CLT 2012
root 302 0.0 0.0 0 0 ? D May28 3:07 \_ [kdmflush]
root 321 0.0 0.0 0 0 ? D May28 4:25 \_ [jbd2/dm-0-8]
Wed Aug 29 13:01:00 CLT 2012
root 302 0.0 0.0 0 0 ? D May28 3:07 \_ [kdmflush]
root 321 0.0 0.0 0 0 ? D May28 4:25 \_ [jbd2/dm-0-8]
Wed Aug 29 13:01:01 CLT 2012
root 302 0.0 0.0 0 0 ? D May28 3:07 \_ [kdmflush]
root 321 0.0 0.0 0 0 ? D May28 4:25 \_ [jbd2/dm-0-8]
Wed Aug 29 13:01:02 CLT 2012
Wed Aug 29 13:01:03 CLT 2012
root 321 0.0 0.0 0 0 ? D May28 4:25 \_ [jbd2/dm-0-8]
As you can see from the result, the jdb2/dm-0-8 (ext4 journal process), and kdmflush are constantly block your Linux.
For more details this URL could be helpful: Linux Wait-IO Problem
What is the most efficient way to loop through dataframes with pandas?
Like what has been mentioned before, pandas object is most efficient when process the whole array at once. However for those who really need to loop through a pandas DataFrame to perform something, like me, I found at least three ways to do it. I have done a short test to see which one of the three is the least time consuming.
t = pd.DataFrame({'a': range(0, 10000), 'b': range(10000, 20000)})
B = []
C = []
A = time.time()
for i,r in t.iterrows():
C.append((r['a'], r['b']))
B.append(time.time()-A)
C = []
A = time.time()
for ir in t.itertuples():
C.append((ir[1], ir[2]))
B.append(time.time()-A)
C = []
A = time.time()
for r in zip(t['a'], t['b']):
C.append((r[0], r[1]))
B.append(time.time()-A)
print B
Result:
[0.5639059543609619, 0.017839908599853516, 0.005645036697387695]
This is probably not the best way to measure the time consumption but it's quick for me.
Here are some pros and cons IMHO:
- .iterrows(): return index and row items in separate variables, but significantly slower
- .itertuples(): faster than .iterrows(), but return index together with row items, ir[0] is the index
- zip: quickest, but no access to index of the row
EDIT 2020/11/10
For what it is worth, here is an updated benchmark with some other alternatives (perf with MacBookPro 2,4 GHz Intel Core i9 8 cores 32 Go 2667 MHz DDR4)
import sys
import tqdm
import time
import pandas as pd
B = []
t = pd.DataFrame({'a': range(0, 10000), 'b': range(10000, 20000)})
for _ in tqdm.tqdm(range(10)):
C = []
A = time.time()
for i,r in t.iterrows():
C.append((r['a'], r['b']))
B.append({"method": "iterrows", "time": time.time()-A})
C = []
A = time.time()
for ir in t.itertuples():
C.append((ir[1], ir[2]))
B.append({"method": "itertuples", "time": time.time()-A})
C = []
A = time.time()
for r in zip(t['a'], t['b']):
C.append((r[0], r[1]))
B.append({"method": "zip", "time": time.time()-A})
C = []
A = time.time()
for r in zip(*t.to_dict("list").values()):
C.append((r[0], r[1]))
B.append({"method": "zip + to_dict('list')", "time": time.time()-A})
C = []
A = time.time()
for r in t.to_dict("records"):
C.append((r["a"], r["b"]))
B.append({"method": "to_dict('records')", "time": time.time()-A})
A = time.time()
t.agg(tuple, axis=1).tolist()
B.append({"method": "agg", "time": time.time()-A})
A = time.time()
t.apply(tuple, axis=1).tolist()
B.append({"method": "apply", "time": time.time()-A})
print(f'Python {sys.version} on {sys.platform}')
print(f"Pandas version {pd.__version__}")
print(
pd.DataFrame(B).groupby("method").agg(["mean", "std"]).xs("time", axis=1).sort_values("mean")
)
## Output
Python 3.7.9 (default, Oct 13 2020, 10:58:24)
[Clang 12.0.0 (clang-1200.0.32.2)] on darwin
Pandas version 1.1.4
mean std
method
zip + to_dict('list') 0.002353 0.000168
zip 0.003381 0.000250
itertuples 0.007659 0.000728
to_dict('records') 0.025838 0.001458
agg 0.066391 0.007044
apply 0.067753 0.006997
iterrows 0.647215 0.019600
How do I measure separate CPU core usage for a process?
The ps solution was nearly what I needed and with some bash thrown in does exactly what the original question asked for: to see per-core usage of specific processes
This shows per-core usage of multi-threaded processes too.
Use like: cpustat `pgrep processname` `pgrep otherprocessname` ...
#!/bin/bash
pids=()
while [ $# != 0 ]; do
pids=("${pids[@]}" "$1")
shift
done
if [ -z "${pids[0]}" ]; then
echo "Usage: $0 <pid1> [pid2] ..."
exit 1
fi
for pid in "${pids[@]}"; do
if [ ! -e /proc/$pid ]; then
echo "Error: pid $pid doesn't exist"
exit 1
fi
done
while [ true ]; do
echo -e "\033[H\033[J"
for pid in "${pids[@]}"; do
ps -p $pid -L -o pid,tid,psr,pcpu,comm=
done
sleep 1
done
Note: These stats are based on process lifetime, not the last X seconds, so you'll need to restart your process to reset the counter.
Declaring multiple variables in JavaScript
It's just a matter of personal preference. There is no difference between these two ways, other than a few bytes saved with the second form if you strip out the white space.
SQL, Postgres OIDs, What are they and why are they useful?
If you still use OID, it would be better to remove the dependency on it, because in recent versions of Postgres it is no longer supported. This can stop (temporarily until you solve it) your migration from version 10 to 12 for example.
See also: https://dev.to/rafaelbernard/postgresql-pgupgrade-from-10-to-12-566i
for or while loop to do something n times
The fundamental difference in most programming languages is that unless the unexpected happens a for loop will always repeat n times or until a break statement, (which may be conditional), is met then finish with a while loop it may repeat 0 times, 1, more or even forever, depending on a given condition which must be true at the start of each loop for it to execute and always false on exiting the loop, (for completeness a do ... while loop, (or repeat until), for languages that have it, always executes at least once and does not guarantee the condition on the first execution).
It is worth noting that in Python a for or while statement can have break, continue and else statements where:
break- terminates the loopcontinue- moves on to the next time around the loop without executing following code this time aroundelse- is executed if the loop completed without anybreakstatements being executed.
N.B. In the now unsupported Python 2 range produced a list of integers but you could use xrange to use an iterator. In Python 3 range returns an iterator.
So the answer to your question is 'it all depends on what you are trying to do'!
How can I read a large text file line by line using Java?
BufferedReader br;
FileInputStream fin;
try {
fin = new FileInputStream(fileName);
br = new BufferedReader(new InputStreamReader(fin));
/*Path pathToFile = Paths.get(fileName);
br = Files.newBufferedReader(pathToFile,StandardCharsets.US_ASCII);*/
String line = br.readLine();
while (line != null) {
String[] attributes = line.split(",");
Movie movie = createMovie(attributes);
movies.add(movie);
line = br.readLine();
}
fin.close();
br.close();
} catch (FileNotFoundException e) {
System.out.println("Your Message");
} catch (IOException e) {
System.out.println("Your Message");
}
It works for me. Hope It will help you too.
What is the relative performance difference of if/else versus switch statement in Java?
Use switch!
I hate to maintain if-else-blocks! Have a test:
public class SpeedTestSwitch
{
private static void do1(int loop)
{
int temp = 0;
for (; loop > 0; --loop)
{
int r = (int) (Math.random() * 10);
switch (r)
{
case 0:
temp = 9;
break;
case 1:
temp = 8;
break;
case 2:
temp = 7;
break;
case 3:
temp = 6;
break;
case 4:
temp = 5;
break;
case 5:
temp = 4;
break;
case 6:
temp = 3;
break;
case 7:
temp = 2;
break;
case 8:
temp = 1;
break;
case 9:
temp = 0;
break;
}
}
System.out.println("ignore: " + temp);
}
private static void do2(int loop)
{
int temp = 0;
for (; loop > 0; --loop)
{
int r = (int) (Math.random() * 10);
if (r == 0)
temp = 9;
else
if (r == 1)
temp = 8;
else
if (r == 2)
temp = 7;
else
if (r == 3)
temp = 6;
else
if (r == 4)
temp = 5;
else
if (r == 5)
temp = 4;
else
if (r == 6)
temp = 3;
else
if (r == 7)
temp = 2;
else
if (r == 8)
temp = 1;
else
if (r == 9)
temp = 0;
}
System.out.println("ignore: " + temp);
}
public static void main(String[] args)
{
long time;
int loop = 1 * 100 * 1000 * 1000;
System.out.println("warming up...");
do1(loop / 100);
do2(loop / 100);
System.out.println("start");
// run 1
System.out.println("switch:");
time = System.currentTimeMillis();
do1(loop);
System.out.println(" -> time needed: " + (System.currentTimeMillis() - time));
// run 2
System.out.println("if/else:");
time = System.currentTimeMillis();
do2(loop);
System.out.println(" -> time needed: " + (System.currentTimeMillis() - time));
}
}
Java check if boolean is null
boolean is a primitive type, and therefore can not be null.
Its boxed type, Boolean, can be null.
The function is probably returning a Boolean as opposed to a boolean, so assigning the result to a Boolean-type variable will allow you to test for nullity.
how to check if a datareader is null or empty
In addition to the suggestions given, you can do this directly from your query like this -
SELECT ISNULL([Additional], -1) AS [Additional]
This way you can write the condition to check whether the field value is < 0 or >= 0.
How do I use Ruby for shell scripting?
In ruby, the constant __FILE__ will always give you the path of the script you're running.
On Linux, /usr/bin/env is your friend:
#! /usr/bin/env ruby
# Extension of this script does not matter as long
# as it is executable (chmod +x)
puts File.expand_path(__FILE__)
On Windows it depends whether or not .rb files are associated with ruby. If they are:
# This script filename must end with .rb
puts File.expand_path(__FILE__)
If they are not, you have to explicitly invoke ruby on them, I use a intermediate .cmd file:
my_script.cmd:
@ruby %~dp0\my_script.rb
my_script.rb:
puts File.expand_path(__FILE__)
MongoDB - admin user not authorized
For MongoDB shell version v4.2.8 I've tried different ways to back-up my database with auth, my winner solution is
mongodump -h <your_hostname> -d <your_db_name> -u <your_db_username> -p <your_db_password> --authenticationDatabase admin -o /path/to/where/i/want
Explain the "setUp" and "tearDown" Python methods used in test cases
Suppose you have a suite with 10 tests. 8 of the tests share the same setup/teardown code. The other 2 don't.
setup and teardown give you a nice way to refactor those 8 tests. Now what do you do with the other 2 tests? You'd move them to another testcase/suite. So using setup and teardown also helps give a natural way to break the tests into cases/suites
Difference between a User and a Login in SQL Server
One reason to have both is so that authentication can be done by the database server, but authorization can be scoped to the database. That way, if you move your database to another server, you can always remap the user-login relationship on the database server, but your database doesn't have to change.
A weighted version of random.choice
import numpy as np
w=np.array([ 0.4, 0.8, 1.6, 0.8, 0.4])
np.random.choice(w, p=w/sum(w))
Difference between "module.exports" and "exports" in the CommonJs Module System
Also, one things that may help to understand:
math.js
this.add = function (a, b) {
return a + b;
};
client.js
var math = require('./math');
console.log(math.add(2,2); // 4;
Great, in this case:
console.log(this === module.exports); // true
console.log(this === exports); // true
console.log(module.exports === exports); // true
Thus, by default, "this" is actually equals to module.exports.
However, if you change your implementation to:
math.js
var add = function (a, b) {
return a + b;
};
module.exports = {
add: add
};
In this case, it will work fine, however, "this" is not equal to module.exports anymore, because a new object was created.
console.log(this === module.exports); // false
console.log(this === exports); // true
console.log(module.exports === exports); // false
And now, what will be returned by the require is what was defined inside the module.exports, not this or exports, anymore.
Another way to do it would be:
math.js
module.exports.add = function (a, b) {
return a + b;
};
Or:
math.js
exports.add = function (a, b) {
return a + b;
};
.gitignore is ignored by Git
Even if you haven't tracked the files so far, Git seems to be able to "know" about them even after you add them to .gitignore.
WARNING: First commit or stash your current changes, or you will lose them.
Then run the following commands from the top folder of your Git repository:
git rm -r --cached .
git add .
git commit -m "fixed untracked files"
Is there a way to crack the password on an Excel VBA Project?
The accepted answer didn't work in Excel 2019 on Windows 10. Found out the extra steps we need to take to see the locked macro. I am summarizing the steps.
Add a .zip to the end of the excel filename and hit enter
Once the file has been changed to a ZIP file, open it by double clicking on it
Inside you would see a folder called xl like below
Inside xl, you'll find a file called vbaProject.bin, copy/paste it on the desktop
Go to the online Hexadecimal Editor HexEd.it
Search for the following texts DPB=... and change them to DPx=...
Save the file and close HexEd.it
Copy/Paste the updated file from your desktop inside the ZIP file (you would need to overwrite it)
Remove the .zip extension from the end of the filename and add the excel extention again.
Open the file in excel - you may receive a couple of error notifications, just click through them.
==== EXTRA STEPS OVER THE ACCEPTED ANSWER =====
- Open the Visual Basic window (usually ALT+F11 if I remember correctly) and open the VBAProject properties (Tools menu).
- Click on the Protection tab and change (do not remove at this stage) the password to something short and easy to remember (we'll be removing in next step).
- Save the workbook and then close and reopen.
- Open again the Visual Basic window and enter the password you just put in. Redo the previous step but this time you can remove (delete) the password.
- Save the workbook and you have now removed the password.
Extra steps are taken from following site https://confluence.jaytaala.com/display/TKB/Remove+Excel+VBA+password
Setting default value for TypeScript object passed as argument
No, TypeScript doesn't have a natural way of setting defaults for properties of an object defined like that where one has a default and the other does not. You could define a richer structure:
class Name {
constructor(public first : string,
public last: string = "Smith") {
}
}
And use that in place of the inline type definition.
function sayName(name: Name) {
alert(name.first + " " + name.last);
}
You can't do something like this unfortunately:
function sayName(name : { first: string; last?:string }
/* and then assign a default object matching the signature */
= { first: null, last: 'Smith' }) {
}
As it would only set the default if name was undefined.
How to get ID of button user just clicked?
$("button").click(function() {
alert(this.id); // or alert($(this).attr('id'));
});
How do I pass a list as a parameter in a stored procedure?
You can use this simple 'inline' method to construct a string_list_type parameter (works in SQL Server 2014):
declare @p1 dbo.string_list_type
insert into @p1 values(N'myFirstString')
insert into @p1 values(N'mySecondString')
Example use when executing a stored proc:
exec MyStoredProc @MyParam=@p1
Description Box using "onmouseover"
Assuming popup is the ID of your "description box":
HTML
<div id="parent"> <!-- This is the main container, to mouse over -->
<div id="popup" style="display: none">description text here</div>
</div>
JavaScript
var e = document.getElementById('parent');
e.onmouseover = function() {
document.getElementById('popup').style.display = 'block';
}
e.onmouseout = function() {
document.getElementById('popup').style.display = 'none';
}
Alternatively you can get rid of JavaScript entirely and do it just with CSS:
CSS
#parent #popup {
display: none;
}
#parent:hover #popup {
display: block;
}
Add a reference column migration in Rails 4
Another syntax of doing the same thing is:
rails g migration AddUserToUpload user:belongs_to
How do I implement interfaces in python?
My understanding is that interfaces are not that necessary in dynamic languages like Python. In Java (or C++ with its abstract base class) interfaces are means for ensuring that e.g. you're passing the right parameter, able to perform set of tasks.
E.g. if you have observer and observable, observable is interested in subscribing objects that supports IObserver interface, which in turn has notify action. This is checked at compile time.
In Python, there is no such thing as compile time and method lookups are performed at runtime. Moreover, one can override lookup with __getattr__() or __getattribute__() magic methods. In other words, you can pass, as observer, any object that can return callable on accessing notify attribute.
This leads me to the conclusion, that interfaces in Python do exist - it's just their enforcement is postponed to the moment in which they are actually used
Disable Transaction Log
SQL Server requires a transaction log in order to function.
That said there are two modes of operation for the transaction log:
- Simple
- Full
In Full mode the transaction log keeps growing until you back up the database. In Simple mode: space in the transaction log is 'recycled' every Checkpoint.
Very few people have a need to run their databases in the Full recovery model. The only point in using the Full model is if you want to backup the database multiple times per day, and backing up the whole database takes too long - so you just backup the transaction log.
The transaction log keeps growing all day, and you keep backing just it up. That night you do your full backup, and SQL Server then truncates the transaction log, begins to reuse the space allocated in the transaction log file.
If you only ever do full database backups, you don't want the Full recovery mode.
Generating a Random Number between 1 and 10 Java
As the documentation says, this method call returns "a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive)". This means that you will get numbers from 0 to 9 in your case. So you've done everything correctly by adding one to that number.
Generally speaking, if you need to generate numbers from min to max (including both), you write
random.nextInt(max - min + 1) + min
How to load GIF image in Swift?
You can try this new library. JellyGif respects Gif frame duration while being highly CPU & Memory performant. It works great with UITableViewCell & UICollectionViewCell too. To get started you just need to
import JellyGif
let imageView = JellyGifImageView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
//Animates Gif from the main bundle
imageView.startGif(with: .name("Gif name"))
//Animates Gif with a local path
let url = URL(string: "Gif path")!
imageView.startGif(with: .localPath(url))
//Animates Gif with data
imageView.startGif(with: .data(Data))
For more information you can look at its README
jQuery AJAX file upload PHP
var formData = new FormData($("#YOUR_FORM_ID")[0]);
$.ajax({
url: "upload.php",
type: "POST",
data : formData,
processData: false,
contentType: false,
beforeSend: function() {
},
success: function(data){
},
error: function(xhr, ajaxOptions, thrownError) {
console.log(thrownError + "\r\n" + xhr.statusText + "\r\n" + xhr.responseText);
}
});
lists and arrays in VBA
You will have to change some of your data types but the basics of what you just posted could be converted to something similar to this given the data types I used may not be accurate.
Dim DateToday As String: DateToday = Format(Date, "yyyy/MM/dd")
Dim Computers As New Collection
Dim disabledList As New Collection
Dim compArray(1 To 1) As String
'Assign data to first item in array
compArray(1) = "asdf"
'Format = Item, Key
Computers.Add "ErrorState", "Computer Name"
'Prints "ErrorState"
Debug.Print Computers("Computer Name")
Collections cannot be sorted so if you need to sort data you will probably want to use an array.
Here is a link to the outlook developer reference. http://msdn.microsoft.com/en-us/library/office/ff866465%28v=office.14%29.aspx
Another great site to help you get started is http://www.cpearson.com/Excel/Topic.aspx
Moving everything over to VBA from VB.Net is not going to be simple since not all the data types are the same and you do not have the .Net framework. If you get stuck just post the code you're stuck converting and you will surely get some help!
Edit:
Sub ArrayExample()
Dim subject As String
Dim TestArray() As String
Dim counter As Long
subject = "Example"
counter = Len(subject)
ReDim TestArray(1 To counter) As String
For counter = 1 To Len(subject)
TestArray(counter) = Right(Left(subject, counter), 1)
Next
End Sub
EF Code First "Invalid column name 'Discriminator'" but no inheritance
this error happen with me because I did the following
- I changed Column name of table in database
- (I did not used
Update Model from databasein Edmx) I Renamed manually Property name to match the change in database schema - I did some refactoring to change name of the property in the class to be the same as database schema and models in Edmx
Although all of this, I got this error
so what to do
- I Deleted the model from Edmx
- Right Click and
Update Model from database
this will regenerate the model, and entity framework will not give you this error
hope this help you
Oracle to_date, from mm/dd/yyyy to dd-mm-yyyy
select to_char(to_date('1/21/2000','mm/dd/yyyy'),'dd-mm-yyyy') from dual
How do I declare a namespace in JavaScript?
In JavaScript there are no predefined methods to use namespaces. In JavaScript we have to create our own methods to define NameSpaces. Here is a procedure we follow in Oodles technologies.
Register a NameSpace Following is the function to register a name space
//Register NameSpaces Function
function registerNS(args){
var nameSpaceParts = args.split(".");
var root = window;
for(var i=0; i < nameSpaceParts.length; i++)
{
if(typeof root[nameSpaceParts[i]] == "undefined")
root[nameSpaceParts[i]] = new Object();
root = root[nameSpaceParts[i]];
}
}
To register a Namespace just call the above function with the argument as name space separated by '.' (dot).
For Example
Let your application name is oodles. You can make a namespace by following method
registerNS("oodles.HomeUtilities");
registerNS("oodles.GlobalUtilities");
var $OHU = oodles.HomeUtilities;
var $OGU = oodles.GlobalUtilities;
Basically it will create your NameSpaces structure like below in backend:
var oodles = {
"HomeUtilities": {},
"GlobalUtilities": {}
};
In the above function you have register a namespace called "oodles.HomeUtilities" and "oodles.GlobalUtilities". To call these namespaces we make an variable i.e. var $OHU and var $OGU.
These variables are nothing but an alias to Intializing the namespace.
Now, Whenever you declare a function that belong to HomeUtilities you will declare it like following:
$OHU.initialization = function(){
//Your Code Here
};
Above is the function name initialization and it is put into an namespace $OHU. and to call this function anywhere in the script files. Just use following code.
$OHU.initialization();
Similarly, with the another NameSpaces.
Hope it helps.
How to align LinearLayout at the center of its parent?
This worked for me.. adding empty view ..
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:orientation="horizontal"
>
<View
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_weight="1"
/>
<com.google.android.gms.ads.AdView
android:id="@+id/adView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
ads:adSize="BANNER"
ads:adUnitId="@string/banner_ad_unit_id" >
</com.google.android.gms.ads.AdView>
<View
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_weight="1"
/>
</LinearLayout>
LEFT INNER JOIN vs. LEFT OUTER JOIN - Why does the OUTER take longer?
Wait -- did you actually mean that "the same number of rows ... are being processed" or that "the same number of rows are being returned"? In general, the outer join would process many more rows, including those for which there is no match, even if it returns the same number of records.
Insert string in beginning of another string
Other answers explain how to insert a string at the beginning of another String or StringBuilder (or StringBuffer).
However, strictly speaking, you cannot insert a string into the beginning of another one. Strings in Java are immutable1.
When you write:
String s = "Jam";
s = "Hello " + s;
you are actually causing a new String object to be created that is the concatenation of "Hello " and "Jam". You are not actually inserting characters into an existing String object at all.
1 - It is technically possible to use reflection to break abstraction on String objects and mutate them ... even though they are immutable by design. But it is a really bad idea to do this. Unless you know that a String object was created explicitly via new String(...) it could be shared, or it could share internal state with other String objects. Finally, the JVM spec clearly states that the behavior of code that uses reflection to change a final is undefined. Mutation of String objects is dangerous.
How to add a constant column in a Spark DataFrame?
In spark 2.2 there are two ways to add constant value in a column in DataFrame:
1) Using lit
2) Using typedLit.
The difference between the two is that typedLit can also handle parameterized scala types e.g. List, Seq, and Map
Sample DataFrame:
val df = spark.createDataFrame(Seq((0,"a"),(1,"b"),(2,"c"))).toDF("id", "col1")
+---+----+
| id|col1|
+---+----+
| 0| a|
| 1| b|
+---+----+
1) Using lit: Adding constant string value in new column named newcol:
import org.apache.spark.sql.functions.lit
val newdf = df.withColumn("newcol",lit("myval"))
Result:
+---+----+------+
| id|col1|newcol|
+---+----+------+
| 0| a| myval|
| 1| b| myval|
+---+----+------+
2) Using typedLit:
import org.apache.spark.sql.functions.typedLit
df.withColumn("newcol", typedLit(("sample", 10, .044)))
Result:
+---+----+-----------------+
| id|col1| newcol|
+---+----+-----------------+
| 0| a|[sample,10,0.044]|
| 1| b|[sample,10,0.044]|
| 2| c|[sample,10,0.044]|
+---+----+-----------------+
Two arrays in foreach loop
foreach( $codes as $code and $names as $name ) { }
That is not valid.
You probably want something like this...
foreach( $codes as $index => $code ) {
echo '<option value="' . $code . '">' . $names[$index] . '</option>';
}
Alternatively, it'd be much easier to make the codes the key of your $names array...
$names = array(
'tn' => 'Tunisia',
'us' => 'United States',
...
);
How to solve error message: "Failed to map the path '/'."
You don't have to reset IIS, you can just recycle the app pool.
How to commit my current changes to a different branch in Git
You can just create a new branch and switch onto it. Commit your changes then:
git branch dirty
git checkout dirty
// And your commit follows ...
Alternatively, you can also checkout an existing branch (just git checkout <name>). But only, if there are no collisions (the base of all edited files is the same as in your current branch). Otherwise you will get a message.
Bootstrap 3 scrollable div for table
A scrolling comes from a box with class pre-scrollable
<div class="pre-scrollable"></div>
There's more examples: http://getbootstrap.com/css/#code-block
Wish it helps.
how to output every line in a file python
You could try this. It doesn't read all of f into memory at once (using the file object's iterator) and it closes the file when the code leaves the with block.
if data.find('!masters') != -1:
with open('masters.txt', 'r') as f:
for line in f:
print line
sck.send('PRIVMSG ' + chan + " " + line + '\r\n')
If you're using an older version of python (pre 2.6) you'll have to have
from __future__ import with_statement
Add shadow to custom shape on Android
The following worked for me: Just save as custom_shape.xml.
<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >
<!-- "shadow" -->
<item>
<shape android:shape="rectangle" >
<solid android:color="#000000"/>
<corners android:radius="12dp" />
</shape>
</item>
<item android:bottom="3px">
<shape android:shape="rectangle">
<solid android:color="#90ffffff"/>
<corners android:radius="12dp" />
</shape>
</item>
</layer-list>
Read line with Scanner
next() and nextLine() methods are associated with Scanner and is used for getting String inputs. Their differences are...
next() can read the input only till the space. It can't read two words separated by space. Also, next() places the cursor in the same line after reading the input.
nextLine() reads input including space between the words (that is, it reads till the end of line \n). Once the input is read, nextLine() positions the cursor in the next line.
Read article :Difference between next() and nextLine()
Replace your while loop with :
while(r.hasNext()) {
scan = r.next();
System.out.println(scan);
if(scan.length()==0) {continue;}
//treatment
}
Using hasNext() and next() methods will resolve the issue.
How should I declare default values for instance variables in Python?
Using class members for default values of instance variables is not a good idea, and it's the first time I've seen this idea mentioned at all. It works in your example, but it may fail in a lot of cases. E.g., if the value is mutable, mutating it on an unmodified instance will alter the default:
>>> class c:
... l = []
...
>>> x = c()
>>> y = c()
>>> x.l
[]
>>> y.l
[]
>>> x.l.append(10)
>>> y.l
[10]
>>> c.l
[10]
jQuery, simple polling example
This solution:
- has timeout
- polling works also after error response
Minimum version of jQuery is 1.12
$(document).ready(function () {
function poll () {
$.get({
url: '/api/stream/',
success: function (data) {
console.log(data)
},
timeout: 10000 // == 10 seconds timeout
}).always(function () {
setTimeout(poll, 30000) // == 30 seconds polling period
})
}
// start polling
poll()
})
Replacing characters in Ant property
Here is the solution without scripting and no external jars like ant-conrib:
The trick is to use ANT's resources:
- There is one resource type called "propertyresource" which is like a source file, but provides an stream from the string value of this resource. So you can load it and use it in any task like "copy" that accepts files
- There is also the task "loadresource" that can load any resource to a property (e.g., a file), but this one could also load our propertyresource. This task allows for filtering the input by applying some token transformations. Finally the following will do what you want:
<loadresource property="propB">
<propertyresource name="propA"/>
<filterchain>
<tokenfilter>
<filetokenizer/>
<replacestring from=" " to="_"/>
</tokenfilter>
</filterchain>
</loadresource>
This one will replace all " " in propA by "_" and place the result in propB. "filetokenizer" treats the whole input stream (our property) as one token and appies the string replacement on it.
You can do other fancy transformations using other tokenfilters: http://ant.apache.org/manual/Types/filterchain.html
SQL ORDER BY multiple columns
The results are ordered by the first column, then the second, and so on for as many columns as the ORDER BY clause includes. If you want any results sorted in descending order, your ORDER BY clause must use the DESC keyword directly after the name or the number of the relevant column.
Check out this Example
SELECT first_name, last_name, hire_date, salary
FROM employee
ORDER BY hire_date DESC,last_name ASC;
It will order in succession. Order the Hire_Date first, then LAST_NAME it by Hire_Date .
How do I change the font color in an html table?
if you need to change specific option from the select menu you can do it like this
option[value="Basic"] {
color:red;
}
or you can change them all
select {
color:red;
}
shuffling/permutating a DataFrame in pandas
Sampling randomizes, so just sample the entire data frame.
df.sample(frac=1)
Why should a Java class implement comparable?
When you implement Comparable interface, you need to implement method compareTo(). You need it to compare objects, in order to use, for example, sorting method of ArrayList class. You need a way to compare your objects to be able to sort them. So you need a custom compareTo() method in your class so you can use it with the ArrayList sort method. The compareTo() method returns -1,0,1.
I have just read an according chapter in Java Head 2.0, I'm still learning.
Export Postgresql table data using pgAdmin
- Right-click on your table and pick option
Backup.. - On File Options, set Filepath/Filename and pick
PLAINfor Format - Ignore Dump Options #1 tab
- In Dump Options #2 tab, check
USE INSERT COMMANDS - In Dump Options #2 tab, check
Use Column Insertsif you want column names in your inserts. - Hit
Backupbutton
HTML how to clear input using javascript?
You could use a placeholder because it does it for you, but for old browsers that don't support placeholder, try this:
<script>
function clearThis(target) {
if (target.value == "[email protected]") {
target.value = "";
}
}
function replace(target) {
if (target.value == "" || target.value == null) {
target.value == "[email protected]";
}
}
</script>
<input type="text" name="email" value="[email protected]" size="x" onfocus="clearThis(this)" onblur="replace(this)" />
CODE EXPLAINED: When the text box has focus, clear the value. When text box is not focused AND when the box is blank, replace the value.
I hope that works, I have been having the same issue, but then I tried this and it worked for me.
How to suppress "unused parameter" warnings in C?
In MSVC to suppress a particular warning it is enough to specify the it's number to compiler as /wd#. My CMakeLists.txt contains such the block:
If (MSVC)
Set (CMAKE_EXE_LINKER_FLAGS "$ {CMAKE_EXE_LINKER_FLAGS} / NODEFAULTLIB: LIBCMT")
Add_definitions (/W4 /wd4512 /wd4702 /wd4100 /wd4510 /wd4355 /wd4127)
Add_definitions (/D_CRT_SECURE_NO_WARNINGS)
Elseif (CMAKE_COMPILER_IS_GNUCXX OR CMAKE_COMPILER_IS_GNUC)
Add_definitions (-Wall -W -pedantic)
Else ()
Message ("Unknown compiler")
Endif ()
Now I can not say what exactly /wd4512 /wd4702 /wd4100 /wd4510 /wd4355 /wd4127 mean, because I do not pay any attention to MSVC for three years, but they suppress superpedantic warnings that does not influence the result.
Iterate over a Javascript associative array in sorted order
var a = new Array();_x000D_
a['b'] = 1;_x000D_
a['z'] = 1;_x000D_
a['a'] = 1;_x000D_
_x000D_
_x000D_
var keys=Object.keys(a).sort();_x000D_
for(var i=0,key=keys[0];i<keys.length;key=keys[++i]){_x000D_
document.write(key+' : '+a[key]+'<br>');_x000D_
}ValueError: unsupported format character while forming strings
You might have a typo.. In my case I was saying %w where I meant to say %s.
"Connection for controluser as defined in your configuration failed" with phpMyAdmin in XAMPP
Just comment out the whole "User for advanced features" and "Advanced phpMyAdmin features" code blocks in config.inc.php.
Get drop down value
var dd = document.getElementById("dropdownID");
var selectedItem = dd.options[dd.selectedIndex].value;
SQL Server ON DELETE Trigger
CREATE TRIGGER sampleTrigger
ON database1.dbo.table1
FOR DELETE
AS
DELETE FROM database2.dbo.table2
WHERE bar = 4 AND ID IN(SELECT deleted.id FROM deleted)
GO
Syntax for an If statement using a boolean
You can change the value of a bool all you want. As for an if:
if randombool == True:
works, but you can also use:
if randombool:
If you want to test whether something is false you can use:
if randombool == False
but you can also use:
if not randombool:
Defining constant string in Java?
We usually declare the constant as static. The reason for that is because Java creates copies of non static variables every time you instantiate an object of the class.
So if we make the constants static it would not do so and would save memory.
With final we can make the variable constant.
Hence the best practice to define a constant variable is the following:
private static final String YOUR_CONSTANT = "Some Value";
The access modifier can be private/public depending on the business logic.
what is .subscribe in angular?
In Angular (currently on Angular-6) .subscribe() is a method on the Observable type. The Observable type is a utility that asynchronously or synchronously streams data to a variety of components or services that have subscribed to the observable.
The observable is an implementation/abstraction over the promise chain and will be a part of ES7 as a proposed and very supported feature. In Angular it is used internally due to rxjs being a development dependency.
An observable itself can be thought of as a stream of data coming from a source, in Angular this source is an API-endpoint, a service, a database or another observable. But the power it has is that it's not expecting a single response. It can have one or many values that are returned.
Link to rxjs for observable/subscribe docs here: https://rxjs-dev.firebaseapp.com/api/index/class/Observable#subscribe-
Subscribe takes 3 methods as parameters each are functions:
- next: For each item being emitted by the observable perform this function
- error: If somewhere in the stream an error is found, do this method
- complete: Once all items are complete from the stream, do this method
Within each of these, there is the potentional to pipe (or chain) other utilities called operators onto the results to change the form or perform some layered logic.
In the simple example above:
.subscribe(hero => this.hero = hero); basically says on this observable take the hero being emitted and set it to this.hero.
Adding this answer to give more context to Observables based off the documentation and my understanding.
pinpointing "conditional jump or move depends on uninitialized value(s)" valgrind message
What this means is that you are trying to print out/output a value which is at least partially uninitialized. Can you narrow it down so that you know exactly what value that is? After that, trace through your code to see where it is being initialized. Chances are, you will see that it is not being fully initialized.
If you need more help, posting the relevant sections of source code might allow someone to offer more guidance.
EDIT
I see you've found the problem. Note that valgrind watches for Conditional jump or move based on unitialized variables. What that means is that it will only give out a warning if the execution of the program is altered due to the uninitialized value (ie. the program takes a different branch in an if statement, for example). Since the actual arithmetic did not involve a conditional jump or move, valgrind did not warn you of that. Instead, it propagated the "uninitialized" status to the result of the statement that used it.
It may seem counterintuitive that it does not warn you immediately, but as mark4o pointed out, it does this because uninitialized values get used in C all the time (examples: padding in structures, the realloc() call, etc.) so those warnings would not be very useful due to the false positive frequency.
php implode (101) with quotes
Another possible option, depending on what you need the array for:
$array = array('lastname', 'email', 'phone');
echo json_encode($array);
This will put '[' and ']' around the string, which you may or may not want.
Getter and Setter of Model object in Angular 4
The way you declare the date property as an input looks incorrect but its hard to say if it's the only problem without seeing all your code. Rather than using @Input('date') declare the date property like so: private _date: string;. Also, make sure you are instantiating the model with the new keyword. Lastly, access the property using regular dot notation.
Check your work against this example from https://www.typescriptlang.org/docs/handbook/classes.html :
let passcode = "secret passcode";
class Employee {
private _fullName: string;
get fullName(): string {
return this._fullName;
}
set fullName(newName: string) {
if (passcode && passcode == "secret passcode") {
this._fullName = newName;
}
else {
console.log("Error: Unauthorized update of employee!");
}
}
}
let employee = new Employee();
employee.fullName = "Bob Smith";
if (employee.fullName) {
console.log(employee.fullName);
}
And here is a plunker demonstrating what it sounds like you're trying to do: https://plnkr.co/edit/OUoD5J1lfO6bIeME9N0F?p=preview
How can I force Python's file.write() to use the same newline format in Windows as in Linux ("\r\n" vs. "\n")?
You need to open the file in binary mode i.e. wb instead of w. If you don't, the end of line characters are auto-converted to OS specific ones.
Here is an excerpt from Python reference about open().
The default is to use text mode, which may convert '\n' characters to a platform-specific representation on writing and back on reading.
Convert UNIX epoch to Date object
Go via POSIXct and you want to set a TZ there -- here you see my (Chicago) default:
R> val <- 1352068320
R> as.POSIXct(val, origin="1970-01-01")
[1] "2012-11-04 22:32:00 CST"
R> as.Date(as.POSIXct(val, origin="1970-01-01"))
[1] "2012-11-05"
R>
Edit: A few years later, we can now use the anytime package:
R> library(anytime)
R> anytime(1352068320)
[1] "2012-11-04 16:32:00 CST"
R> anydate(1352068320)
[1] "2012-11-04"
R>
Note how all this works without any format or origin arguments.
How to change the map center in Leaflet.js
Use map.panTo(); does not do anything if the point is in the current view. Use map.setView() instead.
I had a polyline and I had to center map to a new point in polyline at every second. Check the code : GOOD: https://jsfiddle.net/nstudor/xcmdwfjk/
mymap.setView(point, 11, { animation: true });
BAD: https://jsfiddle.net/nstudor/Lgahv905/
mymap.panTo(point);
mymap.setZoom(11);
Full Screen Theme for AppCompat
This theme only works after API 21(included). And make both the StatusBar and NavigationBar transparent.
<style name="TransparentAppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
<item name="windowActionBar">false</item>
<item name="windowNoTitle">true</item>
<item name="android:statusBarColor">@android:color/transparent</item>
<item name="android:windowBackground">@android:color/transparent</item>
<item name="android:navigationBarColor">@android:color/transparent</item>
<item name="android:windowIsTranslucent">true</item>
<item name="android:windowContentOverlay">@null</item>
</style>
Multiple linear regression in Python
You can use the function below and pass it a DataFrame:
def linear(x, y=None, show=True):
"""
@param x: pd.DataFrame
@param y: pd.DataFrame or pd.Series or None
if None, then use last column of x as y
@param show: if show regression summary
"""
import statsmodels.api as sm
xy = sm.add_constant(x if y is None else pd.concat([x, y], axis=1))
res = sm.OLS(xy.ix[:, -1], xy.ix[:, :-1], missing='drop').fit()
if show: print res.summary()
return res
Angular 2 change event - model changes
That's a known issue. Currently you have to use a workaround like shown in your question.
This is working as intended. When the change event is emitted ngModelChange (the (...) part of [(ngModel)] hasn't updated the bound model yet:
<input type="checkbox" (ngModelChange)="myModel=$event" [ngModel]="mymodel">
See also
What does "The following object is masked from 'package:xxx'" mean?
I have the same problem. I avoid it with remove.packages("Package making this confusion") and it works. In my case, I don't need the second package, so that is not a very good idea.
angular 2 sort and filter
This is my sort. It will do number sort , string sort and date sort .
import { Pipe , PipeTransform } from "@angular/core";
@Pipe({
name: 'sortPipe'
})
export class SortPipe implements PipeTransform {
transform(array: Array<string>, key: string): Array<string> {
console.log("Entered in pipe******* "+ key);
if(key === undefined || key == '' ){
return array;
}
var arr = key.split("-");
var keyString = arr[0]; // string or column name to sort(name or age or date)
var sortOrder = arr[1]; // asc or desc order
var byVal = 1;
array.sort((a: any, b: any) => {
if(keyString === 'date' ){
let left = Number(new Date(a[keyString]));
let right = Number(new Date(b[keyString]));
return (sortOrder === "asc") ? right - left : left - right;
}
else if(keyString === 'name'){
if(a[keyString] < b[keyString]) {
return (sortOrder === "asc" ) ? -1*byVal : 1*byVal;
} else if (a[keyString] > b[keyString]) {
return (sortOrder === "asc" ) ? 1*byVal : -1*byVal;
} else {
return 0;
}
}
else if(keyString === 'age'){
return (sortOrder === "asc") ? a[keyString] - b[keyString] : b[keyString] - a[keyString];
}
});
return array;
}
}
How to convert comma-separated String to List?
List<String> items = Arrays.asList(commaSeparated.split(","));
That should work for you.
How to generate the JPA entity Metamodel?
Ok, based on what I have read here, I did it with EclipseLink this way and I did not need to put the processor dependency to the project, only as an annotationProcessorPath element of the compiler plugin.
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<annotationProcessorPaths>
<annotationProcessorPath>
<groupId>org.eclipse.persistence</groupId>
<artifactId>org.eclipse.persistence.jpa.modelgen.processor</artifactId>
<version>2.7.7</version>
</annotationProcessorPath>
</annotationProcessorPaths>
<compilerArgs>
<arg>-Aeclipselink.persistencexml=src/main/resources/META-INF/persistence.xml</arg>
</compilerArgs>
</configuration>
</plugin>
Some dates recognized as dates, some dates not recognized. Why?
In your case it is probably taking them in DD-MM-YY format, not MM-DD-YY.
element with the max height from a set of elements
var maxHeight = Math.max.apply(null, $("div.panel").map(function ()
{
return $(this).height();
}).get());
If that's confusing to read, this might be clearer:
var heights = $("div.panel").map(function ()
{
return $(this).height();
}).get();
maxHeight = Math.max.apply(null, heights);
TypeError: Can't convert 'int' object to str implicitly
You cannot concatenate a string with an int. You would need to convert your int to a string using the str function, or use formatting to format your output.
Change: -
print("Ok. Your balance is now at " + balanceAfterStrength + " skill points.")
to: -
print("Ok. Your balance is now at {} skill points.".format(balanceAfterStrength))
or: -
print("Ok. Your balance is now at " + str(balanceAfterStrength) + " skill points.")
or as per the comment, use , to pass different strings to your print function, rather than concatenating using +: -
print("Ok. Your balance is now at ", balanceAfterStrength, " skill points.")
Why do table names in SQL Server start with "dbo"?
dbo is the default schema in SQL Server. You can create your own schemas to allow you to better manage your object namespace.
What is the JavaScript equivalent of var_dump or print_r in PHP?
Most modern browsers have a console in their developer tools, useful for this sort of debugging.
console.log(myvar);
Then you will get a nicely mapped out interface of the object/whatever in the console.
Check out the console documentation for more details.
Map implementation with duplicate keys
If there are duplicate keys then a key may correspond to more than one value. The obvious solution is to map the key to a list of these values.
For example in Python:
map = dict()
map["driver"] = list()
map["driver"].append("john")
map["driver"].append("mike")
print map["driver"] # It shows john and mike
print map["driver"][0] # It shows john
print map["driver"][1] # It shows mike
How to use std::sort to sort an array in C++
sorting method without std::sort:
// sorting myArray ascending
int iTemp = 0;
for (int i = 0; i < ARRAYSIZE; i++)
{
for (int j = i + 1; j <= ARRAYSIZE; j++)
{
// for descending sort change '<' with '>'
if (myArray[j] < myArray[i])
{
iTemp = myArray[i];
myArray[i] = myArray[j];
myArray[j] = iTemp;
}
}
}
Run complete example:
#include <iostream> // std::cout, std::endl /* http://en.cppreference.com/w/cpp/header/iostream */
#include <cstdlib> // srand(), rand() /* http://en.cppreference.com/w/cpp/header/cstdlib */
#include <ctime> // time() /* http://en.cppreference.com/w/cpp/header/ctime */
int main()
{
const int ARRAYSIZE = 10;
int myArray[ARRAYSIZE];
// populate myArray with random numbers from 1 to 1000
srand(time(0));
for (int i = 0; i < ARRAYSIZE; i++)
{
myArray[i] = rand()% 1000 + 1;
}
// print unsorted myArray
std::cout << "unsorted myArray: " << std::endl;
for (int i = 0; i < ARRAYSIZE; i++)
{
std::cout << "[" << i << "] -> " << myArray[i] << std::endl;
}
std::cout << std::endl;
// sorting myArray ascending
int iTemp = 0;
for (int i = 0; i < ARRAYSIZE; i++)
{
for (int j = i + 1; j <= ARRAYSIZE; j++)
{
// for descending sort change '<' with '>'
if (myArray[j] < myArray[i])
{
iTemp = myArray[i];
myArray[i] = myArray[j];
myArray[j] = iTemp;
}
}
}
// print sorted myArray
std::cout << "sorted myArray: " << std::endl;
for (int i = 0; i < ARRAYSIZE; i++)
{
std::cout << "[" << i << "] -> " << myArray[i] << std::endl;
}
std::cout << std::endl;
return 0;
}
How do you convert between 12 hour time and 24 hour time in PHP?
// 24-hour time to 12-hour time
$time_in_12_hour_format = date("g:i a", strtotime("13:30"));
// 12-hour time to 24-hour time
$time_in_24_hour_format = date("H:i", strtotime("1:30 PM"));
Redirect from asp.net web api post action
Here is another way you can get to the root of your website without hard coding the url:
var response = Request.CreateResponse(HttpStatusCode.Moved);
string fullyQualifiedUrl = Request.RequestUri.GetLeftPart(UriPartial.Authority);
response.Headers.Location = new Uri(fullyQualifiedUrl);
Note: Will only work if both your MVC website and WebApi are on the same URL
AngularJS - $http.post send data as json
Use JSON.stringify() to wrap your json
var parameter = JSON.stringify({type:"user", username:user_email, password:user_password});
$http.post(url, parameter).
success(function(data, status, headers, config) {
// this callback will be called asynchronously
// when the response is available
console.log(data);
}).
error(function(data, status, headers, config) {
// called asynchronously if an error occurs
// or server returns response with an error status.
});
Why do 64-bit DLLs go to System32 and 32-bit DLLs to SysWoW64 on 64-bit Windows?
I should add: You should not be putting your dll's into \system32\ anyway! Modify your code, modify your installer... find a home for your bits that is NOT anywhere under c:\windows\
For example, your installer puts your dlls into:
\program files\<your app dir>\
or
\program files\common files\<your app name>\
(Note: The way you actually do this is to use the environment var: %ProgramFiles% or %ProgramFiles(x86)% to find where Program Files is.... you do not assume it is c:\program files\ ....)
and then sets a registry tag :
HKLM\software\<your app name>
-- dllLocation
The code that uses your dlls reads the registry, then dynamically links to the dlls in that location.
The above is the smart way to go.
You do not ever install your dlls, or third party dlls into \system32\ or \syswow64. If you have to statically load, you put your dlls in your exe dir (where they will be found). If you cannot predict the exe dir (e.g. some other exe is going to call your dll), you may have to put your dll dir into the search path (avoid this if at all poss!)
system32 and syswow64 are for Windows provided files... not for anyone elses files. The only reason folks got into the bad habit of putting stuff there is because it is always in the search path, and many apps/modules use static linking. (So, if you really get down to it, the real sin is static linking -- this is a sin in native code and managed code -- always always always dynamically link!)
Output PowerShell variables to a text file
Use this:
"$computer, $Speed, $Regcheck" | out-file -filepath C:\temp\scripts\pshell\dump.txt -append -width 200
Why do you need to put #!/bin/bash at the beginning of a script file?
The shebang is a directive to the loader to use the program which is specified after the #! as the interpreter for the file in question when you try to execute it. So, if you try to run a file called foo.sh which has #!/bin/bash at the top, the actual command that runs is /bin/bash foo.sh. This is a flexible way of using different interpreters for different programs. This is something implemented at the system level and the user level API is the shebang convention.
It's also worth knowing that the shebang is a magic number - a human readable one that identifies the file as a script for the given interpreter.
Your point about it "working" even without the shebang is only because the program in question is a shell script written for the same shell as the one you are using. For example, you could very well write a javascript file and then put a #! /usr/bin/js (or something similar) to have a javascript "Shell script".
How to make rpm auto install dependencies
Simple just run the following command.
sudo dnf install *package.rpm
Enter your password and you are done.
/usr/lib/libstdc++.so.6: version `GLIBCXX_3.4.15' not found
I've had a similar issue, and I've resolved it by statically linking libstdc++ into the program I was compiling, like so:
$ LIBS=-lstdc++ ./configure ... etc.
instead of the usual
$ ./configure ... etc.
There might be problems with this solution to do with loading shared libraries at runtime, but I haven't looked into the issue deeply enough to comment.
How to print color in console using System.out.println?
Using color function to print text with colors
Code:
enum Color {
RED("\033[0;31m"), // RED
GREEN("\033[0;32m"), // GREEN
YELLOW("\033[0;33m"), // YELLOW
BLUE("\033[0;34m"), // BLUE
MAGENTA("\033[0;35m"), // MAGENTA
CYAN("\033[0;36m"), // CYAN
private final String code
Color(String code) {
this.code = code;
}
@Override
String toString() {
return code
}
}
def color = { color, txt ->
def RESET_COLOR = "\033[0m"
return "${color}${txt}${RESET_COLOR}"
}
Usage:
test {
println color(Color.CYAN, 'testing')
}
DB2 SQL error: SQLCODE: -206, SQLSTATE: 42703
That only means that an undefined column or parameter name was detected. The errror that DB2 gives should point what that may be:
DB2 SQL Error: SQLCODE=-206, SQLSTATE=42703, SQLERRMC=[THE_UNDEFINED_COLUMN_OR_PARAMETER_NAME], DRIVER=4.8.87
Double check your table definition. Maybe you just missed adding something.
I also tried google-ing this problem and saw this:
http://www.coderanch.com/t/515475/JDBC/databases/sql-insert-statement-giving-sqlcode
Difference between dangling pointer and memory leak
You can think of these as the opposites of one another.
When you free an area of memory, but still keep a pointer to it, that pointer is dangling:
char *c = malloc(16);
free(c);
c[1] = 'a'; //invalid access through dangling pointer!
When you lose the pointer, but keep the memory allocated, you have a memory leak:
void myfunc()
{
char *c = malloc(16);
} //after myfunc returns, the the memory pointed to by c is not freed: leak!
What does double question mark (??) operator mean in PHP
It's the "null coalescing operator", added in php 7.0. The definition of how it works is:
It returns its first operand if it exists and is not NULL; otherwise it returns its second operand.
So it's actually just isset() in a handy operator.
Those two are equivalent1:
$foo = $bar ?? 'something';
$foo = isset($bar) ? $bar : 'something';
Documentation: http://php.net/manual/en/language.operators.comparison.php#language.operators.comparison.coalesce
In the list of new PHP7 features: http://php.net/manual/en/migration70.new-features.php#migration70.new-features.null-coalesce-op
And original RFC https://wiki.php.net/rfc/isset_ternary
EDIT: As this answer gets a lot of views, little clarification:
1There is a difference: In case of ??, the first expression is evaluated only once, as opposed to ? :, where the expression is first evaluated in the condition section, then the second time in the "answer" section.
Is java.sql.Timestamp timezone specific?
Although it is not explicitly specified for setTimestamp(int parameterIndex, Timestamp x) drivers have to follow the rules established by the setTimestamp(int parameterIndex, Timestamp x, Calendar cal) javadoc:
Sets the designated parameter to the given
java.sql.Timestampvalue, using the givenCalendarobject. The driver uses theCalendarobject to construct an SQLTIMESTAMPvalue, which the driver then sends to the database. With aCalendarobject, the driver can calculate the timestamp taking into account a custom time zone. If noCalendarobject is specified, the driver uses the default time zone, which is that of the virtual machine running the application.
When you call with setTimestamp(int parameterIndex, Timestamp x) the JDBC driver uses the time zone of the virtual machine to calculate the date and time of the timestamp in that time zone. This date and time is what is stored in the database, and if the database column does not store time zone information, then any information about the zone is lost (which means it is up to the application(s) using the database to use the same time zone consistently or come up with another scheme to discern timezone (ie store in a separate column).
For example: Your local time zone is GMT+2. You store "2012-12-25 10:00:00 UTC". The actual value stored in the database is "2012-12-25 12:00:00". You retrieve it again: you get it back again as "2012-12-25 10:00:00 UTC" (but only if you retrieve it using getTimestamp(..)), but when another application accesses the database in time zone GMT+0, it will retrieve the timestamp as "2012-12-25 12:00:00 UTC".
If you want to store it in a different timezone, then you need to use the setTimestamp(int parameterIndex, Timestamp x, Calendar cal) with a Calendar instance in the required timezone. Just make sure you also use the equivalent getter with the same time zone when retrieving values (if you use a TIMESTAMP without timezone information in your database).
So, assuming you want to store the actual GMT timezone, you need to use:
Calendar cal = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
stmt.setTimestamp(11, tsSchedStartTime, cal);
With JDBC 4.2 a compliant driver should support java.time.LocalDateTime (and java.time.LocalTime) for TIMESTAMP (and TIME) through get/set/updateObject. The java.time.Local* classes are without time zones, so no conversion needs to be applied (although that might open a new set of problems if your code did assume a specific time zone).
How to suppress Pandas Future warning ?
Warnings are annoying. As mentioned in other answers, you can suppress them using:
import warnings
warnings.simplefilter(action='ignore', category=FutureWarning)
But if you want to handle them one by one and you are managing a bigger codebase, it will be difficult to find the line of code which is causing the warning. Since warnings unlike errors don't come with code traceback. In order to trace warnings like errors, you can write this at the top of the code:
import warnings
warnings.filterwarnings("error")
But if the codebase is bigger and it is importing bunch of other libraries/packages, then all sort of warnings will start to be raised as errors. In order to raise only certain type of warnings (in your case, its FutureWarning) as error, you can write:
import warnings
warnings.simplefilter(action='error', category=FutureWarning)
How to get row number from selected rows in Oracle
There is no inherent ordering to a table. So, the row number itself is a meaningless metric.
However, you can get the row number of a result set by using the ROWNUM psuedocolumn or the ROW_NUMBER() analytic function, which is more powerful.
As there is no ordering to a table both require an explicit ORDER BY clause in order to work.
select rownum, a.*
from ( select *
from student
where name like '%ram%'
order by branch
) a
or using the analytic query
select row_number() over ( order by branch ) as rnum, a.*
from student
where name like '%ram%'
Your syntax where name is like ... is incorrect, there's no need for the IS, so I've removed it.
The ORDER BY here relies on a binary sort, so if a branch starts with anything other than B the results may be different, for instance b is greater than B.
Get day of week in SQL Server 2005/2008
SELECT CASE DATEPART(WEEKDAY,GETDATE())
WHEN 1 THEN 'SUNDAY'
WHEN 2 THEN 'MONDAY'
WHEN 3 THEN 'TUESDAY'
WHEN 4 THEN 'WEDNESDAY'
WHEN 5 THEN 'THURSDAY'
WHEN 6 THEN 'FRIDAY'
WHEN 7 THEN 'SATURDAY'
END
How to shutdown my Jenkins safely?
You can kill Jenkins safely. It will catch SIGTERM and SIGINT and perform an orderly shutdown. However, if Jenkins was in the middle of building something, it will abort the builds and they will show up gray in the status display.
If you want to avoid this, you must put Jenkins into shutdown mode to prevent it from starting new builds and wait until currently running builds are done before killing Jenkins.
You can also use the Jenkins command line interface and tell Jenkins to safe-shutdown, which does the same. You can find more info on Jenkins cli at http://YOURJENKINS/cli
ASP.NET MVC: Html.EditorFor and multi-line text boxes
Use data type 'MultilineText':
[DataType(DataType.MultilineText)]
public string Text { get; set; }
ACCESS_FINE_LOCATION AndroidManifest Permissions Not Being Granted
I was having the same problem and could not figure out what I was doing wrong. Turns out, the auto-complete for Android Studio was changing the text to either all caps or all lower case (depending on whether I typed in upper case or lower cast words before the auto-complete). The OS was not registering the name due to this issue and I would get the error regarding a missing permission. As stated above, ensure your permissions are labeled correctly:
Correct:
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
Incorrect:
<uses-permission android:name="ANDROID.PERMISSION.ACCESS_FINE_LOCATION" />
Incorrect:
<uses-permission android:name="android.permission.access_fine_location" />
Though this may seem trivial, its easy to overlook.
If there is some setting to make permissions non-case-sensitive, please add a comment with the instructions. Thank you!
Overriding !important style
Rather than injecting style, if you inject a class(for eg: 'show') through java script, it will work. But here you need css like below. the added class css rule should be below your original rule.
td.EvenRow a{
display: none !important;
}
td.EvenRow a.show{
display: block !important;
}
Apache: Restrict access to specific source IP inside virtual host
The mod_authz_host directives need to be inside a <Location> or <Directory> block but I've used the former within <VirtualHost> like so for Apache 2.2:
<VirtualHost *:8080>
<Location />
Order deny,allow
Deny from all
Allow from 127.0.0.1
</Location>
...
</VirtualHost>
Reference: https://askubuntu.com/questions/262981/how-to-install-mod-authz-host-in-apache
How to include an HTML page into another HTML page without frame/iframe?
You can say that it is with PHP, but actually it has just one PHP command, all other files are just *.html.
- You should have a file named .htaccess in your web server's /public_html directory, or in another directory, where your html file will be and you will process one command inside it.
- If you do not have it, (or it might be hidden (you should check this directory list by checking directory for hidden files)), you can create it with notepad, and just type one row in it:
AddType application/x-httpd-php .html - Save this file with the name .htaccess and upload it to the server's main directory.
- In your html file anywhere you want an external "meniu.html file to appear, add te command:
<?php include("meniu.html"); ?>.
That's all!
Remark: all commands like <? ...> will be treated as php executables, so if your html have question marks, then you could have some problems.
How to select multiple rows filled with constants?
select (level - 1) * row_dif + 1 as a, (level - 1) * row_dif + 2 as b, (level - 1) * row_dif + 3 as c
from dual
connect by level <= number_of_rows;
something like that
select (level - 1) * 3 + 1 as a, (level - 1) * 3 + 2 as b, (level - 1) * 3 + 3 as c
from dual
connect by level <= 3;
MySQL - How to parse a string value to DATETIME format inside an INSERT statement?
Use MySQL's STR_TO_DATE() function to parse the string that you're attempting to insert:
INSERT INTO tblInquiry (fldInquiryReceivedDateTime) VALUES
(STR_TO_DATE('5/15/2012 8:06:26 AM', '%c/%e/%Y %r'))
Why am I getting 'Assembly '*.dll' must be strong signed in order to be marked as a prerequisite.'?
Is your assembly properly signed?
To check this, press Alt+Enter on your project (or right click, then Properties). Go to "Signing". Verify that the check box "Sign the assembly" is checked and the strong name key file is selected and "Delay sign only" is unchecked.
Python error "ImportError: No module named"
On *nix, also make sure that PYTHONPATH is configured correctly, especially that it has this format:
.:/usr/local/lib/python
(Mind the .: at the beginning, so that it can search on the current directory, too.)
It may also be in other locations, depending on the version:
.:/usr/lib/python
.:/usr/lib/python2.6
.:/usr/lib/python2.7 and etc.
How to use SVG markers in Google Maps API v3
Yes you can use an .svg file for the icon just like you can .png or another image file format. Just set the url of the icon to the directory where the .svg file is located. For example:
var icon = {
url: 'path/to/images/car.svg',
size: new google.maps.Size(sizeX, sizeY),
origin: new google.maps.Point(0, 0),
anchor: new google.maps.Point(sizeX/2, sizeY/2)
};
var marker = new google.maps.Marker({
position: event.latLng,
map: map,
draggable: false,
icon: icon
});
How to run certain task every day at a particular time using ScheduledExecutorService?
What if your server goes down at 4:59AM and comes back at 5:01AM? I think it will just skip the run. I would recommend persistent scheduler like Quartz, that would store its schedule data somewhere. Then it will see that this run hasn't been performed yet and will do it at 5:01AM.
Directing print output to a .txt file
Give print a file keyword argument, where the value of the argument is a file stream. We can create a file stream using the open function:
print("Hello stackoverflow!", file=open("output.txt", "a"))
print("I have a question.", file=open("output.txt", "a"))
From the Python documentation about print:
The
fileargument must be an object with awrite(string)method; if it is not present orNone,sys.stdoutwill be used.
And the documentation for open:
Open
fileand return a corresponding file object. If the file cannot be opened, anOSErroris raised.
The "a" as the second argument of open means "append" - in other words, the existing contents of the file won't be overwritten. If you want the file to be overwritten instead, use "w".
Opening a file with open many times isn't ideal for performance, however. You should ideally open it once and name it, then pass that variable to print's file option. You must remember to close the file afterwards!
f = open("output.txt", "a")
print("Hello stackoverflow!", file=f)
print("I have a question.", file=f)
f.close()
There's also a syntactic shortcut for this, which is the with block. This will close your file at the end of the block for you:
with open("output.txt", "a") as f:
print("Hello stackoverflow!", file=f)
print("I have a question.", file=f)
When you use 'badidea' or 'thisisunsafe' to bypass a Chrome certificate/HSTS error, does it only apply for the current site?
I'm a PHP developer and to be able to work on my development environment with a certificate, I was able to do the same by finding the real SSL HTTPS/HTTP Certificate and deleting it.
The steps are :
- In the address bar, type "chrome://net-internals/#hsts".
- Type the domain name in the text field below "Delete domain".
- Click the "Delete" button.
- Type the domain name in the text field below "Query domain".
- Click the "Query" button.
- Your response should be "Not found".
You can find more information at : http://classically.me/blogs/how-clear-hsts-settings-major-browsers
Although this solution is not the best, Chrome currently does not have any good solution for the moment. I have escalated this situation with their support team to help improve user experience.
Edit : you have to repeat the steps every time you will go on the production site.
How to access environment variable values?
import os
for a in os.environ:
print('Var: ', a, 'Value: ', os.getenv(a))
print("all done")
That will print all of the environment variables along with their values.
How do I loop through a date range?
For your example you can try
DateTime StartDate = new DateTime(2009, 3, 10);
DateTime EndDate = new DateTime(2009, 3, 26);
int DayInterval = 3;
List<DateTime> dateList = new List<DateTime>();
while (StartDate.AddDays(DayInterval) <= EndDate)
{
StartDate = StartDate.AddDays(DayInterval);
dateList.Add(StartDate);
}
Reverse engineering from an APK file to a project
Yes, you can get your project back. Just rename the yourproject.apk file to yourproject.zip, and you will get all the files inside that ZIP file. We are changing the file extension from .apk to .zip. From that ZIP file, extract the classes.dex file and decompile it by following way.
First, you need a tool to extract all the (compiled) classes on the DEX to a JAR. There's one called dex2jar, which is made by a Chinese student.
Then, you can use JD-GUI to decompile the classes in the JAR to source code. The resulting source code should be quite readable, as dex2jar applies some optimizations.
How to add not null constraint to existing column in MySQL
Try this, you will know the difference between change and modify,
ALTER TABLE table_name CHANGE curr_column_name new_column_name new_column_datatype [constraints]
ALTER TABLE table_name MODIFY column_name new_column_datatype [constraints]
- You can change name and datatype of the particular column using
CHANGE. - You can modify the particular column datatype using
MODIFY. You cannot change the name of the column using this statement.
Hope, I explained well in detail.
Can I perform a DNS lookup (hostname to IP address) using client-side Javascript?
There's no notion of hosts or ip-addresses in the javascript standard library. So you'll have to access some external service to look up hostnames for you.
I recommend hosting a cgi-bin which looks up the ip-address of a hostname and access that via javascript.
How to resolve TypeError: can only concatenate str (not "int") to str
instead of using " + " operator
print( "Alireza" + 1980)
Use comma " , " operator
print( "Alireza" , 1980)
Parse rfc3339 date strings in Python?
This has already been answered here: How do I translate a ISO 8601 datetime string into a Python datetime object?
d = datetime.datetime.strptime( "2012-10-09T19:00:55Z", "%Y-%m-%dT%H:%M:%SZ" )
d.weekday()
ERROR Could not load file or assembly 'AjaxControlToolkit' or one of its dependencies
Just Add AjaxControlToolkit.dll to your Reference folder.
On your Project Solution
Right Click on Reference Folder > Add Reference > browse AjaxControlToolkit.dll .
Then build.
Regards
How to get status code from webclient?
Tried it out. ResponseHeaders do not include status code.
If I'm not mistaken, WebClient is capable of abstracting away multiple distinct requests in a single method call (e.g. correctly handling 100 Continue responses, redirects, and the like). I suspect that without using HttpWebRequest and HttpWebResponse, a distinct status code may not be available.
It occurs to me that, if you are not interested in intermediate status codes, you can safely assume the final status code is in the 2xx (successful) range, otherwise, the call would not be successful.
The status code unfortunately isn't present in the ResponseHeaders dictionary.
Angular JS - angular.forEach - How to get key of the object?
var obj = {name: 'Krishna', gender: 'male'};
angular.forEach(obj, function(value, key) {
console.log(key + ': ' + value);
});
yields the attributes of obj with their respective values:
name: Krishna
gender: male
Stop MySQL service windows
This is a newer and easier answer.
- Run cmd as admin
- Type "net start mysql" then the version number, in my case "net start mysql80" for MySQL 8.0.
- If it says it's already running great, otherwise now mysql is running.
- Exit cmd, WIN+R and type services.msc, scroll down until you find my sql with the right version.
- Right-Click for properties, under startup type select 'Manual', then under service status select 'Stop'
- Now you stopped mysql service and it will not run automatically again.
- To turn it back on, in cmd admin 'net start mysql' and the version number, in my case 'net start mysql80'
How to resolve "could not execute statement; SQL [n/a]; constraint [numbering];"?
Hibernate tries to insert data that violate underlying database integrity contraints.
There's probably misconfiguration in hibernate persistent classes and/or mapping configuration (*.hbm.xml or annotations in persitent classes).
Maybe a property of the bean you want to save is not type-compatible with its related field in database (could explain the constraint [numbering] part).
Error in Eclipse: "The project cannot be built until build path errors are resolved"
If not working in any case...then delete your project from the Eclipse workspace and again import as a Maven project if that is a Maven project. Else import as an existing project.
I tried all the previous given solutions, but they didn't work, but it works for me.
PHP substring extraction. Get the string before the first '/' or the whole string
What about this :
substr($mystring.'/', 0, strpos($mystring, '/'))
Simply add a '/' to the end of mystring so you can be sure there is at least one ;)
This could be due to the service endpoint binding not using the HTTP protocol
I had this problem because I configured my WCF Service to return a System.Data.DataTable.
It worked fine in my test HTML page, but blew up when I put this in my Windows Form application.
I had to go in and change the Service's Operational Contract signature from DataTable to DataSet and return the data accordingly.
If you have this problem, you may want to add an additional Operational Contract to your Service so you do not have to worry about breaking code that rely on existing Services.
html5 audio player - jquery toggle click play/pause?
Because Firefox does not support mp3 format. To make this work with Firefox, you should use the ogg format.
Confusing "duplicate identifier" Typescript error message
You could also use the exclude option in tsconfig.json file like so:
{
"compilerOptions": {
"target": "es5",
"module": "commonjs",
"declaration": false,
"noImplicitAny": false,
"removeComments": true,
"noLib": false,
"emitDecoratorMetadata": true,
"experimentalDecorators": true
},
"exclude": [
"node_modules"
]
}
Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.2:java (default-cli)
I had a similar problem.
As it turned out, I ran mvn clean package install.
Correct way is mvn clean install
SQL subquery with COUNT help
SELECT e.*,
cnt.colCount
FROM eventsTable e
INNER JOIN (
select columnName,count(columnName) as colCount
from eventsTable e2
group by columnName
) as cnt on cnt.columnName = e.columnName
WHERE e.columnName='Business'
-- Added space
problem with php mail 'From' header
I solved this by adding email accounts in Cpanel and also adding that same email to the header from field like this
$header = 'From: XXXXXXXX <[email protected]>' . "\r\n";
Easy way to password-protect php page
Not the solution, but for your interest: HTTP authentication only works, when PHP runs as Apache module. Most hosters provide PHP as CGI version only.
How to append rows in a pandas dataframe in a for loop?
There are 2 reasons you may append rows in a loop, 1. add to an existing df, and 2. create a new df.
to create a new df, I think its well documented that you should either create your data as a list and then create the data frame:
cols = ['c1', 'c2', 'c3']
lst = []
for a in range(2):
lst.append([1, 2, 3])
df1 = pd.DataFrame(lst, columns=cols)
df1
Out[3]:
c1 c2 c3
0 1 2 3
1 1 2 3
OR, Create the dataframe with an index and then add to it
cols = ['c1', 'c2', 'c3']
df2 = pd.DataFrame(columns=cols, index=range(2))
for a in range(2):
df2.loc[a].c1 = 4
df2.loc[a].c2 = 5
df2.loc[a].c3 = 6
df2
Out[4]:
c1 c2 c3
0 4 5 6
1 4 5 6
If you want to add to an existing dataframe, you could use either method above and then append the df's together (with or without the index):
df3 = df2.append(df1, ignore_index=True)
df3
Out[6]:
c1 c2 c3
0 4 5 6
1 4 5 6
2 1 2 3
3 1 2 3
Or, you can also create a list of dictionary entries and append those as in the answer above.
lst_dict = []
for a in range(2):
lst_dict.append({'c1':2, 'c2':2, 'c3': 3})
df4 = df1.append(lst_dict)
df4
Out[7]:
c1 c2 c3
0 1 2 3
1 1 2 3
0 2 2 3
1 2 2 3
Using the dict(zip(cols, vals)))
lst_dict = []
for a in range(2):
vals = [7, 8, 9]
lst_dict.append(dict(zip(cols, vals)))
df5 = df1.append(lst_dict)
How do I add a new column to a Spark DataFrame (using PySpark)?
To add a column using a UDF:
df = sqlContext.createDataFrame(
[(1, "a", 23.0), (3, "B", -23.0)], ("x1", "x2", "x3"))
from pyspark.sql.functions import udf
from pyspark.sql.types import *
def valueToCategory(value):
if value == 1: return 'cat1'
elif value == 2: return 'cat2'
...
else: return 'n/a'
# NOTE: it seems that calls to udf() must be after SparkContext() is called
udfValueToCategory = udf(valueToCategory, StringType())
df_with_cat = df.withColumn("category", udfValueToCategory("x1"))
df_with_cat.show()
## +---+---+-----+---------+
## | x1| x2| x3| category|
## +---+---+-----+---------+
## | 1| a| 23.0| cat1|
## | 3| B|-23.0| n/a|
## +---+---+-----+---------+
Get difference between two dates in months using Java
You can use Joda time library for Java. It would be much easier to calculate time-diff between dates with it.
Sample snippet for time-diff:
Days d = Days.daysBetween(startDate, endDate);
int days = d.getDays();
Authentication versus Authorization
Authentication is the process of verifying the proclaimed identity.
- e.g. username/password
Usually followed by authorization, which is the approval that you can do this and that.
- e.g. permissions
Check if decimal value is null
Assuming you are reading from a data row, what you want is:
if ( !rdrSelect.IsNull(23) )
{
//handle parsing
}
Centering image and text in R Markdown for a PDF report
You can set the center (or other) alignment for the whole document as a Knitr option, using:
knitr::opts_chunk$set(echo = TRUE, fig.align="center")
Get host domain from URL?
WWW is an alias, so you don't need it if you want a domain. Here is my litllte function to get the real domain from a string
private string GetDomain(string url)
{
string[] split = url.Split('.');
if (split.Length > 2)
return split[split.Length - 2] + "." + split[split.Length - 1];
else
return url;
}
Multiple distinct pages in one HTML file
Well, you could, but you probably just want to have two sets of content in the same page, and switch between them. Example:
<html>
<head>
<script>
function show(shown, hidden) {
document.getElementById(shown).style.display='block';
document.getElementById(hidden).style.display='none';
return false;
}
</script>
</head>
<body>
<div id="Page1">
Content of page 1
<a href="#" onclick="return show('Page2','Page1');">Show page 2</a>
</div>
<div id="Page2" style="display:none">
Content of page 2
<a href="#" onclick="return show('Page1','Page2');">Show page 1</a>
</div>
</body>
</html>(Simplififed HTML code, should of course have doctype, etc.)
Clear a terminal screen for real
None of the answers I read worked in PuTTY, so I found a comment on this article:
In the settings for your connection, under "Window->Behavior" you'll find a setting "System Menu Appears on ALT alone". Then CTRL + L, ALT, l (that's a lower case L) will scroll the screen and then clear the scrollback buffer.
(relevant to the OP because I am connecting to an Ubuntu server, but also apparently relevant no matter what your server is running.)
How to force JS to do math instead of putting two strings together
DON'T FORGET - Use parseFloat(); if your dealing with decimals.
Bootstrap 3.0 Sliding Menu from left
Probably late but here is a plugin that can do the job : http://multi-level-push-menu.make.rs/
Also v2 can use mobile gesture such as swipe ;)
Bootstrap tab activation with JQuery
Add an id attribute to a html tag
<ul class="nav nav-tabs">
<li><a href="#aaa" data-toggle="tab" id="tab_aaa">AAA</a></li>
<li><a href="#bbb" data-toggle="tab" id="tab_bbb">BBB</a></li>
<li><a href="#ccc" data-toggle="tab" id="tab_ccc">CCC</a></li>
</ul>
<div class="tab-content" id="tabs">
<div class="tab-pane" id="aaa">...Content...</div>
<div class="tab-pane" id="bbb">...Content...</div>
<div class="tab-pane" id="ccc">...Content...</div>
</div>
Then using JQuery
$("#tab_aaa").tab('show');
Can I set max_retries for requests.request?
This will not only change the max_retries but also enable a backoff strategy which makes requests to all http:// addresses sleep for a period of time before retrying (to a total of 5 times):
import requests
from urllib3.util.retry import Retry
from requests.adapters import HTTPAdapter
s = requests.Session()
retries = Retry(total=5,
backoff_factor=0.1,
status_forcelist=[ 500, 502, 503, 504 ])
s.mount('http://', HTTPAdapter(max_retries=retries))
s.get('http://httpstat.us/500')
As per documentation for Retry: if the backoff_factor is 0.1, then sleep() will sleep for [0.1s, 0.2s, 0.4s, ...] between retries. It will also force a retry if the status code returned is 500, 502, 503 or 504.
Various other options to Retry allow for more granular control:
- total – Total number of retries to allow.
- connect – How many connection-related errors to retry on.
- read – How many times to retry on read errors.
- redirect – How many redirects to perform.
- method_whitelist – Set of uppercased HTTP method verbs that we should retry on.
- status_forcelist – A set of HTTP status codes that we should force a retry on.
- backoff_factor – A backoff factor to apply between attempts.
- raise_on_redirect – Whether, if the number of redirects is exhausted, to raise a
MaxRetryError, or to return a response with a response code in the 3xx range. - raise_on_status – Similar meaning to raise_on_redirect: whether we should raise an exception, or return a response, if status falls in status_forcelist range and retries have been exhausted.
NB: raise_on_status is relatively new, and has not made it into a release of urllib3 or requests yet. The raise_on_status keyword argument appears to have made it into the standard library at most in python version 3.6.
To make requests retry on specific HTTP status codes, use status_forcelist. For example, status_forcelist=[503] will retry on status code 503 (service unavailable).
By default, the retry only fires for these conditions:
- Could not get a connection from the pool.
TimeoutErrorHTTPExceptionraised (from http.client in Python 3 else httplib). This seems to be low-level HTTP exceptions, like URL or protocol not formed correctly.SocketErrorProtocolError
Notice that these are all exceptions that prevent a regular HTTP response from being received. If any regular response is generated, no retry is done. Without using the status_forcelist, even a response with status 500 will not be retried.
To make it behave in a manner which is more intuitive for working with a remote API or web server, I would use the above code snippet, which forces retries on statuses 500, 502, 503 and 504, all of which are not uncommon on the web and (possibly) recoverable given a big enough backoff period.
EDITED: Import Retry class directly from urllib3.
How to set URL query params in Vue with Vue-Router
Actually you can just push query like this: this.$router.push({query: {plan: 'private'}})
manage.py runserver
For people who are using CentOS7, In order to allow access to port 8000, you need to modify firewall rules in a new SSH connection:
sudo firewall-cmd --zone=public --permanent --add-port=8000/tcp
sudo firewall-cmd --reload
Get root password for Google Cloud Engine VM
I had the same problem. Even after updating the password using sudo passwd it was not working. I had to give "multiple" roles for my user through IAM & Admin Refer Screen Shot on IAM & Admin screen of google cloud
After that i restarted the VM. Then again changed the password and then it worked.
user1@sap-hanaexpress-public-1-vm:~> sudo passwd
New password:
Retype new password:
passwd: password updated successfully
user1@sap-hanaexpress-public-1-vm:~> su
Password:
sap-hanaexpress-public-1-vm:/home/user1 # whoami
root
sap-hanaexpress-public-1-vm:/home/user1 #
How to get the azure account tenant Id?
For AAD-B2C it is fairly simple. From Azure Portal with a B2C directory associated, go to your B2C directory (I added the "Azure AD B2C" to my portal's left menu). In the B2C directory click on "User flows (policies) directory menu item. In the policies pane click on one of your policies you previously added to select it. It should open a pane for the policy. Click "Properties". In the next pane is a section, "Token compatibility settings" which has a property "Issuer". Your AAD-B2C tenant GUID is contained in the URL.
How to put sshpass command inside a bash script?
Try the "-o StrictHostKeyChecking=no" option to ssh("-o" being the flag that tells ssh that your are going to use an option). This accepts any incoming RSA key from your ssh connection, even if the key is not in the "known host" list.
sshpass -p 'password' ssh -o StrictHostKeyChecking=no user@host 'command'
What does the [Flags] Enum Attribute mean in C#?
Apologies if someone already noticed this scenario. A perfect example of flags we can see in reflection. Yes Binding Flags ENUM.
[System.Flags]
[System.Runtime.InteropServices.ComVisible(true)]
[System.Serializable]
public enum BindingFlags
Usage
// BindingFlags.InvokeMethod
// Call a static method.
Type t = typeof (TestClass);
Console.WriteLine();
Console.WriteLine("Invoking a static method.");
Console.WriteLine("-------------------------");
t.InvokeMember ("SayHello", BindingFlags.InvokeMethod | BindingFlags.Public |
BindingFlags.Static, null, null, new object [] {});
Check variable equality against a list of values
If you have access to Underscore, you can use the following:
if (_.contains([1, 3, 12], foo)) {
// ...
}
contains used to work in Lodash as well (prior to V4), now you have to use includes
if (_.includes([1, 3, 12], foo)) {
handleYellowFruit();
}
Is calling destructor manually always a sign of bad design?
What about this?
Destructor is not called if an exception is thrown from the constructor, so I have to call it manually to destroy handles that have been created in the constructor before the exception.
class MyClass {
HANDLE h1,h2;
public:
MyClass() {
// handles have to be created first
h1=SomeAPIToCreateA();
h2=SomeAPIToCreateB();
try {
...
if(error) {
throw MyException();
}
}
catch(...) {
this->~MyClass();
throw;
}
}
~MyClass() {
SomeAPIToDestroyA(h1);
SomeAPIToDestroyB(h2);
}
};
Export html table data to Excel using JavaScript / JQuery is not working properly in chrome browser
Excel export script works on IE7+, Firefox and Chrome.
function fnExcelReport()
{
var tab_text="<table border='2px'><tr bgcolor='#87AFC6'>";
var textRange; var j=0;
tab = document.getElementById('headerTable'); // id of table
for(j = 0 ; j < tab.rows.length ; j++)
{
tab_text=tab_text+tab.rows[j].innerHTML+"</tr>";
//tab_text=tab_text+"</tr>";
}
tab_text=tab_text+"</table>";
tab_text= tab_text.replace(/<A[^>]*>|<\/A>/g, "");//remove if u want links in your table
tab_text= tab_text.replace(/<img[^>]*>/gi,""); // remove if u want images in your table
tab_text= tab_text.replace(/<input[^>]*>|<\/input>/gi, ""); // reomves input params
var ua = window.navigator.userAgent;
var msie = ua.indexOf("MSIE ");
if (msie > 0 || !!navigator.userAgent.match(/Trident.*rv\:11\./)) // If Internet Explorer
{
txtArea1.document.open("txt/html","replace");
txtArea1.document.write(tab_text);
txtArea1.document.close();
txtArea1.focus();
sa=txtArea1.document.execCommand("SaveAs",true,"Say Thanks to Sumit.xls");
}
else //other browser not tested on IE 11
sa = window.open('data:application/vnd.ms-excel,' + encodeURIComponent(tab_text));
return (sa);
}
Just create a blank iframe:
<iframe id="txtArea1" style="display:none"></iframe>
Call this function on:
<button id="btnExport" onclick="fnExcelReport();"> EXPORT </button>
Export MySQL data to Excel in PHP
PHPExcel is your friend. Very easy to use and works like a charm.
MySQL Alter Table Add Field Before or After a field already present
$query = "ALTER TABLE `" . $table_prefix . "posts_to_bookmark`
ADD COLUMN `ping_status` INT(1) NOT NULL
AFTER `<TABLE COLUMN BEFORE THIS COLUMN>`";
I believe you need to have ADD COLUMN and use AFTER, not BEFORE.
In case you want to place column at the beginning of a table, use the FIRST statement:
$query = "ALTER TABLE `" . $table_prefix . "posts_to_bookmark`
ADD COLUMN `ping_status` INT(1) NOT NULL
FIRST";
Python list subtraction operation
If the lists allow duplicate elements, you can use Counter from collections:
from collections import Counter
result = list((Counter(x)-Counter(y)).elements())
If you need to preserve the order of elements from x:
result = [ v for c in [Counter(y)] for v in x if not c[v] or c.subtract([v]) ]
Free Barcode API for .NET
Could the Barcode Rendering Framework at Codeplex GitHub be of help?
jquery find element by specific class when element has multiple classes
you are looking for http://api.jquery.com/hasClass/
<div id="mydiv" class="foo bar"></div>
$('#mydiv').hasClass('foo') //returns ture
Parse RSS with jQuery
UPDATE [4/25/2016] Now better written and fully supported version with more options and abilities hosted at GitHub.jQRSS
I saw the Selected Answer by Nathan Strutz, however, the jQuery Plugin page link is still down and the home page for that site did not seem to load. I tried a few other solutions and found most of them to be, not only out-dated, but EASY! Thus I threw my hat out there and made my own plugin, and with the dead links here, this seems like a great place to submit an answer. If you're looking for this answer in 2012 (soon to b 2013) you may notice the frustration of dead links and old advice here as I did. Below is a link to my modern plugin example as well as the code to the plugin! Simply copy the code into a JS file & link it in your header like any other plugin. Use is EXTREMELY EZ!
Plugin Code
2/9/2015 - made long overdue update to check forconsolebefore sending commands to it! Should help with older IE issues.
(function($) {
if (!$.jQRSS) {
$.extend({
jQRSS: function(rss, options, func) {
if (arguments.length <= 0) return false;
var str, obj, fun;
for (i=0;i<arguments.length;i++) {
switch(typeof arguments[i]) {
case "string":
str = arguments[i];
break;
case "object":
obj = arguments[i];
break;
case "function":
fun = arguments[i];
break;
}
}
if (str == null || str == "") {
if (!obj['rss']) return false;
if (obj.rss == null || obj.rss == "") return false;
}
var o = $.extend(true, {}, $.jQRSS.defaults);
if (typeof obj == "object") {
if ($.jQRSS.methods.getObjLength(obj) > 0) {
o = $.extend(true, o, obj);
}
}
if (str != "" && !o.rss) o.rss = str;
o.rss = escape(o.rss);
var gURL = $.jQRSS.props.gURL
+ $.jQRSS.props.type
+ "?v=" + $.jQRSS.props.ver
+ "&q=" + o.rss
+ "&callback=" + $.jQRSS.props.callback;
var ajaxData = {
num: o.count,
output: o.output,
};
if (o.historical) ajaxData.scoring = $.jQRSS.props.scoring;
if (o.userip != null) ajaxData.scoring = o.userip;
$.ajax({
url: gURL,
beforeSend: function (jqXHR, settings) { if (window['console']) { console.log(new Array(30).join('-'), "REQUESTING RSS XML", new Array(30).join('-')); console.log({ ajaxData: ajaxData, ajaxRequest: settings.url, jqXHR: jqXHR, settings: settings, options: o }); console.log(new Array(80).join('-')); } },
dataType: o.output != "xml" ? "json" : "xml",
data: ajaxData,
type: "GET",
xhrFields: { withCredentials: true },
error: function (jqXHR, textStatus, errorThrown) { return new Array("ERROR", { jqXHR: jqXHR, textStatus: textStatus, errorThrown: errorThrown } ); },
success: function (data, textStatus, jqXHR) {
var f = data['responseData'] ? data.responseData['feed'] ? data.responseData.feed : null : null,
e = data['responseData'] ? data.responseData['feed'] ? data.responseData.feed['entries'] ? data.responseData.feed.entries : null : null : null
if (window['console']) {
console.log(new Array(30).join('-'), "SUCCESS", new Array(30).join('-'));
console.log({ data: data, textStatus: textStatus, jqXHR: jqXHR, feed: f, entries: e });
console.log(new Array(70).join('-'));
}
if (fun) {
return fun.call(this, data['responseData'] ? data.responseData['feed'] ? data.responseData.feed : data.responseData : null);
}
else {
return { data: data, textStatus: textStatus, jqXHR: jqXHR, feed: f, entries: e };
}
}
});
}
});
$.jQRSS.props = {
callback: "?",
gURL: "http://ajax.googleapis.com/ajax/services/feed/",
scoring: "h",
type: "load",
ver: "1.0"
};
$.jQRSS.methods = {
getObjLength: function(obj) {
if (typeof obj != "object") return -1;
var objLength = 0;
$.each(obj, function(k, v) { objLength++; })
return objLength;
}
};
$.jQRSS.defaults = {
count: "10", // max 100, -1 defaults 100
historical: false,
output: "json", // json, json_xml, xml
rss: null, // url OR search term like "Official Google Blog"
userip: null
};
}
})(jQuery);
USE
// Param ORDER does not matter, however, you must have a link and a callback function
// link can be passed as "rss" in options
// $.jQRSS(linkORsearchString, callbackFunction, { options })
$.jQRSS('someUrl.xml', function(feed) { /* do work */ })
$.jQRSS(function(feed) { /* do work */ }, 'someUrl.xml', { count: 20 })
$.jQRSS('someUrl.xml', function(feed) { /* do work */ }, { count: 20 })
$.jQRSS({ count: 20, rss: 'someLink.xml' }, function(feed) { /* do work */ })
$.jQRSS('Search Words Here instead of a Link', function(feed) { /* do work */ })
// TODO: Needs fixing
Options
{
count: // default is 10; max is 100. Setting to -1 defaults to 100
historical: // default is false; a value of true instructs the system to return any additional historical entries that it might have in its cache.
output: // default is "json"; "json_xml" retuns json object with xmlString / "xml" returns the XML as String
rss: // simply an alternate place to put news feed link or search terms
userip: // as this uses Google API, I'll simply insert there comment on this:
/* Reference: https://developers.google.com/feed/v1/jsondevguide
This argument supplies the IP address of the end-user on
whose behalf the request is being made. Google is less
likely to mistake requests for abuse when they include
userip. In choosing to utilize this parameter, please be
sure that you're in compliance with any local laws,
including any laws relating to disclosure of personal
information being sent.
*/
}
Add error bars to show standard deviation on a plot in R
In addition to @csgillespie's answer, segments is also vectorised to help with this sort of thing:
plot (x, y, ylim=c(0,6))
segments(x,y-sd,x,y+sd)
epsilon <- 0.02
segments(x-epsilon,y-sd,x+epsilon,y-sd)
segments(x-epsilon,y+sd,x+epsilon,y+sd)
Calling a method inside another method in same class
It is just an overload. The add method is from the ArrayList class. Look that Staff inherits from it.
UIBarButtonItem in navigation bar programmatically?
Just setup UIBarButtonItem with customView
For example:
var leftNavBarButton = UIBarButtonItem(customView:yourButton)
self.navigationItem.leftBarButtonItem = leftNavBarButton
or use setFunction:
self.navigationItem.setLeftBarButtonItem(UIBarButtonItem(customView: yourButton), animated: true);
Access host database from a docker container
If you want access to a Docker container where there is a DB, you have to add a bash:
docker exec -it postgresql bash
postgresql is the container name.
Once inside, from the bash, access to DB e.g:
$psql -U postgres
Is gcc's __attribute__((packed)) / #pragma pack unsafe?
As ams said above, don't take a pointer to a member of a struct that's packed. This is simply playing with fire. When you say __attribute__((__packed__)) or #pragma pack(1), what you're really saying is "Hey gcc, I really know what I'm doing." When it turns out that you do not, you can't rightly blame the compiler.
Perhaps we can blame the compiler for it's complacency though. While gcc does have a -Wcast-align option, it isn't enabled by default nor with -Wall or -Wextra. This is apparently due to gcc developers considering this type of code to be a brain-dead "abomination" unworthy of addressing -- understandable disdain, but it doesn't help when an inexperienced programmer bumbles into it.
Consider the following:
struct __attribute__((__packed__)) my_struct {
char c;
int i;
};
struct my_struct a = {'a', 123};
struct my_struct *b = &a;
int c = a.i;
int d = b->i;
int *e __attribute__((aligned(1))) = &a.i;
int *f = &a.i;
Here, the type of a is a packed struct (as defined above). Similarly, b is a pointer to a packed struct. The type of of the expression a.i is (basically) an int l-value with 1 byte alignment. c and d are both normal ints. When reading a.i, the compiler generates code for unaligned access. When you read b->i, b's type still knows it's packed, so no problem their either. e is a pointer to a one-byte-aligned int, so the compiler knows how to dereference that correctly as well. But when you make the assignment f = &a.i, you are storing the value of an unaligned int pointer in an aligned int pointer variable -- that's where you went wrong. And I agree, gcc should have this warning enabled by default (not even in -Wall or -Wextra).
How can I tell which button was clicked in a PHP form submit?
In HTML:
<input type="submit" id="btnSubmit" name="btnSubmit" value="Save Changes" />
<input type="submit" id="btnDelete" name="btnDelete" value="Delete" />
In PHP:
if (isset($_POST["btnSubmit"])){
// "Save Changes" clicked
} else if (isset($_POST["btnDelete"])){
// "Delete" clicked
}
Splitting String with delimiter
You can also do:
Integer a = '1182-2'.split('-')[0] as Integer
Integer b = '1182-2'.split('-')[1] as Integer
//a=1182 b=2
E: gnupg, gnupg2 and gnupg1 do not seem to be installed, but one of them is required for this operation
Just install the updated versions of all of them.
apt-get install -y gnupg2 gnupg gnupg1
Get HTML5 localStorage keys
for (var key in localStorage){
console.log(key)
}
EDIT: this answer is getting a lot of upvotes, so I guess it's a common question. I feel like I owe it to anyone who might stumble on my answer and think that it's "right" just because it was accepted to make an update. Truth is, the example above isn't really the right way to do this. The best and safest way is to do it like this:
for ( var i = 0, len = localStorage.length; i < len; ++i ) {
console.log( localStorage.getItem( localStorage.key( i ) ) );
}
How to style the menu items on an Android action bar
Chris answer is working for me...
My values-v11/styles.xml file:
<resources>
<style name="LightThemeSelector" parent="android:Theme.Holo.Light.DarkActionBar">
<item name="android:actionBarStyle">@style/ActionBar</item>
<item name="android:editTextBackground">@drawable/edit_text_holo_light</item>
<item name="android:actionMenuTextAppearance">@style/MyActionBar.MenuTextStyle</item>
</style>
<!--sets the point size to the menu item(s) in the upper right of action bar-->
<style name="MyActionBar.MenuTextStyle" parent="android:style/TextAppearance.Holo.Widget.ActionBar.Title">
<item name="android:textSize">25sp</item>
</style>
<!-- sets the background of the actionbar to a PNG file in my drawable folder.
displayOptions unset allow me to NOT SHOW the application icon and application name in the upper left of the action bar-->
<style name="ActionBar" parent="@android:style/Widget.Holo.ActionBar">
<item name="android:background">@drawable/actionbar_background</item>
<item name="android:displayOptions"></item>
</style>
<style name="inputfield" parent="android:Theme.Holo.Light">
<item name="android:textColor">@color/red2</item>
</style>
</resources>
Why check both isset() and !empty()
"Empty": only works on variables. Empty can mean different things for different variable types (check manual: http://php.net/manual/en/function.empty.php).
"isset": checks if the variable exists and checks for a true NULL or false value. Can be unset by calling "unset". Once again, check the manual.
Use of either one depends of the variable type you are using.
I would say, it's safer to check for both, because you are checking first of all if the variable exists, and if it isn't really NULL or empty.
Convert objective-c typedef to its string equivalent
I like the #define way of doing this:
// Place this in your .h file, outside the @interface block
typedef enum {
JPG,
PNG,
GIF,
PVR
} kImageType;
#define kImageTypeArray @"JPEG", @"PNG", @"GIF", @"PowerVR", nil
// Place this in the .m file, inside the @implementation block
// A method to convert an enum to string
-(NSString*) imageTypeEnumToString:(kImageType)enumVal
{
NSArray *imageTypeArray = [[NSArray alloc] initWithObjects:kImageTypeArray];
return [imageTypeArray objectAtIndex:enumVal];
}
source (source no longer available)
Issue with background color in JavaFX 8
Both these work for me. Maybe post a complete example?
import javafx.application.Application;
import javafx.beans.binding.Bindings;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.ToggleButton;
import javafx.scene.layout.Background;
import javafx.scene.layout.BackgroundFill;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.CornerRadii;
import javafx.scene.layout.HBox;
import javafx.scene.layout.VBox;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
public class PaneBackgroundTest extends Application {
@Override
public void start(Stage primaryStage) {
BorderPane root = new BorderPane();
VBox vbox = new VBox();
root.setCenter(vbox);
ToggleButton toggle = new ToggleButton("Toggle color");
HBox controls = new HBox(5, toggle);
controls.setAlignment(Pos.CENTER);
root.setBottom(controls);
// vbox.styleProperty().bind(Bindings.when(toggle.selectedProperty())
// .then("-fx-background-color: cornflowerblue;")
// .otherwise("-fx-background-color: white;"));
vbox.backgroundProperty().bind(Bindings.when(toggle.selectedProperty())
.then(new Background(new BackgroundFill(Color.CORNFLOWERBLUE, CornerRadii.EMPTY, Insets.EMPTY)))
.otherwise(new Background(new BackgroundFill(Color.WHITE, CornerRadii.EMPTY, Insets.EMPTY))));
Scene scene = new Scene(root, 300, 250);
primaryStage.setTitle("Hello World!");
primaryStage.setScene(scene);
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}
How to scroll to specific item using jQuery?
You can scroll by jQuery and JavaScript Just need two element jQuery and this JavaScript code :
$(function() {
// Generic selector to be used anywhere
$(".js-scroll-to-id").click(function(e) {
// Get the href dynamically
var destination = $(this).attr('href');
// Prevent href=“#” link from changing the URL hash (optional)
e.preventDefault();
// Animate scroll to destination
$('html, body').animate({
scrollTop: $(destination).offset().top
}, 1500);
});
});
$(function() {_x000D_
// Generic selector to be used anywhere_x000D_
$(".js-scroll-to-id").click(function(e) {_x000D_
_x000D_
// Get the href dynamically_x000D_
var destination = $(this).attr('href');_x000D_
_x000D_
// Prevent href=“#” link from changing the URL hash (optional)_x000D_
e.preventDefault();_x000D_
_x000D_
// Animate scroll to destination_x000D_
$('html, body').animate({_x000D_
scrollTop: $(destination).offset().top_x000D_
}, 1500);_x000D_
});_x000D_
});#pane1 {_x000D_
background: #000;_x000D_
width: 400px;_x000D_
height: 400px;_x000D_
}_x000D_
_x000D_
#pane2 {_x000D_
background: #ff0000;_x000D_
width: 400px;_x000D_
height: 400px;_x000D_
}_x000D_
_x000D_
#pane3 {_x000D_
background: #ccc;_x000D_
width: 400px;_x000D_
height: 400px;_x000D_
}<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>_x000D_
<ul class="nav">_x000D_
<li>_x000D_
<a href="#pane1" class=" js-scroll-to-id">Item 1</a>_x000D_
</li>_x000D_
<li>_x000D_
<a href="#pane2" class="js-scroll-to-id">Item 2</a>_x000D_
</li>_x000D_
<li>_x000D_
<a href="#pane3" class=" js-scroll-to-id">Item 3</a>_x000D_
</li>_x000D_
</ul>_x000D_
<div id="pane1"></div>_x000D_
<div id="pane2"></div>_x000D_
<div id="pane3"></div>_x000D_
<!-- example of a fixed nav menu -->_x000D_
<ul class="nav">_x000D_
<li>_x000D_
<a href="#pane3" class="js-scroll-to-id">Item 1</a>_x000D_
</li>_x000D_
<li>_x000D_
<a href="#pane2" class="js-scroll-to-id">Item 2</a>_x000D_
</li>_x000D_
<li>_x000D_
<a href="#pane1" class="js-scroll-to-id">Item 3</a>_x000D_
</li>_x000D_
</ul>Using HttpClient and HttpPost in Android with post parameters
I've just checked and i have the same code as you and it works perferctly. The only difference is how i fill my List for the params :
I use a : ArrayList<BasicNameValuePair> params
and fill it this way :
params.add(new BasicNameValuePair("apikey", apikey);
I do not use any JSONObject to send params to the webservices.
Are you obliged to use the JSONObject ?
How to convert integer to decimal in SQL Server query?
select cast (height as decimal)/10 as HeightDecimal
Scrolling a div with jQuery
There's a plug-in for this if you don't want to write a bare-bones implementation yourself. It's called "scrollTo" (link). It allows you to perform programmed scrolling to certain points, or use values like -= 10px for continuous scrolling.
what does -zxvf mean in tar -zxvf <filename>?
Instead of wading through the description of all the options, you can jump to 3.4.3 Short Options Cross Reference under the info tar command.
x means --extract. v means --verbose. f means --file. z means --gzip. You can combine one-letter arguments together, and f takes an argument, the filename. There is something you have to watch out for:
Short options' letters may be clumped together, but you are not required to do this (as compared to old options; see below). When short options are clumped as a set, use one (single) dash for them all, e.g., ''tar' -cvf'. Only the last option in such a set is allowed to have an argument(1).
This old way of writing 'tar' options can surprise even experienced users. For example, the two commands:tar cfz archive.tar.gz file tar -cfz archive.tar.gz fileare quite different. The first example uses 'archive.tar.gz' as the value for option 'f' and recognizes the option 'z'. The second example, however, uses 'z' as the value for option 'f' -- probably not what was intended.
Convert .cer certificate to .jks
keytool comes with the JDK installation (in the bin folder):
keytool -importcert -file "your.cer" -keystore your.jks -alias "<anything>"
This will create a new keystore and add just your certificate to it.
So, you can't convert a certificate to a keystore: you add a certificate to a keystore.
How do I plot list of tuples in Python?
With gnuplot using gplot.py
from gplot import *
l = [(0, 6.0705199999997801e-08), (1, 2.1015700100300739e-08),
(2, 7.6280656623374823e-09), (3, 5.7348209304555086e-09),
(4, 3.6812203579604238e-09), (5, 4.1572516753310418e-09)]
gplot.log('y')
gplot(*zip(*l))
NUnit Unit tests not showing in Test Explorer with Test Adapter installed
One other cause to this problem is if you open a project from a mapped drive - Visual Studio handles such projects properly, but apparently Nunit doesn't support them.
Copying the project to a physical fixed the issue.
Connect to SQL Server 2012 Database with C# (Visual Studio 2012)
I tested all the answers here, but for me, none worked. So I studied a bit the problem, and finally I found the connection string needed. To get this string, you do:
1. in you project name:
a. right click the project name,
b. click Add,
c. select SQL Server Database (obviously you can rename it as you wish).
Now the new desired database will be added to your project.
2. The database is visible in the Server Explorer window.
3. Left click the database name in the Server Explorer window; now check the Solution Explorer window, and you will find the "Connection String", along side with Provider, State, Type, Version.
4. Copy the connection string provided, and put it in the Page_Load method:
string source = @"Data Source=(LocalDB)\v11.0;AttachDbFilename=c:\x\x\documents\visual studio 2013\Projects\WebApplication3\WebApplication3\App_Data\Product.mdf;Integrated Security=True";
SqlConnection conn = new SqlConnection(source);
conn.Open();
//your code here;
conn.Close();
I renamed my database as Product. Also, in the "AttachDbFilename", you must replace "c:\x\x\documents\" with your path to the phisical address of the .mdf file.
It worked for me, but I must mention this method works for VS2012 and VS2013. Don't know about other versions.
Convert list of ASCII codes to string (byte array) in Python
I much prefer the array module to the struct module for this kind of tasks (ones involving sequences of homogeneous values):
>>> import array
>>> array.array('B', [17, 24, 121, 1, 12, 222, 34, 76]).tostring()
'\x11\x18y\x01\x0c\xde"L'
no len call, no string manipulation needed, etc -- fast, simple, direct, why prefer any other approach?!
Correct MySQL configuration for Ruby on Rails Database.yml file
If you have multiple databases for testing and development this might help
development:
adapter: mysql2
encoding: utf8
reconnect: false
database: DBNAME
pool: 5
username: usr
password: paswd
shost: localhost
test:
adapter: mysql2
encoding: utf8
reconnect: false
database: DBNAME
pool: 5
username: usr
password: paswd
shost: localhost
production:
adapter: mysql2
encoding: utf8
reconnect: false
database: DBNAME
pool: 5
username: usr
password: paswd
shost: localhost
Generate HTML table from 2D JavaScript array
I know this is an old question, but for those perusing the web like me, here's another solution:
Use replace() on the commas and create a set of characters to determine the end of a row. I just add -- to end of the internal arrays. That way you don't have to run a for function.
Here's a JSFiddle: https://jsfiddle.net/0rpb22pt/2/
First, you have to get a table inside your HTML and give it an id:
<table id="thisTable"><tr><td>Click me</td></tr></table>
Here's your array edited for this method:
thisArray=[["row 1, cell 1__", "row 2, cell 2--"], ["row 2, cell 1__", "row 2, cell 2"]];
Notice the added -- at the end of each array.
Because you also have commas inside of arrays, you have to differentiate them somehow so you don't end up messing up your table- adding __ after cells (besides the last one in a row) works. If you didn't have commas in your cell, this step wouldn't be necessary though.
Now here's your function:
function tryit(){
document
.getElementById("thisTable")
.innerHTML="<tr><td>"+String(thisArray)
.replace(/--,/g,"</td></tr><tr><td>")
.replace(/__,/g,"</td><td>");
}
It works like this:
- Call your table and get to setting the
innerHTML.document.getElementById("thisTable").innerHTML - Start by adding HTML tags to start a row and data.
"<tr><td>" - Add
thisArrayas aString().+String(thisArray) - Replace every
--that ends up before a new row with the closing and opening of data and row..replace(/--,/g,"</td></tr><tr><td>") - Other commas signify separate data within rows. So replace all commas the closing and opening of data. In this case not all commas are between rows because the cells have commas, so we had to differentiate those with
__:.replace(/__,/g,"</td><td>"). Normally you'd just do.replace(/,/g,"</td><td>").
As long as you don't mind adding some stray characters into your array, it takes up a lot less code and is simple to implement.
IntelliJ and Tomcat.. Howto..?
Please verify that the required plug-ins are enabled in Settings | Plugins, most likely you've disabled several of them, that's why you don't see all the facet options.
For the step by step tutorial, see: Creating a simple Web application and deploying it to Tomcat.
How to check version of python modules?
I suggest opening a python shell in terminal (in the python version you are interested), importing the library, and getting its __version__ attribute.
>>> import statlib
>>> statlib.__version__
>>> import construct
>>> contruct.__version__
Note 1: We must regard the python version. If we have installed different versions of python, we have to open the terminal in the python version we are interested in. For example, opening the terminal with python3.8 can (surely will) give a different version of a library than opening with python3.5 or python2.7.
Note 2: We avoid using the print function, because its behavior depends on python2 or python3. We do not need it, the terminal will show the value of the expression.
Can't specify the 'async' modifier on the 'Main' method of a console app
class Program
{
public static EventHandler AsyncHandler;
static void Main(string[] args)
{
AsyncHandler+= async (sender, eventArgs) => { await AsyncMain(); };
AsyncHandler?.Invoke(null, null);
}
private async Task AsyncMain()
{
//Your Async Code
}
}
Converting a String to Object
String extends Object, which means an Object. Object o = a; If you really want to get as Object, you may do like below.
String s = "Hi";
Object a =s;
How to escape single quotes in MySQL
You should escape the special characters using the \ character.
This is Ashok's Pen.
Becomes:
This is Ashok\'s Pen.
How to program a delay in Swift 3
Try the following function implemented in Swift 3.0 and above
func delayWithSeconds(_ seconds: Double, completion: @escaping () -> ()) {
DispatchQueue.main.asyncAfter(deadline: .now() + seconds) {
completion()
}
}
Usage
delayWithSeconds(1) {
//Do something
}
Change column type in pandas
pandas >= 1.0
Here's a chart that summarises some of the most important conversions in pandas.
Conversions to string are trivial .astype(str) and are not shown in the figure.
"Hard" versus "Soft" conversions
Note that "conversions" in this context could either refer to converting text data into their actual data type (hard conversion), or inferring more appropriate data types for data in object columns (soft conversion). To illustrate the difference, take a look at
df = pd.DataFrame({'a': ['1', '2', '3'], 'b': [4, 5, 6]}, dtype=object)
df.dtypes
a object
b object
dtype: object
# Actually converts string to numeric - hard conversion
df.apply(pd.to_numeric).dtypes
a int64
b int64
dtype: object
# Infers better data types for object data - soft conversion
df.infer_objects().dtypes
a object # no change
b int64
dtype: object
# Same as infer_objects, but converts to equivalent ExtensionType
df.convert_dtypes().dtypes
jQuery: How to get to a particular child of a parent?
If I understood your problem correctly, $(this).parents('.box').children('.something1') Is this what you are looking for?
Javascript String to int conversion
This is to do with JavaScript's + in operator - if a number and a string are "added" up, the number is converted into a string:
0 + 1; //1
'0' + 1; // '01'
To solve this, use the + unary operator, or use parseInt():
+'0' + 1; // 1
parseInt('0', 10) + 1; // 1
The unary + operator converts it into a number (however if it's a decimal it will retain the decimal places), and parseInt() is self-explanatory (converts into number, ignoring decimal places).
The second argument is necessary for parseInt() to use the correct base when leading 0s are placed:
parseInt('010'); // 8 in older browsers, 10 in newer browsers
parseInt('010', 10); // always 10 no matter what
There's also parseFloat() if you need to convert decimals in strings to their numeric value - + can do that too but it behaves slightly differently: that's another story though.
Laravel Eloquent groupBy() AND also return count of each group
Here is a more Laravel way to handle group by without the need to use raw statements.
$sources = $sources->where('age','>', 31)->groupBy('age');
$output = null;
foreach($sources as $key => $source) {
foreach($source as $item) {
//get each item in the group
}
$output[$key] = $source->count();
}
What are the lengths of Location Coordinates, latitude and longitude?
I am aware there are already several answers, but I added this, as this adds substantial information about the decimal places and hence the asked maximum length.
The length of latitude and langitude depend on precision. The absolute maximum length for each is:
- Latitude: 12 characters (example: -90.00000001)
- Longitude: 13 characters (example: -180.00000001)
For both holds: a maximum of 8 decial places is possible (though not commonly used).
Explanation for the dependency on precision:
See the full table at Decimal degrees article on Wikipedia
Basic example of using .ajax() with JSONP?
There is even easier way how to work with JSONP using jQuery
$.getJSON("http://example.com/something.json?callback=?", function(result){
//response data are now in the result variable
alert(result);
});
The ? on the end of the URL tells jQuery that it is a JSONP request instead of JSON. jQuery registers and calls the callback function automatically.
For more detail refer to the jQuery.getJSON documentation.
Video auto play is not working in Safari and Chrome desktop browser
Chrome does not allow to auto play video with sound on, so make sure to add muted attribute to the video tag like this
<video width="320" height="240" autoplay muted>
<source src="video.mp4" type="video/mp4">
</video>
TypeError: can only concatenate list (not "str") to list
I think what you want to do is add a new item to your list, so you have change the line newinv=inventory+str(add) with this one:
newinv = inventory.append(add)
What you are doing now is trying to concatenate a list with a string which is an invalid operation in Python.
However I think what you want is to add and delete items from a list, in that case your if/else block should be:
if selection=="use":
print(inventory)
remove=input("What do you want to use? ")
inventory.remove(remove)
print(inventory)
elif selection=="pickup":
print(inventory)
add=input("What do you want to pickup? ")
inventory.append(add)
print(inventory)
You don't need to build a new inventory list every time you add a new item.
My httpd.conf is empty
The /etc/apache2/httpd.conf is empty in Ubuntu, because the Apache configuration resides in /etc/apache2/apache2.conf!
“httpd.conf is for user options.” No it isn't, it's there for historic reasons.
Using Apache server, all user options should go into a new *.conf-file inside /etc/apache2/conf.d/. This method should be "update-safe", as httpd.conf or apache2.conf may get overwritten on the next server update.
Inside /etc/apache2/apache2.conf, you will find the following line, which includes those files:
# Include generic snippets of statements
Include conf.d/
As of Apache 2.4+ the user configuration directory is /etc/apache2/conf-available/. Use a2enconf FILENAME_WITHOUT_SUFFIX to enable the new configuration file or manually create a symlink in /etc/apache2/conf-enabled/. Be aware that as of Apache 2.4 the configuration files must have the suffix .conf (e.g. conf-available/my-settings.conf);
What is href="#" and why is it used?
Unfortunately, the most common use of <a href="#"> is by lazy programmers who want clickable non-hyperlink javascript-coded elements that behave like anchors, but they can't be arsed to add cursor: pointer; or :hover styles to a class for their non-hyperlink elements, and are additionally too lazy to set href to javascript:void(0);.
The problem with this is that one <a href="#" onclick="some_function();"> or another inevitably ends up with a javascript error, and an anchor with an onclick javascript error always ends up following its href. Normally this ends up being an annoying jump to the top of the page, but in the case of sites using <base>, <a href="#"> is handled as <a href="[base href]/#">, resulting in an unexpected navigation. If any logable errors are being generated, you won't see them in the latter case unless you enable persistent logs.
If an anchor element is used as a non-anchor it should have its href set to javascript:void(0); for the sake of graceful degradation.
I just wasted two days debugging a random unexpected page redirect that should have simply refreshed the page, and finally tracked it down to a function raising the click event of an <a href="#">. Replacing the # with javascript:void(0); fixed it.
The first thing I'm doing Monday is purging the project of all instances of <a href="#">.
Git Bash is extremely slow on Windows 7 x64
I've encountered the same problem running Git for Windows (msysgit) on Windows 7 x64 as a limited user account for quite some time.
From what I've read here and other places, the common theme seems to be the lack of administrative privileges and/or UAC. Since UAC is off on my system, the explanation that it is trying to write/delete something in the program files directory makes the most sense to me.
In any case, I've resolved my problem by installing the portable version of Git 1.8 with zipinstaller. Note that I had to unpack the .7z distribution file and repack it as a ZIP file in order for zipinstaller to work. I also had to manually add that directory to my system path.
The performance is fine now. Even though it is installed in the Program Files (x86) directory, which I don't have permissions for as a limited user, it doesn't seem to suffer from the same problem.
I ascribe this either to the fact that the portable version is a bit more conservative in where it writes/deletes files, which is probably the case, or to the upgrade from 1.7 to 1.8. I'm not going to try to pin down which one is the reason, suffice to say it works much better now, including Bash.
How to Truncate a string in PHP to the word closest to a certain number of characters?
I have a function that does almost what you want, if you'll do a few edits, it will fit exactly:
<?php
function stripByWords($string,$length,$delimiter = '<br>') {
$words_array = explode(" ",$string);
$strlen = 0;
$return = '';
foreach($words_array as $word) {
$strlen += mb_strlen($word,'utf8');
$return .= $word." ";
if($strlen >= $length) {
$strlen = 0;
$return .= $delimiter;
}
}
return $return;
}
?>
How to base64 encode image in linux bash / shell
Base 64 for html:
file="DSC_0251.JPG"
type=$(identify -format "%m" "$file" | tr '[A-Z]' '[a-z]')
echo "data:image/$type;base64,$(base64 -w 0 "$file")"
SQL RANK() over PARTITION on joined tables
SELECT a.C_ID,a.QRY_ID,a.RES_ID,b.SCORE,ROW_NUMBER() OVER (ORDER BY SCORE DESC) AS [RANK]
FROM CONTACTS a JOIN RSLTS b ON a.QRY_ID=b.QRY_ID AND a.RES_ID=b.RES_ID
ORDER BY a.C_ID
Map a network drive to be used by a service
You could us the 'net use' command:
var p = System.Diagnostics.Process.Start("net.exe", "use K: \\\\Server\\path");
var isCompleted = p.WaitForExit(5000);
If that does not work in a service, try the Winapi and PInvoke WNetAddConnection2
Edit: Obviously I misunderstood you - you can not change the sourcecode of the service, right? In that case I would follow the suggestion by mdb, but with a little twist: Create your own service (lets call it mapping service) that maps the drive and add this mapping service to the dependencies for the first (the actual working) service. That way the working service will not start before the mapping service has started (and mapped the drive).