Programs & Examples On #Linq to entities

This tag is for questions about LINQ to Entities, which means LINQ queries using the ADO.NET Entity Framework. Note that this is different than LINQ to SQL or other LINQ providers.

LINQ to Entities does not recognize the method

If anyone is looking for a VB.Net answer (as I was initially), here it is:

Public Function IsSatisfied() As Expression(Of Func(Of Charity, String, String, Boolean))

Return Function(charity, name, referenceNumber) (String.IsNullOrWhiteSpace(name) Or
                                                         charity.registeredName.ToLower().Contains(name.ToLower()) Or
                                                         charity.alias.ToLower().Contains(name.ToLower()) Or
                                                         charity.charityId.ToLower().Contains(name.ToLower())) And
                                                    (String.IsNullOrEmpty(referenceNumber) Or
End Function

How to add a default "Select" option to this ASP.NET DropDownList control?

The reason it is not working is because you are adding an item to the list and then overriding the whole list with a new DataSource which will clear and re-populate your list, losing the first manually added item.

So, you need to do this in reverse like this:

Status status = new Status();
DropDownList1.DataSource = status.getData();
DropDownList1.DataValueField = "ID";
DropDownList1.DataTextField = "Description";

// Then add your first item
DropDownList1.Items.Insert(0, "Select");

How do I get the max ID with Linq to Entity?

Do that like this

db.Users.OrderByDescending(u => u.UserId).FirstOrDefault();

Linq to Entities join vs groupjoin

Let's suppose you have two different classes:

public class Person
    public string Name, Email;
    public Person(string name, string email)
        Name = name;
        Email = email;
class Data
    public string Mail, SlackId;
    public Data(string mail, string slackId)
        Mail = mail;
        SlackId = slackId;

Now, let's Prepare data to work with:

var people = new Person[]
        new Person("Sudi", "[email protected]"),
        new Person("Simba", "[email protected]"),
        new Person("Sarah", string.Empty)
    var records = new Data[]
        new Data("[email protected]", "Sudi_Try"),
        new Data("[email protected]", "Sudi@Test"),
        new Data("[email protected]", "SimbaLion")

You will note that [email protected] has got two slackIds. I have made that for demonstrating how Join works.

Let's now construct the query to join Person with Data:

var query = people.Join(records,
        x => x.Email,
        y => y.Mail,
        (person, record) => new { Name = person.Name, SlackId = record.SlackId});

After constructing the query, you could also iterate over it with a foreach like so:

foreach (var item in query)
        Console.WriteLine($"{item.Name} has Slack ID {item.SlackId}");

Let's also output the result for GroupJoin:

            x => x.Email,
            y => y.Mail,
            (person, recs) => new {
                Name = person.Name,
                SlackIds = recs.Select(r => r.SlackId).ToArray() // You could materialize //whatever way you want.

You will notice that the GroupJoin will put all SlackIds in a single group.

How to store a list in a column of a database table

I think in certain cases, you can create a FAKE "list" of items in the database, for example, the merchandise has a few pictures to show its details, you can concatenate all the IDs of pictures split by comma and store the string into the DB, then you just need to parse the string when you need it. I am working on a website now and I am planning to use this way.

Best way to check if object exists in Entity Framework?

If you don't want to execute SQL directly, the best way is to use Any(). This is because Any() will return as soon as it finds a match. Another option is Count(), but this might need to check every row before returning.

Here's an example of how to use it:

if (context.MyEntity.Any(o => o.Id == idToMatch))
    // Match!

And in

If context.MyEntity.Any(function(o) o.Id = idToMatch) Then
    ' Match!
End If

How to do SQL Like % in Linq?

Well indexOf works for me too

var result = from c in SampleList
where c.LongName.IndexOf(SearchQuery) >= 0
select c;

How to get first record in each group using Linq

Use it to achieve what you want. Then decide which properties you want to return.

yourList.OrderBy(l => l.Id).GroupBy(l => new { GroupName = l.F1}).Select(r => r.Key.GroupName)

How to use DbContext.Database.SqlQuery<TElement>(sql, params) with stored procedure? EF Code First CTP5

You should supply the SqlParameter instances in the following way:

    "mySpName @param1, @param2, @param3",
    new SqlParameter("param1", param1),
    new SqlParameter("param2", param2),
    new SqlParameter("param3", param3)

Problem with converting int to string in Linq to entities

Can you try:

var items = from c in contacts
        select new ListItem
            Value = Convert.ToString(c.ContactId), 
            Text = c.Name

SQL to Entity Framework Count Group-By

Edit: EF Core 2.1 finally supports GroupBy

But always look out in the console / log for messages. If you see a notification that your query could not be converted to SQL and will be evaluated locally then you may need to rewrite it.

Entity Framework 7 (now renamed to Entity Framework Core 1.0 / 2.0) does not yet support GroupBy() for translation to GROUP BY in generated SQL (even in the final 1.0 release it won't). Any grouping logic will run on the client side, which could cause a lot of data to be loaded.

Eventually code written like this will automagically start using GROUP BY, but for now you need to be very cautious if loading your whole un-grouped dataset into memory will cause performance issues.

For scenarios where this is a deal-breaker you will have to write the SQL by hand and execute it through EF.

If in doubt fire up Sql Profiler and see what is generated - which you should probably be doing anyway.

Entity Framework VS LINQ to SQL VS ADO.NET with stored procedures?

LINQ-to-SQL is a remarkable piece of technology that is very simple to use, and by and large generates very good queries to the back end. LINQ-to-EF was slated to supplant it, but historically has been extremely clunky to use and generated far inferior SQL. I don't know the current state of affairs, but Microsoft promised to migrate all the goodness of L2S into L2EF, so maybe it's all better now.

Personally, I have a passionate dislike of ORM tools (see my diatribe here for the details), and so I see no reason to favour L2EF, since L2S gives me all I ever expect to need from a data access layer. In fact, I even think that L2S features such as hand-crafted mappings and inheritance modeling add completely unnecessary complexity. But that's just me. ;-)

LEFT JOIN in LINQ to entities?

You can use this not only in entities but also store procedure or other data source:

var customer = (from cus in _billingCommonservice.BillingUnit.CustomerRepository.GetAll()  
                          join man in _billingCommonservice.BillingUnit.FunctionRepository.ManagersCustomerValue()  
                          on cus.CustomerID equals man.CustomerID  
                          // start left join  
                          into a  
                          from b in a.DefaultIfEmpty(new DJBL_uspGetAllManagerCustomer_Result() )  
                          select new { cus.MobileNo1,b.ActiveStatus });  

The cast to value type 'Int32' failed because the materialized value is null

To allow a nullable Amount field, just use the null coalescing operator to convert nulls to 0.

var creditsSum = (from u in context.User
              join ch in context.CreditHistory on u.ID equals ch.UserID                                        
              where u.ID == userID
              select ch.Amount ?? 0).Sum();

Like Operator in Entity Framework?

I don't know anything about EF really, but in LINQ to SQL you usually express a LIKE clause using String.Contains:

where entity.Name.Contains("xyz")

translates to

WHERE Name LIKE '%xyz%'

(Use StartsWith and EndsWith for other behaviour.)

I'm not entirely sure whether that's helpful, because I don't understand what you mean when you say you're trying to implement LIKE. If I've misunderstood completely, let me know and I'll delete this answer :)

Linq to Entities - SQL "IN" clause

I also tried to work with an SQL-IN-like thing - querying against an Entity Data Model. My approach is a string builder to compose a big OR-expression. That's terribly ugly, but I'm afraid it's the only way to go right now.

Now well, that looks like this:

Queue<Guid> productIds = new Queue<Guid>(Products.Select(p => p.Key));
if(productIds.Count > 0)
    StringBuilder sb = new StringBuilder();
    sb.AppendFormat("{0}.ProductId = Guid\'{1}\'", entities.Products.Name, productIds.Dequeue());
    while(productIds.Count > 0)
        sb.AppendFormat(" OR {0}.ProductId = Guid\'{1}\'",
          entities.Products.Name, productIds.Dequeue());

Working with GUIDs in this context: As you can see above, there is always the word "GUID" before the GUID ifself in the query string fragments. If you don't add this, ObjectQuery<T>.Where throws the following exception:

The argument types 'Edm.Guid' and 'Edm.String' are incompatible for this operation., near equals expression, line 6, column 14.

Found this in MSDN Forums, might be helpful to have in mind.


... looking forward for the next version of .NET and Entity Framework, when everything get's better. :)

LINQ to Entities how to update a record

Just modify one of the returned entities:

Customer c = (from x in dataBase.Customers
             where x.Name == "Test"
             select x).First();
c.Name = "New Name";

Note, you can only update an entity (something that extends EntityObject, not something that you have projected using something like select new CustomObject{Name = x.Name}

Linq where clause compare only date value without time value

Simple workaround to this problem to compare date part only

var _My_ResetSet_Array = _DB
                    .Where(x => x.Active == true && 
                               x.DateTimeValueColumn.Year == DateTime.Now.Year
                            && x.DateTimeValueColumn.Month == DateTime.Now.Month
                            && x.DateTimeValueColumn.Day == DateTime.Now.Day);

Because 'Date' datatype is not supported by linq to entity , where as Year, Month and Day are 'int' datatypes and are supported.

Entity framework left join

For 2 and more left joins (left joining creatorUser and initiatorUser )

IQueryable<CreateRequestModel> queryResult = from r in authContext.Requests
                                             join candidateUser in authContext.AuthUsers
                                             on r.CandidateId equals candidateUser.Id
                                             join creatorUser in authContext.AuthUsers
                                             on r.CreatorId equals creatorUser.Id into gj
                                             from x in gj.DefaultIfEmpty()
                                             join initiatorUser in authContext.AuthUsers
                                             on r.InitiatorId equals initiatorUser.Id into init
                                             from x1 in init.DefaultIfEmpty()

                                             where candidateUser.UserName.Equals(candidateUsername)
                                             select new CreateRequestModel
                                                 UserName = candidateUser.UserName,
                                                 CreatorId = (x == null ? String.Empty : x.UserName),
                                                 InitiatorId = (x1 == null ? String.Empty : x1.UserName),
                                                 CandidateId = candidateUser.UserName

How to compare only date components from DateTime in EF?

Just always compare the Date property of DateTime, instead of the full date time.

When you make your LINQ query, use date.Date in the query, ie:

var results = from c in collection
              where c.Date == myDateTime.Date
              select c;

Cannot implicitly convert type 'System.Linq.IQueryable' to 'System.Collections.Generic.IList'

If using a where clause be sure to include .First() if you do not want a IQueryable object.

"NOT IN" clause in LINQ to Entities

I took a list and used,


Note: Make sure to use List and not Ilist

The specified type member 'Date' is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties

Another solution could be:

var eventsCustom = eventCustomRepository.FindAllEventsCustomByUniqueStudentReference(userDevice.UniqueStudentReference).AsEnumerable()
   .Where(x => x.DateTimeStart.Date == currentDate.Date).AsQueryable();

inner join in linq to entities

You can find a whole bunch of Linq examples in visual studio. Just select Help -> Samples, and then unzip the Linq samples.

Open the linq samples solution and open the LinqSamples.cs of the SampleQueries project.

The answer you are looking for is in method Linq14:

int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 };
int[] numbersB = { 1, 3, 5, 7, 8 };

var pairs =
   from a in numbersA
   from b in numbersB
   where a < b
   select new {a, b};

The specified type member is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported

Checking Count() before the WHERE clause solved my problem. It is cheaper than ToList()

if (authUserList != null && _list.Count() > 0)
    _list = _list.Where(l => authUserList.Contains(l.CreateUserId));

"A lambda expression with a statement body cannot be converted to an expression tree"

Use this overload of select:

Obj[] myArray = objects.Select(new Func<Obj,Obj>( o =>
    var someLocalVar = o.someVar;

    return new Obj() 
       Var1 = someLocalVar,
       Var2 = o.var2 

The type or namespace name 'Objects' does not exist in the namespace 'System.Data'

if you want to use "System.Data.Objects.EntityFunctions"

use "System.Data.Entity.DbFunctions" in EF 6.1+

How to monitor SQL Server table changes by using c#?

In the interests of completeness there are a couple of other solutions which (in my opinion) are more orthodox than solutions relying on the SqlDependency (and SqlTableDependency) classes. SqlDependency was originally designed to make refreshing distributed webserver caches easier, and so was built to a different set of requirements than if it were designed as an event producer.

There are broadly four options, some of which have not been covered here already:

  • Change Tracking
  • CDC
  • Triggers to queues
  • CLR

Change tracking


Change tracking is a lightweight notification mechanism in SQL server. Basically, a database-wide version number is incremented with every change to any data. The version number is then written to the change tracking tables with a bit mask including the names of the columns which were changed. Note, the actual change is not persisted. The notification only contains the information that a particular data entity has changed. Further, because the change table versioning is cumulative, change notifications on individual items are not preserved and are overwritten by newer notifications. This means that if an entity changes twice, change tracking will only know about the most recent change.

In order to capture these changes in c#, polling must be used. The change tracking tables can be polled and each change inspected to see if is of interest. If it is of interest, it is necessary to then go directly to the data to retrieve the current state.

Change Data Capture


Change data capture (CDC) is more powerful but most costly than change tracking. Change data capture will track and notify changes based on monitoring the database log. Because of this CDC has access to the actual data which has been changed, and keeps a record of all individual changes.

Similarly to change tracking, in order to capture these changes in c#, polling must be used. However, in the case of CDC, the polled information will contain the change details, so it's not strictly necessary to go back to the data itself.

Triggers to queues


This technique depends on triggers on the tables from which notifications are required. Each change will fire a trigger, and the trigger will write this information to a service broker queue. The queue can then be connected to via C# using the Service Broker Message Processor (sample in the link above).

Unlike change tracking or CDC, triggers to queues do not rely on polling and thereby provides realtime eventing.


This is a technique I have seen used, but I would not recommend it. Any solution which relies on the CLR to communicate externally is a hack at best. The CLR was designed to make writing complex data processing code easier by leveraging C#. It was not designed to wire in external dependencies like messaging libraries. Furthermore, CLR bound operations can break in clustered environments in unpredictable ways.

This said, it is fairly straightforward to set up, as all you need to do is register the messaging assembly with CLR and then you can call away using triggers or SQL jobs.

In summary...

It has always been a source of amazement to me that Microsoft has steadfastly refused to address this problem space. Eventing from database to code should be a built-in feature of the database product. Considering that Oracle Advanced Queuing combined with the MessageAvailable event provided reliable database eventing to C# more than 10 years ago, this is woeful from MS.

The upshot of this is that none of the solutions listed to this question are very nice. They all have technical drawbacks and have a significant setup cost. Microsoft if you're listening, please sort out this sorry state of affairs.

Easy pretty printing of floats in python?

print "[%s]"%", ".join(map(str,yourlist))

This will avoid the rounding errors in the binary representation when printed, without introducing a fixed precision constraint (like formating with "%.2f"):

[9.0, 0.053, 0.0325754, 0.0108928, 0.0557025, 0.0793303]

How to return a list of keys from a Hash Map?

Use the keySet() method to return a set with all the keys of a Map.

If you want to keep your Map ordered you can use a TreeMap.

How to get IntPtr from byte[] in C#

Here's a twist on @user65157's answer (+1 for that, BTW):

I created an IDisposable wrapper for the pinned object:

class AutoPinner : IDisposable
   GCHandle _pinnedArray;
   public AutoPinner(Object obj)
      _pinnedArray = GCHandle.Alloc(obj, GCHandleType.Pinned);
   public static implicit operator IntPtr(AutoPinner ap)
      return ap._pinnedArray.AddrOfPinnedObject(); 
   public void Dispose()

then use it like thusly:

using (AutoPinner ap = new AutoPinner(MyManagedObject))
   UnmanagedIntPtr = ap;  // Use the operator to retrieve the IntPtr
   //do your stuff

I found this to be a nice way of not forgetting to call Free() :)

Google Maps setCenter()

I searched and searched and finally found that ie needs to know the map size. Set the map size to match the div size.

map = new GMap2(document.getElementById("map_canvas2"), { size: new GSize(850, 600) });

<div id="map_canvas2" style="width: 850px; height: 600px">

git switch branch without discarding local changes

You could use --merge/-m git checkout option: git checkout -m <another-branch>

-m --merge

When switching branches, if you have local modifications to one or more files that are different between the current branch and the branch to which you are switching, the command refuses to switch branches in order to preserve your modifications in context. However, with this option, a three-way merge between the current branch, your working tree contents, and the new branch is done, and you will be on the new branch.


Sample settings.xml

A standard Maven settings.xml file is as follows:

<settings xmlns="" xmlns:xsi=""







To access a proxy, you can find detailed information on the official Maven page here:

Maven-Settings - Settings

I hope it helps for someone.

Update elements in a JSONObject

Generic way to update the any JSONObjet with new values.

private static void updateJsonValues(JsonObject jsonObj) {
    for (Map.Entry<String, JsonElement> entry : jsonObj.entrySet()) {
        JsonElement element = entry.getValue();
        if (element.isJsonArray()) {
        } else if (element.isJsonObject()) {
        } else if (element.isJsonPrimitive()) {
            jsonObj.addProperty(entry.getKey(), "<provide new value>");


private static void parseJsonArray(JsonArray asJsonArray) {
    for (int index = 0; index < asJsonArray.size(); index++) {
        JsonElement element = asJsonArray.get(index);
        if (element.isJsonArray()) {
        } else if (element.isJsonObject()) {


C++ pass an array by reference

Arrays can only be passed by reference, actually:

void foo(double (&bar)[10])

This prevents you from doing things like:

double arr[20];
foo(arr); // won't compile

To be able to pass an arbitrary size array to foo, make it a template and capture the size of the array at compile time:

template<typename T, size_t N>
void foo(T (&bar)[N])
    // use N here

You should seriously consider using std::vector, or if you have a compiler that supports c++11, std::array.

How do I use a regular expression to match any string, but at least 3 characters?

You could try with simple 3 dots. refer to the code in perl below

$a =~ m /.../ #where $a is your string

bad operand types for binary operator "&" java

Because & has a lesser priority than ==.

Your code is equivalent to a[0] & (1 == 0), and unless a[0] is a boolean this won't compile...

You need to:

(a[0] & 1) == 0

etc etc.

(yes, Java does hava a boolean & operator -- a non shortcut logical and)

Creating an array of objects in Java

For generic class it is necessary to create a wrapper class. For Example:

Set<String>[] sets = new HashSet<>[10]

results in: "Cannot create a generic array"

Use instead:

        class SetOfS{public Set<String> set = new HashSet<>();}
        SetOfS[] sets = new SetOfS[10];  

REST API Best practice: How to accept list of parameter values as input

You might want to check out RFC 6570. This URI Template spec shows many examples of how urls can contain parameters.

capture div into image using html2canvas

If you just want to have screenshot of a div, you can do it like this

html2canvas($('#div'), {
  onrendered: function(canvas) {
    var img = canvas.toDataURL();

Bootstrap 3: how to make head of dropdown link clickable in navbar

This enables the link in the top-level menu of the dropdown when it's opened and disables it when closed, with the only drawback of apparently having to "tap" twice outside of the dropdown to close it in mobile devices.

$(document).on("page:load", function(){
    $('body').on('', function (e) {
    $('body').on('', function (e) {

Note this assumes the "standard" markup and Turbolinks (Rails). You can try with $(document).ready(...)

SQL Query for Logins

Is this what you're after?

select * from master.syslogins

how to check if a datareader is null or empty

First of all, you probably want to check for a DBNull not a regular Null.

Or you could look at the IsDBNull method

How to use absolute path in twig functions

The following works for me:

<img src="{{ asset('bundle/myname/img/image.gif', null, true) }}" />

How to create an empty array in Swift?

Swift 5

// Create an empty array
var emptyArray = [String]()

// Add values to array by appending (Adds values as the last element)

// Add values to array by inserting (Adds to a specified position of the list)
emptyArray.insert("Samsung", at: 0)

// Remove elements from an array by index number
emptyArray.remove(at: 2)

// Remove elements by specifying the element
if let removeElement = emptyArray.firstIndex(of: "Samsung") {
    emptyArray.remove(at: removeElement)

A similar answer is given but that doesn't work for the latest version of Swift (Swift 5), so here is the updated answer. Hope it helps! :)

What is difference between Lightsail and EC2?

Lightsail VPSs are bundles of existing AWS products, offered through a significantly simplified interface. The difference is that Lightsail offers you a limited and fixed menu of options but with much greater ease of use. Other than the narrower scope of Lightsail in order to meet the requirements for simplicity and low cost, the underlying technology is the same.

The pre-defined bundles can be described:

% aws lightsail --region us-east-1 get-bundles
    "bundles": [
            "name": "Nano",
            "power": 300,
            "price": 5.0,
            "ramSizeInGb": 0.5,
            "diskSizeInGb": 20,
            "transferPerMonthInGb": 1000,
            "cpuCount": 1,
            "instanceType": "t2.nano",
            "isActive": true,
            "bundleId": "nano_1_0"

It's worth reading through the Amazon EC2 T2 Instances documentation, particularly the CPU Credits section which describes the base and burst performance characteristics of the underlying instances.

Importantly, since your Lightsail instances run in VPC, you still have access to the full spectrum of AWS services, e.g. S3, RDS, and so on, as you would from any EC2 instance.

Moving from JDK 1.7 to JDK 1.8 on Ubuntu

This is what I do on debian - I suspect it should work on ubuntu (amend the version as required + adapt the folder where you want to copy the JDK files as you wish, I'm using /opt/jdk):

wget --header "Cookie: oraclelicense=accept-securebackup-cookie"
sudo mkdir /opt/jdk
sudo tar -zxf jdk-8u71-linux-x64.tar.gz -C /opt/jdk/
rm jdk-8u71-linux-x64.tar.gz

Then update-alternatives:

sudo update-alternatives --install /usr/bin/java java /opt/jdk/jdk1.8.0_71/bin/java 1
sudo update-alternatives --install /usr/bin/javac javac /opt/jdk/jdk1.8.0_71/bin/javac 1

Select the number corresponding to the /opt/jdk/jdk1.8.0_71/bin/java when running the following commands:

sudo update-alternatives --config java
sudo update-alternatives --config javac

Finally, verify that the correct version is selected:

java -version
javac -version

How to change text and background color?

You can also use PDCurses library. (

How to increase Neo4j's maximum file open limit (ulimit) in Ubuntu?

You could alter the init script for neo4j to do a ulimit -n 40000 before running neo4j.

However, I can't help but feel you are barking up the wrong tree. Does neo4j legitimately need more than 10,000 open file descriptors? This sounds very much like a bug in neo4j or the way you are using it. I would try to address that.

Remove Identity from a column in a table

If you want to do this without adding and populating a new column, without reordering the columns, and with almost no downtime because no data is changing on the table, let's do some magic with partitioning functionality (but since no partitions are used you don't need Enterprise edition):

  1. Remove all foreign keys that point to this table
  2. Script the table to be created; rename everything e.g. 'MyTable2', 'MyIndex2', etc. Remove the IDENTITY specification.
  3. You should now have two "identical"-ish tables, one full, the other empty with no IDENTITY.
  4. Run ALTER TABLE [Original] SWITCH TO [Original2]
  5. Now your original table will be empty and the new one will have the data. You have switched the metadata for the two tables (instant).
  6. Drop the original (now-empty table), exec sys.sp_rename to rename the various schema objects back to the original names, and then you can recreate your foreign keys.

For example, given:

, Value NVARCHAR(300)
CREATE NONCLUSTERED INDEX IX_Original_Value ON Original (Value);

SELECT 'abcd'
SELECT 'defg';

You can do the following:

--create new table with no IDENTITY
, Value NVARCHAR(300)
CREATE NONCLUSTERED INDEX IX_Original_Value2 ON Original2 (Value);

--data before switch
SELECT 'Original', *
FROM Original
SELECT 'Original2', *
FROM Original2;

ALTER TABLE Original SWITCH TO Original2;

--data after switch
SELECT 'Original', *
FROM Original
SELECT 'Original2', *
FROM Original2;

--clean up 
EXEC sys.sp_rename 'Original2.IX_Original_Value2', 'IX_Original_Value', 'INDEX';
EXEC sys.sp_rename 'Original2', 'Original', 'OBJECT';

UPDATE Original
SET Id = Id + 1;

FROM Original;

Send parameter to Bootstrap modal window?

I found the solution at: Passing data to a bootstrap modal

So simply use:


with 'book-id' is a attribute of modal with pre-fix 'data-'

Best practice for using assert?

In IDE's such as PTVS, PyCharm, Wing assert isinstance() statements can be used to enable code completion for some unclear objects.

Show Image View from file path?

You may use this to access a specific folder and get particular image

 public void Retrieve(String path, String Name)
    File imageFile = new File(path+Name);


        Bitmap myBitmap = BitmapFactory.decodeFile(path+Name);
        myImage = (ImageView) findViewById(;
        Toast.makeText(SaveImage.this, myBitmap.toString(), Toast.LENGTH_LONG).show();


And then you can call it by

Toast.makeText(SaveImage.this, "Saved", Toast.LENGTH_LONG).show();

Enum to String C++

You could throw the enum value and string into an STL map. Then you could use it like so.

   return myStringMap[Enum::Apple];

Detect change to ngModel on a select tag (Angular 2)


Separate the event and property bindings:

<select [ngModel]="selectedItem" (ngModelChange)="onChange($event)">
onChange(newValue) {
    this.selectedItem = newValue;  // don't forget to update the model here
    // ... do other stuff here ...

You could also use

<select [(ngModel)]="selectedItem" (ngModelChange)="onChange($event)">

and then you wouldn't have to update the model in the event handler, but I believe this causes two events to fire, so it is probably less efficient.

Old answer, before they fixed a bug in beta.1:

Create a local template variable and attach a (change) event:

<select [(ngModel)]="selectedItem" #item (change)="onChange(item.value)">


See also How can I get new selection in "select" in Angular 2?

Remove or adapt border of frame of legend using matplotlib

When plotting a plot using matplotlib:

How to remove the box of the legend?


How to change the color of the border of the legend box?

leg = plt.legend()

How to remove only the border of the box of the legend?

leg = plt.legend()

Interface/enum listing standard mime-type constants

As pointed out by an answer above, you can use which has the required constants.

I also wanted to share a really cool and handy link which I found that gives a reference to all the Javax constants in one place -

Maven error: Could not find or load main class org.codehaus.plexus.classworlds.launcher.Launcher

For other people who might run into this, don't forget to check ~/.mavenrc for M2_HOME or JAVA_HOME settings.

error LNK2019: unresolved external symbol _WinMain@16 referenced in function ___tmainCRTStartup

I'm not sure where to post this answer of mine but I think it's the right place. I came across this very error today and switching the subsystems didn't change a thing.

Changing the 64bit lib files to 32bit (x86) did the trick for me, I hope it will help someone out there !

How to update parent's state in React?

I like the answer regarding passing functions around, its a very handy technique.

On the flip side you can also achieve this using pub/sub or using a variant, a dispatcher, as Flux does. The theory is super simple, have component 5 dispatch a message which component 3 is listening for. Component 3 then updates its state which triggers the re-render. This requires stateful components, which, depending on your viewpoint, may or may not be an anti-pattern. I'm against them personally and would rather that something else is listening for dispatches and changes state from the very top-down (Redux does this, but adds additional terminology).

import { Dispatcher } from flux
import { Component } from React

const dispatcher = new Dispatcher()

// Component 3
// Some methods, such as constructor, omitted for brevity
class StatefulParent extends Component {
  state = {
    text: 'foo'

  componentDidMount() {
    dispatcher.register( dispatch => {
      if ( dispatch.type === 'change' ) {
        this.setState({ text: 'bar' })

  render() {
    return <h1>{ this.state.text }</h1>

// Click handler
const onClick = event => {
    type: 'change'

// Component 5 in your example
const StatelessChild = props => {
  return <button onClick={ onClick }>Click me</button> 

The dispatcher bundles with Flux is very simple, it simply registers callbacks and invokes them when any dispatch occurs, passing through the contents on the dispatch (in the above terse example there is no payload with the dispatch, simply a message id). You could adapt this to traditional pub/sub (e.g. using the EventEmitter from events, or some other version) very easily if that makes more sense to you.

docker error - 'name is already in use by container'

You have 2 options to fix this...

  1. Remove previous container using that name, with the command docker rm $(docker ps -aq --filter name=myContainerName)


  2. Rename current container to a different name i.e change this portion --name registry-v1 to something like --name myAnotherContainerName

You are getting this error because that container name ( i.e registry-v1) was used by another container in the past...even though that container may have exited i.e (currently not in use).

How to set -source 1.7 in Android Studio and Gradle

At current, Android doesn't support Java 7, only Java 6. New features in Java 7 such as the diamond syntax are therefore not currently supported. Finding sources to support this isn't easy, but I could find that the Dalvic engine is built upon a subset of Apache Harmony which only ever supported Java up to version 6. And if you check the system requirements for developing Android apps it also states that at least JDK 6 is needed (though this of course isn't real proof, just an indication). And this says pretty much the same as I have. If I find anything more substancial, I'll add it.

Edit: It seems Java 7 support has been added since I originally wrote this answer; check the answer by Sergii Pechenizkyi.

How to resize an image to a specific size in OpenCV?

Make a useful function like this:

IplImage* img_resize(IplImage* src_img, int new_width,int new_height)
    IplImage* des_img;
    return des_img;

Jenkins Slave port number for firewall

A slave isn't a server, it's a client type application. Network clients (almost) never use a specific port. Instead, they ask the OS for a random free port. This works much better since you usually run clients on many machines where the current configuration isn't known in advance. This prevents thousands of "client wouldn't start because port is already in use" bug reports every day.

You need to tell the security department that the slave isn't a server but a client which connects to the server and you absolutely need to have a rule which says client:ANY -> server:FIXED. The client port number should be >= 1024 (ports 1 to 1023 need special permissions) but I'm not sure if you actually gain anything by adding a rule for this - if an attacker can open privileged ports, they basically already own the machine.

If they argue, then ask them why they don't require the same rule for all the web browsers which people use in your company.

Loading context in Spring using web.xml

You can also load the context while defining the servlet itself (WebApplicationContext)


rather than (ApplicationContext)



or can do both together.

Drawback of just using WebApplicationContext is that it will load context only for this particular Spring entry point (DispatcherServlet) where as with above mentioned methods context will be loaded for multiple entry points (Eg. Webservice Servlet, REST servlet etc)

Context loaded by ContextLoaderListener will infact be a parent context to that loaded specifically for DisplacherServlet . So basically you can load all your business service, data access or repository beans in application context and separate out your controller, view resolver beans to WebApplicationContext.

Sending XML data using HTTP POST with PHP

you can use cURL library for posting data:

$ch = curl_init();
curl_setopt($ch, CURLOPT_HEADER, 0);
curl_setopt($ch, CURLOPT_RETURNTRANSFER,1);
curl_setopt($ch, CURLOPT_URL, "http://websiteURL");
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, "XML=".$xmlcontent."&password=".$password."&etc=etc");

where postfield contains XML you need to send - you will need to name the postfield the API service (Clickatell I guess) expects

Get an object attribute

To access field or method of an object use dot .:

user = User()
print user.fullName

If a name of the field will be defined at run time, use buildin getattr function:

field_name = "fullName"
print getattr(user, field_name) # prints content of user.fullName


I think that parse_str is what you're looking for, something like this should do the trick for you:

parse_str($_SERVER['QUERY_STRING'], $vars);

Then the $vars array will hold all the passed arguments.

Ways to iterate over a list in Java

For a backward search you should use the following:

for (ListIterator<SomeClass> iterator = list.listIterator(list.size()); iterator.hasPrevious();) {
    SomeClass item = iterator.previous();
    item.remove(); // For instance.

If you want to know a position, use iterator.previousIndex(). It also helps to write an inner loop that compares two positions in the list (iterators are not equal).

Node.JS: Getting error : [nodemon] Internal watch failed: watch ENOSPC

It appears that my max ports weren't configured correctly. I ran the following code and it worked...

echo fs.inotify.max_user_watches=582222 | sudo tee -a /etc/sysctl.conf && sudo sysctl -p

What this command does is to increase the number of watches allowed for a single user. By the default the number can be low (8192 for example). When nodemon tries to watch large numbers of directories for changes it has to create several watches, which can surpass that limit.

You could also solve this problem by:

sudo sysctl fs.inotify.max_user_watches=582222 && sudo sysctl -p

But the way it was written first will make this change permanent.

Python - round up to the nearest ten

This will round down correctly as well:

>>> n = 46
>>> rem = n % 10
>>> if rem < 5:
...     n = int(n / 10) * 10
... else:
...     n = int((n + 10) / 10) * 10
>>> 50

How to include external Python code to use in other files?

I've found the python inspect module to be very useful

For example with

import inspect

def dostuff():
    return __name__

DOSTUFF_SOURCE = inspect.getsource(dostuff)

if __name__ == "__main__":


And from the another script or the python console

import teststuff



And now dostuff should be in the local scope and dostuff() will return the console or scripts _name_ whereas executing test.dostuff() will return the python modules name.

Callback when CSS3 transition finishes

For transitions you can use the following to detect the end of a transition via jQuery:

$("#someSelector").bind("transitionend webkitTransitionEnd oTransitionEnd MSTransitionEnd", function(){ ... });

Mozilla has an excellent reference:

For animations it's very similar:

$("#someSelector").bind("animationend webkitAnimationEnd oAnimationEnd MSAnimationEnd", function(){ ... });

Note that you can pass all of the browser prefixed event strings into the bind() method simultaneously to support the event firing on all browsers that support it.


Per the comment left by Duck: you use jQuery's .one() method to ensure the handler only fires once. For example:

$("#someSelector").one("transitionend webkitTransitionEnd oTransitionEnd MSTransitionEnd", function(){ ... });

$("#someSelector").one("animationend webkitAnimationEnd oAnimationEnd MSAnimationEnd", function(){ ... });

Update 2:

jQuery bind() method has been deprecated, and on() method is preferred as of jQuery 1.7. bind()

You can also use off() method on the callback function to ensure it will be fired only once. Here is an example which is equivalent to using one() method:

.on("animationend webkitAnimationEnd oAnimationEnd MSAnimationEnd",
    // do something here


TypeError: Cannot read property 'then' of undefined

You need to return your promise to the calling function.

    var cUid=sessionService.get('uid');
    alert("in loginServce, cuid is "+cUid);
    var $checkSessionServer=$'data/check_session.php?cUid='+cUid);
        alert("session check returned!");
        console.log("checkSessionServer is "+$checkSessionServer);
    return $checkSessionServer; // <-- return your promise to the calling function

Logical operator in a handlebars.js {{#if}} conditional

taking this one up a notch, for those of you who live on the edge.

gist: Demo: Code snippet below

Handlebars Helper: {{#xif EXPRESSION}} {{else}} {{/xif}}

a helper to execute an IF statement with any expression

  1. EXPRESSION is a properly escaped String
  2. Yes you NEED to properly escape the string literals or just alternate single and double quotes
  3. you can access any global function or property i.e. encodeURIComponent(property)
  4. this example assumes you passed this context to your handlebars template( {name: 'Sam', age: '20' } ), notice age is a string, just for so I can demo parseInt() later in this post


 {{#xif " name == 'Sam' && age === '12' " }}



JavaScript: (it depends on another helper- keep reading)

 Handlebars.registerHelper("xif", function (expression, options) {
    return Handlebars.helpers["x"].apply(this, [expression, options]) ? options.fn(this) : options.inverse(this);

Handlebars Helper: {{x EXPRESSION}}

A helper to execute javascript expressions

  1. EXPRESSION is a properly escaped String
  2. Yes you NEED to properly escape the string literals or just alternate single and double quotes
  3. you can access any global function or property i.e. parseInt(property)
  4. this example assumes you passed this context to your handlebars template( {name: 'Sam', age: '20' } ), age is a string for demo purpose, it can be anything..


<p>Url: {{x "'hi' + name + ', ' + window.location.href + ' <---- this is your href,' + ' your Age is:' + parseInt(this.age, 10)"}}</p>


<p>Url: hi Sam, <---- this is your href, your Age is: 20</p>


This looks a little large because I expanded syntax and commented over almost each line for clarity purposes

Handlebars.registerHelper("x", function(expression, options) {_x000D_
  var result;_x000D_
  // you can change the context, or merge it with, options.hash_x000D_
  var context = this;_x000D_
  // yup, i use 'with' here to expose the context's properties as block variables_x000D_
  // you don't need to do {{x 'this.age + 2'}}_x000D_
  // but you can also do {{x 'age + 2'}}_x000D_
  // HOWEVER including an UNINITIALIZED var in a expression will return undefined as the result._x000D_
  with(context) {_x000D_
    result = (function() {_x000D_
      try {_x000D_
        return eval(expression);_x000D_
      } catch (e) {_x000D_
        console.warn('•Expression: {{x \'' + expression + '\'}}\n•JS-Error: ', e, '\n•Context: ', context);_x000D_
    }).call(context); // to make eval's lexical this=context_x000D_
  return result;_x000D_
Handlebars.registerHelper("xif", function(expression, options) {_x000D_
  return Handlebars.helpers["x"].apply(this, [expression, options]) ? options.fn(this) : options.inverse(this);_x000D_
var data = [{_x000D_
  firstName: 'Joan',_x000D_
  age: '21',_x000D_
  email: '[email protected]'_x000D_
}, {_x000D_
  firstName: 'Sam',_x000D_
  age: '18',_x000D_
  email: '[email protected]'_x000D_
}, {_x000D_
  firstName: 'Perter',_x000D_
  lastName: 'Smith',_x000D_
  age: '25',_x000D_
  email: '[email protected]'_x000D_
var source = $("#template").html();_x000D_
var template = Handlebars.compile(source);_x000D_
h1 {_x000D_
  font-size: large;_x000D_
.content {_x000D_
  padding: 10px;_x000D_
.person {_x000D_
  padding: 5px;_x000D_
  margin: 5px;_x000D_
  border: 1px solid grey;_x000D_
<script src=""></script>_x000D_
<script src=""></script>_x000D_
<script id="template" type="text/x-handlebars-template">_x000D_
  <div class="content">_x000D_
    {{#each this}}_x000D_
    <div class="person">_x000D_
      <h1>{{x  "'Hi ' + firstName"}}, {{x 'lastName'}}</h1>_x000D_
      <div>{{x '"you were born in " + ((new Date()).getFullYear() - parseInt(this.age, 10)) '}}</div>_x000D_
      {{#xif 'parseInt(age) >= 21'}} login here:_x000D_
      <a href="{{x 'encodeURIComponent(email)'}}">_x000D_{{x 'encodeURIComponent(email)'}}_x000D_
      {{else}} Please go back when you grow up. {{/xif}}_x000D_
<div id="main"></div>


if you want access upper level scope, this one is slightly different, the expression is the JOIN of all arguments, usage: say context data looks like this:

// data
{name: 'Sam', age: '20', address: { city: 'yomomaz' } }

// in template
// notice how the expression wrap all the string with quotes, and even the variables
// as they will become strings by the time they hit the helper
// play with it, you will immediately see the errored expressions and figure it out

{{#with address}}
    {{z '"hi " + "' ../ '" + " you live with " + "' city '"' }}


Handlebars.registerHelper("z", function () {
    var options = arguments[arguments.length - 1]
    delete arguments[arguments.length - 1];
    return Handlebars.helpers["x"].apply(this, [, 0).join(''), options]);

Handlebars.registerHelper("zif", function () {
    var options = arguments[arguments.length - 1]
    delete arguments[arguments.length - 1];
    return Handlebars.helpers["x"].apply(this, [, 0).join(''), options]) ? options.fn(this) : options.inverse(this);

python list in sql query as parameter

This Will Work If Number of Values in List equals to 1 or greater than 1

t = str(tuple(l))
if t[-2] == ',':
   t= t.replace(t[-2],"")
query = "select name from studens where id IN {}".format(t)

kill a process in bash

To interrupt it, you can try pressing ctrl c to send a SIGINT. If it doesn't stop it, you may try to kill it using kill -9 <pid>, which sends a SIGKILL. The latter can't be ignored/intercepted by the process itself (the one being killed).

To move the active process to background, you can press ctrl z. The process is sent to background and you get back to the shell prompt. Use the fg command to do the opposite.

Simplest way to download and unzip files in Node.js cross-platform?

Node has builtin support for gzip and deflate via the zlib module:

var zlib = require('zlib');

zlib.gunzip(gzipBuffer, function(err, result) {
    if(err) return console.error(err);


Edit: You can even pipe the data directly through e.g. Gunzip (using request):

var request = require('request'),
    zlib = require('zlib'),
    fs = require('fs'),
    out = fs.createWriteStream('out');

// Fetch, gunzip it and store the results in 'out'

For tar archives, there is Isaacs' tar module, which is used by npm.

Edit 2: Updated answer as zlib doesn't support the zip format. This will only work for gzip.

ssh remote host identification has changed

Edit /home/hostname /.ssh/known_hosts,and delete the 4 lines, and save it.

Then run ssh root@pong again, you will see message like this:Are you sure you want to continue connecting (yes/no)? yes, just print yes.

Note: If you got some problem, read the hints first, it will help.

Image UriSource and Data Binding

You can also simply set the Source attribute rather than using the child elements. To do this your class needs to return the image as a Bitmap Image. Here is an example of one way I've done it

<Image Width="90" Height="90" 
       Source="{Binding Path=ImageSource}"
       Margin="0,0,0,5" />

And the class property is simply this

public object ImageSource {
    get {
        BitmapImage image = new BitmapImage();

        try {
            image.CacheOption = BitmapCacheOption.OnLoad;
            image.CreateOptions = BitmapCreateOptions.IgnoreImageCache;
            image.UriSource = new Uri( FullPath, UriKind.Absolute );
            return DependencyProperty.UnsetValue;

        return image;

I suppose it may be a little more work than the value converter, but it is another option.

How to convert string to IP address and vice versa

here's easy-to-use, thread-safe c++ functions to convert uint32_t native-endian to string, and string to native-endian uint32_t:

#include <arpa/inet.h> // inet_ntop & inet_pton
#include <string.h> // strerror_r
#include <arpa/inet.h> // ntohl & htonl
using namespace std; // im lazy

string ipv4_int_to_string(uint32_t in, bool *const success = nullptr)
    string ret(INET_ADDRSTRLEN, '\0');
    in = htonl(in);
    const bool _success = (NULL != inet_ntop(AF_INET, &in, &ret[0], ret.size()));
    if (success)
        *success = _success;
    if (_success)
        ret.pop_back(); // remove null-terminator required by inet_ntop
    else if (!success)
        char buf[200] = {0};
        strerror_r(errno, buf, sizeof(buf));
        throw std::runtime_error(string("error converting ipv4 int to string ") + to_string(errno) + string(": ") + string(buf));
    return ret;
// return is native-endian
// when an error occurs: if success ptr is given, it's set to false, otherwise a std::runtime_error is thrown.
uint32_t ipv4_string_to_int(const string &in, bool *const success = nullptr)
    uint32_t ret;
    const bool _success = (1 == inet_pton(AF_INET, in.c_str(), &ret));
    ret = ntohl(ret);
    if (success)
        *success = _success;
    else if (!_success)
        char buf[200] = {0};
        strerror_r(errno, buf, sizeof(buf));
        throw std::runtime_error(string("error converting ipv4 string to int ") + to_string(errno) + string(": ") + string(buf));
    return ret;

fair warning, as of writing, they're un-tested. but these functions are exactly what i was looking for when i came to this thread.

How do I check whether a file exists without exceptions?

It isn't needed probably but if it is, here's some code

import os

def file_exists(path, filename):
    for file_or_folder in os.listdir(path):
        if file_or_folder == filename:
            return True
    return False

Pass correct "this" context to setTimeout callback?

EDIT: In summary, back in 2010 when this question was asked the most common way to solve this problem was to save a reference to the context where the setTimeout function call is made, because setTimeout executes the function with this pointing to the global object:

var that = this;
if (this.options.destroyOnHide) {
     setTimeout(function(){ that.tip.destroy() }, 1000);

In the ES5 spec, just released a year before that time, it introduced the bind method, this wasn't suggested in the original answer because it wasn't yet widely supported and you needed polyfills to use it but now it's everywhere:

if (this.options.destroyOnHide) {
     setTimeout(function(){ this.tip.destroy() }.bind(this), 1000);

The bind function creates a new function with the this value pre-filled.

Now in modern JS, this is exactly the problem arrow functions solve in ES6:

if (this.options.destroyOnHide) {
     setTimeout(() => { this.tip.destroy() }, 1000);

Arrow functions do not have a this value of its own, when you access it, you are accessing the this value of the enclosing lexical scope.

HTML5 also standardized timers back in 2011, and you can pass now arguments to the callback function:

if (this.options.destroyOnHide) {
     setTimeout(function(that){ that.tip.destroy() }, 1000, this);

See also:

How to write and save html file in python?

You can do it using write() :

#open file with *.html* extension to write html
file= open("my.html","w")
#write then close file

How to make a deep copy of Java ArrayList

public class Person{

    String s;
    Date d;

    public Person clone(){
        Person p = new Person();
        p.s = this.s.clone();
        p.d = this.d.clone();
        return p;

In your executing code:

ArrayList<Person> clone = new ArrayList<Person>();
for(Person p : originalList)

Xcode is not currently available from the Software Update server

I got the same issue on MacOS Catalina.

I think I identified the root cause: I have switched the default Apple ID account and the new one was not activated as a Developer account. When I ran the xcode-select --install command, I got the same error as stated in the issue description.

After reading this post on stackoverflow, I went on and I was asked to accept Developers terms. I think it enabled my account as a developer one. Then, I tried to run xcode-select --install again and it worked.

How to get client's IP address using JavaScript?

All the above answers have a server part, not pure client part. This should be provided by the web browser. At present, no web browser support this.

However, with this addon for firefox: You will have to ask your users to install this addon. (it's good from me, a 3rd party).

you can test whether the user has installed it.

var installed=window.IP!==undefined;

you can get it with javascript, if it is installed, then var ip=IP.getClient(); var IPclient=ip.IP; //while ip.url is the url

var IPserver=ip.IP;
var portServer=ip.port;
//while ip.url is the url

//or you can use IP.getBoth();

more information here:

Is it possible to iterate through JSONArray?

You can use the opt(int) method and use a classical for loop.

How to create a byte array in C++?

Byte is not a standard type in C/C++, so it is represented by char.

An advantage of this is that you can treat a basic_string as a byte array allowing for safe storage and function passing. This will help you avoid the memory leaks and segmentation faults you might encounter when using the various forms of char[] and char*.

For example, this creates a string as a byte array of null values:

typedef basic_string<unsigned char> u_string;

u_string bytes = u_string(16,'\0');

This allows for standard bitwise operations with other char values, including those stored in other string variables. For example, to XOR the char values of another u_string across bytes:

u_string otherBytes = "some more chars, which are just bytes";
for(int i = 0; i < otherBytes.length(); i++)
    bytes[i%16] ^= (int)otherBytes[i];

Converting std::__cxx11::string to std::string

In my case, I was having a similar problem:

/usr/bin/ld: Bank.cpp:(.text+0x19c): undefined reference to 'Account::SetBank(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)' collect2: error: ld returned 1 exit status

After some researches, I realized that the problem was being generated by the way that Visual Studio Code was compiling the Bank.cpp file. So, to solve that, I just prompted the follow command in order to compile the c++ file sucessful:

g++ Bank.cpp Account.cpp -o Bank

With the command above, It was able to linkage correctly the Header, Implementations and Main c++ files.

OBS: My g++ version: 9.3.0 on Ubuntu 20.04

How do I change the title of the "back" button on a Navigation Bar

Here's another way to do it.

In your parent view controller, implement the following method:

- (void) setBackBarButtonItemTitle:(NSString *)newTitle {
  self.navigationItem.backBarButtonItem.title = newTitle;

In your child view controller, when you want to change the title, this will work:

NSArray *viewControllerArray = [self.navigationController viewControllers];
int parentViewControllerIndex = [viewControllerArray count] - 2;
[[viewControllerArray objectAtIndex:parentViewControllerIndex] setBackBarButtonItemTitle:@"New Title"];

I was never able to get the parentViewController property to work:

[(ParentViewController *)(self.navigationController.parentViewController) setBackBarButtonItemTitle:@"New Title"];

I don't know if that's a bug or I'm not using it properly. But grabbing the second-to-last view controller in the viewControllers array points to the parent view controller, and I can call parent methods correctly with that reference.

window.onload vs <body onload=""/>

window.onload - Called after all DOM, JS files, Images, Iframes, Extensions and others completely loaded. This is equal to $(window).load(function() {});

body onload="" - Called once DOM loaded. This is equal to $(document).ready(function() {});

MetadataException: Unable to load the specified metadata resource

Another cause for this exception is when you include a related table in an ObjectQuery, but type in the wrong navigation property name.


var query = (from x in myDbObjectContext.Table1.Include("FKTableSpelledWrong") select x);

How do I refresh a DIV content?

This one $("#yourDiv").load(" #yourDiv > *"); is the best if you are planning to just reload a <div>

Make sure to use an id and not a class. Also, remember to paste <script src=""></script> in the <head> section of the html file, if you haven't already. In opposite case it won't work.

Regular expression to match a dot

"In the default mode, Dot (.) matches any character except a newline. If the DOTALL flag has been specified, this matches any character including a newline." (python Doc)

So, if you want to evaluate dot literaly, I think you should put it in square brackets:

>>> p = re.compile(r'\b(\w+[.]\w+)')
>>> resp ="blah blah blah [email protected] blah blah")

Ascending and Descending Number Order in java

int arr[] = { 12, 13, 54, 16, 25, 8, 78 };

for (int i = 0; i < arr.length; i++) {

How to workaround 'FB is not defined'?

It's pretty strange for FB not to be loaded in your javascript if you have the script tag there correctly. Check that you don't have any javascript blockers, ad blockers, tracking blockers etc installed in your browser that are neutralizing your FB Connect code.

How to create a .gitignore file

I want my contribution as well. This time, animated one :)

VIM (mini tutorial):

i   - start editing
ESC - get back to normal mode
:w  - save 
:q  - quit

enter image description here

use mysql SUM() in a WHERE clause

In general, a condition in the WHERE clause of an SQL query can reference only a single row. The context of a WHERE clause is evaluated before any order has been defined by an ORDER BY clause, and there is no implicit order to an RDBMS table.

You can use a derived table to join each row to the group of rows with a lesser id value, and produce the sum of each sum group. Then test where the sum meets your criterion.


INSERT INTO MyTable (id, cash) VALUES
  (1, 200), (2, 301), (3, 101), (4, 700);

  SELECT, SUM( AS cash_sum
  FROM MyTable t JOIN MyTable prev ON ( >
WHERE s.cash_sum >= 500


| id | cash_sum |
|  3 |      501 |

Recursively list all files in a directory including files in symlink directories

I knew tree was an appropriate, but I didn't have tree installed. So, I got a pretty close alternate here

find ./ | sed -e 's/[^-][^\/]*\//--/g;s/--/ |-/'

How do I cancel an HTTP fetch() request?

Let's polyfill:

  class AbortController {
    constructor() {
      this.aborted = false;
      this.signal = this.signal.bind(this);
    signal(abortFn, scope) {
      if (this.aborted) {
        abortFn.apply(scope, { name: 'AbortError' });
        this.aborted = false;
      } else {
        this.abortFn = abortFn.bind(scope);
    abort() {
      if (this.abortFn) {
        this.abortFn({ reason: 'canceled' });
        this.aborted = false;
      } else {
        this.aborted = true;

  const originalFetch = window.fetch;

  const customFetch = (url, options) => {
    const { signal } = options || {};

    return new Promise((resolve, reject) => {
      if (signal) {
        signal(reject, this);
      originalFetch(url, options)

  window.fetch = customFetch;

Please have in mind that the code is not tested! Let me know if you have tested it and something didn't work. It may give you warnings that you try to overwrite the 'fetch' function from the JavaScript official library.

How to resize Image in Android?

bm = Bitmap.createScaledBitmap(bitmapSource, width, height, true);


nginx error connect to php5-fpm.sock failed (13: Permission denied)

If you have declarations

pid = /run/


listen = /run/

in different configuration files, then root will owner of this file.

How can I shrink the drawable on a button?

You can use different sized drawables that are used with different screen densities/sizes, etc. so that your image looks right on all devices.

See here:

Plot 3D data in R

Not sure why the code above did not work for the library rgl, but the following link has a great example with the same library. Run the code in R and you will obtain a beautiful 3d plot that you can turn around in all angles.

## another example of 3d plot from my personal reserach, use rgl library
# 3D visualization device system


peak.height <- volcano;
ppm.index <- (1:nrow(volcano));
sample.index <- (1:ncol(volcano));

zlim <- range(peak.height)
zlen <- zlim[2] - zlim[1] + 1
colorlut <- terrain.colors(zlen) # height color lookup table
col <- colorlut[(peak.height-zlim[1]+1)] # assign colors to heights for each point

ppm.index1 <- ppm.index*zlim[2]/max(ppm.index);
sample.index1 <- sample.index*zlim[2]/max(sample.index) <- paste("plot3d ", "volcano", sep = "");
surface3d(ppm.index1, sample.index1, peak.height, color=col, back="lines", main =;
grid3d(c("x", "y+", "z"), n =20) <- paste("col.", 1:ncol(volcano), sep="");
sample.label <- as.integer(seq(1, length(, length = 5));

axis3d('y+',at = sample.index1[sample.label],[sample.label], cex = 0.3);
axis3d('y',at = sample.index1[sample.label],[sample.label], cex = 0.3)
axis3d('z',pos=c(0, 0, NA))

ppm.label <- as.integer(seq(1, length(ppm.index), length = 10));
axes3d('x', at=c(ppm.index1[ppm.label], 0, 0), abs(round(ppm.index[ppm.label], 2)), cex = 0.3);

title3d(main =, sub = "test", xlab = "ppm", ylab = "samples", zlab = "peak")

multiprocessing: How do I share a dict among multiple processes?

I'd like to share my own work that is faster than Manager's dict and is simpler and more stable than pyshmht library that uses tons of memory and doesn't work for Mac OS. Though my dict only works for plain strings and is immutable currently. I use linear probing implementation and store keys and values pairs in a separate memory block after the table.

from mmap import mmap
import struct
from timeit import default_timer
from multiprocessing import Manager
from pyshmht import HashTable

class shared_immutable_dict:
    def __init__(self, a):
        self.hs = 1 << (len(a) * 3).bit_length()
        kvp = self.hs * 4
        ht = [0xffffffff] * self.hs
        kvl = []
        for k, v in a.iteritems():
            h = self.hash(k)
            while ht[h] != 0xffffffff:
                h = (h + 1) & (self.hs - 1)
            ht[h] = kvp
            kvp += self.kvlen(k) + self.kvlen(v)

        self.m = mmap(-1, kvp)
        for p in ht:
        for x in kvl:
            if len(x) <= 0x7f:
                self.m.write(uint_format.pack(0x80000000 + len(x)))

    def hash(self, k):
        h = hash(k)
        h = (h + (h >> 3) + (h >> 13) + (h >> 23)) * 1749375391 & (self.hs - 1)
        return h

    def get(self, k, d=None):
        h = self.hash(k)
        while True:
            x = uint_format.unpack(self.m[h * 4:h * 4 + 4])[0]
            if x == 0xffffffff:
                return d
            if k == self.read_kv():
                return self.read_kv()
            h = (h + 1) & (self.hs - 1)

    def read_kv(self):
        sz = ord(self.m.read_byte())
        if sz & 0x80:
            sz = uint_format.unpack(chr(sz) +[0] - 0x80000000

    def kvlen(self, k):
        return len(k) + (1 if len(k) <= 0x7f else 4)

    def __contains__(self, k):
        return self.get(k, None) is not None

    def close(self):

uint_format = struct.Struct('>I')

def uget(a, k, d=None):
    return to_unicode(a.get(to_str(k), d))

def uin(a, k):
    return to_str(k) in a

def to_unicode(s):
    return s.decode('utf-8') if isinstance(s, str) else s

def to_str(s):
    return s.encode('utf-8') if isinstance(s, unicode) else s

def mmap_test():
    n = 1000000
    d = shared_immutable_dict({str(i * 2): '1' for i in xrange(n)})
    start_time = default_timer()
    for i in xrange(n):
        if bool(d.get(str(i))) != (i % 2 == 0):
            raise Exception(i)
    print 'mmap speed: %d gets per sec' % (n / (default_timer() - start_time))

def manager_test():
    n = 100000
    d = Manager().dict({str(i * 2): '1' for i in xrange(n)})
    start_time = default_timer()
    for i in xrange(n):
        if bool(d.get(str(i))) != (i % 2 == 0):
            raise Exception(i)
    print 'manager speed: %d gets per sec' % (n / (default_timer() - start_time))

def shm_test():
    n = 1000000
    d = HashTable('tmp', n)
    d.update({str(i * 2): '1' for i in xrange(n)})
    start_time = default_timer()
    for i in xrange(n):
        if bool(d.get(str(i))) != (i % 2 == 0):
            raise Exception(i)
    print 'shm speed: %d gets per sec' % (n / (default_timer() - start_time))

if __name__ == '__main__':

On my laptop performance results are:

mmap speed: 247288 gets per sec
manager speed: 33792 gets per sec
shm speed: 691332 gets per sec

simple usage example:

ht = shared_immutable_dict({'a': '1', 'b': '2'})
print ht.get('a')

How do I use the JAVA_OPTS environment variable?

Just figured it out in Oracle Java the environmental variable is called: JAVA_TOOL_OPTIONS rather than JAVA_OPTS

Python readlines() usage and efficient practice for reading

The short version is: The efficient way to use readlines() is to not use it. Ever.

I read some doc notes on readlines(), where people has claimed that this readlines() reads whole file content into memory and hence generally consumes more memory compared to readline() or read().

The documentation for readlines() explicitly guarantees that it reads the whole file into memory, and parses it into lines, and builds a list full of strings out of those lines.

But the documentation for read() likewise guarantees that it reads the whole file into memory, and builds a string, so that doesn't help.

On top of using more memory, this also means you can't do any work until the whole thing is read. If you alternate reading and processing in even the most naive way, you will benefit from at least some pipelining (thanks to the OS disk cache, DMA, CPU pipeline, etc.), so you will be working on one batch while the next batch is being read. But if you force the computer to read the whole file in, then parse the whole file, then run your code, you only get one region of overlapping work for the entire file, instead of one region of overlapping work per read.

You can work around this in three ways:

  1. Write a loop around readlines(sizehint), read(size), or readline().
  2. Just use the file as a lazy iterator without calling any of these.
  3. mmap the file, which allows you to treat it as a giant string without first reading it in.

For example, this has to read all of foo at once:

with open('foo') as f:
    lines = f.readlines()
    for line in lines:

But this only reads about 8K at a time:

with open('foo') as f:
    while True:
        lines = f.readlines(8192)
        if not lines:
        for line in lines:

And this only reads one line at a time—although Python is allowed to (and will) pick a nice buffer size to make things faster.

with open('foo') as f:
    while True:
        line = f.readline()
        if not line:

And this will do the exact same thing as the previous:

with open('foo') as f:
    for line in f:


but should the garbage collector automatically clear that loaded content from memory at the end of my loop, hence at any instant my memory should have only the contents of my currently processed file right ?

Python doesn't make any such guarantees about garbage collection.

The CPython implementation happens to use refcounting for GC, which means that in your code, as soon as file_content gets rebound or goes away, the giant list of strings, and all of the strings within it, will be freed to the freelist, meaning the same memory can be reused again for your next pass.

However, all those allocations, copies, and deallocations aren't free—it's much faster to not do them than to do them.

On top of that, having your strings scattered across a large swath of memory instead of reusing the same small chunk of memory over and over hurts your cache behavior.

Plus, while the memory usage may be constant (or, rather, linear in the size of your largest file, rather than in the sum of your file sizes), that rush of mallocs to expand it the first time will be one of the slowest things you do (which also makes it much harder to do performance comparisons).

Putting it all together, here's how I'd write your program:

for filename in os.listdir(input_dir):
    with open(filename, 'rb') as f:
        if filename.endswith(".gz"):
            f =
        words = (line.split(delimiter) for line in f)
        ... my logic ...  

Or, maybe:

for filename in os.listdir(input_dir):
    if filename.endswith(".gz"):
        f =, 'rb')
        f = open(filename, 'rb')
    with contextlib.closing(f):
        words = (line.split(delimiter) for line in f)
        ... my logic ...

Get last record of a table in Postgres

In Oracle SQL,

select * from (select row_number() over (order by rowid desc) rn, emp.* from emp) where rn=1;

curl_exec() always returns false

This happened to me yesterday and in my case was because I was following a PDF manual to develop some module to communicate with an API and while copying the link directly from the manual, for some odd reason, the hyphen from the copied link was in a different encoding and hence the curl_exec() was always returning false because it was unable to communicate with the server.

It took me a couple hours to finally understand the diference in the characters bellow:

Every time I tried to access the link directly from a browser it converted to something like

It may seem to you that they are equal but if you check the encoding of the hyphens here you'll see that the first hyphen is a unicode characters U+2010 and the other is a U+002D.

Hope this helps someone.

In Java, how do I parse XML as a String instead of a file?

I have this function in my code base, this should work for you.

public static Document loadXMLFromString(String xml) throws Exception
    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
    DocumentBuilder builder = factory.newDocumentBuilder();
    InputSource is = new InputSource(new StringReader(xml));
    return builder.parse(is);

also see this similar question

Difference between Method and Function?

well, in some programming languages they are called functions others call it methods, the fact is they are the same thing. It just represents an abstractized form of reffering to a mathematical function:

f -> f(N:N).

meaning its a function with values from natural numbers (just an example). So besides the name Its exactly the same thing, representing a block of code containing instructions in resolving your purpose.

Android changing Floating Action Button color

The document suggests that it takes the @color/accent by default. But we can override it on code by using


Also remember,

The minimum API version to use this library is 15 so you need to update it! if you dont want to do it then you need to define a custom drawable and decorate it!

How to convert DataSet to DataTable

Here is my solution:

DataTable datatable = (DataTable)dataset.datatablename;

How to install toolbox for MATLAB

For installing standard toolboxes: Just insert your CD/DVD of MATLAB and start installing, when you see typical/Custom, choose custom and check the toolboxes you want to install and uncheck the others which are installed already.

Argument Exception "Item with Same Key has already been added"

Clear the dictionary before adding any items to it. I don't know how a dictionary of one object affects another's during assignment but I got the error after creating another object with the same key,value pairs.

NB: If you are going to add items in a loop just make sure you clear the dictionary before entering the loop.

How to uninstall Apache with command line

On Windows 8.1 I had to run cmd.exe as administrator (even though I was logged in as admin). Otherwise I got an error when trying to execute: httpd.exe -k uninstall

Error: C:\Program Files\Apache\bin>(OS 5)Access is denied. : AH00373: Apache2.4: OpenS ervice failed

How to use MD5 in javascript to transmit a password

crypto-js is a rich javascript library containing many cryptography algorithms.

All you have to do is just call CryptoJS.MD5(password)

  { user: username, pass: CryptoJS.MD5(password) },
  'json' );

open new tab(window) by clicking a link in jquery

Try this:, '_blank');

This will open in new tab (if your code is synchronous and in this case it is. in other case it would open a window)

Python: Binary To Decimal Conversion

You can use int casting which allows the base specification.

int(b, 2)  # Convert a binary string to a decimal int.

Is there a Boolean data type in Microsoft SQL Server like there is in MySQL?

Use the Bit datatype. It has values 1 and 0 when dealing with it in native T-SQL

Ruby on Rails - Import Data from a CSV file

It is better to wrap the database related process inside a transaction block. Code snippet blow is a full process of seeding a set of languages to Language model,

require 'csv'

namespace :lan do
  desc 'Seed initial languages data with language & code'
  task init_data: :environment do
    puts '>>> Initializing Languages Data Table'
    ActiveRecord::Base.transaction do
      csv_path = File.expand_path('languages.csv', File.dirname(__FILE__))
      csv_str =
      csv =
      csv.each do |lan_set|
        lan_code = lan_set[0]
        lan_str = lan_set[1]
        Language.create!(language: lan_str, code: lan_code)
        print '.'
    puts ''
    puts '>>> Languages Database Table Initialization Completed'

Snippet below is a partial of languages.csv file,


Why do we need the "finally" clause in Python?

The code blocks are not equivalent. The finally clause will also be run if run_code1() throws an exception other than TypeError, or if run_code2() throws an exception, while other_code() in the first version wouldn't be run in these cases.

"unadd" a file to svn before commit

Try svn revert filename for every file you don't need and haven't yet committed. Or alternatively do svn revert -R folder for the problematic folder and then re-do the operation with correct ignoring configuration.

From the documentation:

 you can undo any scheduling operations:

$ svn add mistake.txt whoops
A         mistake.txt
A         whoops
A         whoops/oopsie.c

$ svn revert mistake.txt whoops
Reverted mistake.txt
Reverted whoops

How to resolve "Error: bad index – Fatal: index file corrupt" when using Git

You can also try for restore to previous version of the file (if you are using windows os)

How to resolve TypeError: Cannot convert undefined or null to object

In my case I had an extra pair of parenthesis ()

Instead of

export default connect(

It had to be

export default connect(

Check key exist in python dict

Use the in keyword.

if 'apples' in d:
    if d['apples'] == 20:
        print('20 apples')
        print('Not 20 apples')

If you want to get the value only if the key exists (and avoid an exception trying to get it if it doesn't), then you can use the get function from a dictionary, passing an optional default value as the second argument (if you don't pass it it returns None instead):

if d.get('apples', 0) == 20:
    print('20 apples.')
    print('Not 20 apples.')

How to select only date from a DATETIME field in MySQL?

I tried doing a SELECT DATE(ColumnName), however this does not work for TIMESTAMP columns because they are stored in UTC and the UTC date is used instead of converting to the local date. I needed to select rows that were on a specific date in my time zone, so combining my answer to this other question with Balaswamy Vaddeman's answer to this question, this is what I did:

If you are storing dates as DATETIME

Just do SELECT DATE(ColumnName)

If you are storing dates as TIMESTAMP

Load the time zone data into MySQL if you haven't done so already. For Windows servers see the previous link. For Linux, FreeBSD, Solaris, and OS X servers you would do:

mysql_tzinfo_to_sql /usr/share/zoneinfo | mysql -u root -p mysql

Then format your query like this:

SELECT DATE(CONVERT_TZ(`ColumnName`, 'UTC', 'America/New_York'))

You can also put this in the WHERE part of the query like this (but note that indexes on that column will not work):

SELECT * FROM tableName
WHERE DATE(CONVERT_TZ(`ColumnName`, 'UTC', 'America/New_York')) >= '2015-02-04'

(Obviously substitute America/New_York for your local time zone.)

The only exception to this is if your local time zone is GMT and you don't do daylight savings because your local time is the same as UTC.

PHP AES encrypt / decrypt

If you are using PHP >= 7.2 consider using inbuilt sodium core extension for encrption.

Find more information here -

Plotting time in Python with Matplotlib

7 years later and this code has helped me. However, my times still were not showing up correctly.

enter image description here

Using Matplotlib 2.0.0 and I had to add the following bit of code from Editing the date formatting of x-axis tick labels in matplotlib by Paul H.

import matplotlib.dates as mdates
myFmt = mdates.DateFormatter('%d')

I changed the format to (%H:%M) and the time displayed correctly. enter image description here

All thanks to the community.

what's data-reactid attribute in html?

That's the HTML data attribute. See this for more detail:

Basically it's just a container of your custom data while still making the HTML valid. It's data- plus some unique identifier.

How to add button inside input

Use a Flexbox, and put the border on the form.

The best way to do this now (2019) is with a flexbox.

  • Put the border on the containing element (in this case I've used the form, but you could use a div).
  • Use a flexbox layout to arrange the input and the button side by side. Allow the input to stretch to take up all available space.
  • Now hide the input by removing its border.

Run the snippet below to see what you get.

form {_x000D_
  /* This bit sets up the horizontal layout */_x000D_
  /* This bit draws the box around it */_x000D_
  border:1px solid grey;_x000D_
  /* I've used padding so you can see the edges of the elements. */_x000D_
input {_x000D_
  /* Tell the input to use all the available space */_x000D_
  /* And hide the input's outline, so the form looks like the outline */_x000D_
input:focus {_x000D_
  /* removing the input focus blue box. Put this on the form if you like. */_x000D_
  outline: none;_x000D_
button {_x000D_
  /* Just a little styling to make it pretty */_x000D_
  border:1px solid blue;_x000D_
  <input />_x000D_

Why this is good

  • It will stretch to any width.
  • The button will always be just as big as it needs to be. It won't stretch if the screen is wide, or shrink if the screen is narrow.
  • The input text will not go behind the button.

Caveats and Browser Support

There's limited Flexbox support in IE9, so the button will not be on the right of the form. IE9 has not been supported by Microsoft for some years now, so I'm personally quite comfortable with this.

I've used minimal styling here. I've left in the padding to show the edges of things. You can obviously make this look however you want it to look with rounded corners, drop shadows, etc..

How can I remove jenkins completely from linux

First - stop Jenkins service:

sudo service jenkins stop

Next - delete:

sudo apt-get remove --purge jenkins

If you used separate server for Jenkins, some GCP or AWS - just delete this server. Here is a video how to uninstall Jenkins from GCP Compute Engine

did you register the component correctly? For recursive components, make sure to provide the "name" option

In my case, i was calling twice the import...

@click="$router.push({ path: 'searcherresult' })"

import SearcherResult from "../views/SearcherResult"; --- ERROR

Cause i call in other component...

How can I color Python logging output?

You can import the colorlog module and use its ColoredFormatter for colorizing log messages.


Boilerplate for main module:

import logging
import os
import sys
    import colorlog
except ImportError:

def setup_logging():
    root = logging.getLogger()
    format      = '%(asctime)s - %(levelname)-8s - %(message)s'
    date_format = '%Y-%m-%d %H:%M:%S'
    if 'colorlog' in sys.modules and os.isatty(2):
        cformat = '%(log_color)s' + format
        f = colorlog.ColoredFormatter(cformat, date_format,
              log_colors = { 'DEBUG'   : 'reset',       'INFO' : 'reset',
                             'WARNING' : 'bold_yellow', 'ERROR': 'bold_red',
                             'CRITICAL': 'bold_red' })
        f = logging.Formatter(format, date_format)
    ch = logging.StreamHandler()

log = logging.getLogger(__name__)

The code only enables colors in log messages, if the colorlog module is installed and if the output actually goes to a terminal. This avoids escape sequences being written to a file when the log output is redirected.

Also, a custom color scheme is setup that is better suited for terminals with dark background.

Some example logging calls:

log.debug   ('Hello Debug')    ('Hello Info')
log.warn    ('Hello Warn')
log.error   ('Hello Error')
log.critical('Hello Critical')


enter image description here

How to give a pattern for new line in grep?

just found

grep $'\r'

It's using $'\r' for c-style escape in Bash.

in this article

Map.Entry: How to use it?

This code is better rewritten as:

for( Map.Entry me : entrys.entrySet() )
    this.add( (Component) me.getValue() );

and it is equivalent to:

for( Component comp : entrys.getValues() )
    this.add( comp );

When you enumerate the entries of a map, the iteration yields a series of objects which implement the Map.Entry interface. Each one of these objects contains a key and a value.

It is supposed to be slightly more efficient to enumerate the entries of a map than to enumerate its values, but this factoid presumes that your Map is a HashMap, and also presumes knowledge of the inner workings (implementation details) of the HashMap class. What can be said with a bit more certainty is that no matter how your map is implemented, (whether it is a HashMap or something else,) if you need both the key and the value of the map, then enumerating the entries is going to be more efficient than enumerating the keys and then for each key invoking the map again in order to look up the corresponding value.

Regex lookahead, lookbehind and atomic groups


Given the string foobarbarfoo:

bar(?=bar)     finds the 1st bar ("bar" which has "bar" after it)
bar(?!bar)     finds the 2nd bar ("bar" which does not have "bar" after it)
(?<=foo)bar    finds the 1st bar ("bar" which has "foo" before it)
(?<!foo)bar    finds the 2nd bar ("bar" which does not have "foo" before it)

You can also combine them:

(?<=foo)bar(?=bar)    finds the 1st bar ("bar" with "foo" before it and "bar" after it)


Look ahead positive (?=)

Find expression A where expression B follows:


Look ahead negative (?!)

Find expression A where expression B does not follow:


Look behind positive (?<=)

Find expression A where expression B precedes:


Look behind negative (?<!)

Find expression A where expression B does not precede:


Atomic groups (?>)

An atomic group exits a group and throws away alternative patterns after the first matched pattern inside the group (backtracking is disabled).

  • (?>foo|foot)s applied to foots will match its 1st alternative foo, then fail as s does not immediately follow, and stop as backtracking is disabled

A non-atomic group will allow backtracking; if subsequent matching ahead fails, it will backtrack and use alternative patterns until a match for the entire expression is found or all possibilities are exhausted.

  • (foo|foot)s applied to foots will:

    1. match its 1st alternative foo, then fail as s does not immediately follow in foots, and backtrack to its 2nd alternative;
    2. match its 2nd alternative foot, then succeed as s immediately follows in foots, and stop.

Some resources

Online testers

How to declare an array of objects in C#

Everything you have looks fine.

The only thing I can think of (without seeing the error message, which you should have provided), is that GameObject needs a default (no parameter) constructor.

Why do I get a warning icon when I add a reference to an MEF plugin project?

I had created a new .sln which was put in a subfolder. The .nuget folder was missing from where that .sln file was added. Moving the .nuget folder from the root into the subfolder where my new .sln file was solved the issue for me.

I came back later and added the .sln file to the root and deleted the subfolder. Doing this originally would have solved the issue as well.

convert double to int

Convert.ToInt32 is the best way to convert

Conditionally Remove Dataframe Rows with R

Logic index:

d<-d[!(d$A=="B" & d$E==0),]

How to run a Python script in the background even after I logout SSH?

If you've already started the process, and don't want to kill it and restart under nohup, you can send it to the background, then disown it.

Ctrl+Z (suspend the process)

bg (restart the process in the background

disown %1 (assuming this is job #1, use jobs to determine)

How to open the Google Play Store directly from my Android application?

Ready-to-use solution:

public class GoogleServicesUtils {

    public static void openAppInGooglePlay(Context context) {
        final String appPackageName = context.getPackageName();
        try {
            context.startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse("market://details?id=" + appPackageName)));
        } catch (android.content.ActivityNotFoundException e) { // if there is no Google Play on device
            context.startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse("" + appPackageName)));


Based on Eric's answer.

Python: Pandas pd.read_excel giving ImportError: Install xlrd >= 0.9.0 for Excel support

Please make sure your python or python3 can see xlrd installation. I had a situation where python3.5 and python3.7 were installed in two different locations. While xlrd was installed with python3.5, I was using python3 (from python3.7 dir) to run my script and got the same error reported above. When I used the correct python (viz. python3.5 dir) to run my script, I was able to read the excel spread sheet without a problem.

PHP salt and hash SHA256 for login password

I think @Flo254 chained $salt to $password1and stored them to $hashed variable. $hashed variable goes inside INSERT query with $salt.

Convert ascii char[] to hexadecimal char[] in C

#include <stdio.h>
#include <string.h>

int main(void){
    char word[17], outword[33];//17:16+1, 33:16*2+1
    int i, len;

    printf("Intro word:");
    fgets(word, sizeof(word), stdin);
    len = strlen(word);
        word[--len] = '\0';

    for(i = 0; i<len; i++){
        sprintf(outword+i*2, "%02X", word[i]);
    printf("%s\n", outword);
    return 0;

Password must have at least one non-alpha character

A simple method will be like this:

Match match1 = Regex.Match(<input_string>, @"(?=.{7})");   

match1.Success ensures that there are at least 8 characters.

Match match2 = Regex.Match(<input_string>, [^a-zA-Z]);

match2.Success ensures that there is at least one special character or number within the string.

So, match1.Success && match2.Success guarantees will get what you want.

Multiple IF statements between number ranges

standalone one cell solution based on VLOOKUP

US syntax:

        IF(A2:A>2000, "More than 2000",VLOOKUP(A2:A,
 {{(TRANSPOSE({{{0;   "Less than 500"},
               {500;  "Between 500 and 1000"}},
              {{1000; "Between 1000 and 1500"},
               {1500; "Between 1500 and 2000"}}}))}}, 2)),)), )

EU syntax:

        IF(A2:A>2000; "More than 2000";VLOOKUP(A2:A;
 {{(TRANSPOSE({{{0;   "Less than 500"}\
               {500;  "Between 500 and 1000"}}\
              {{1000; "Between 1000 and 1500"}\
               {1500; "Between 1500 and 2000"}}}))}}; 2));)); )


How to remove commits from a pull request

So do the following ,

Lets say your branch name is my_branch and this has the extra commits.

  1. git checkout -b my_branch_with_extra_commits (Keeping this branch saved under a different name)
  2. gitk (Opens git console)
  3. Look for the commit you want to keep. Copy the SHA of that commit to a notepad.
  4. git checkout my_branch
  5. gitk (This will open the git console )
  6. Right click on the commit you want to revert to (State before your changes) and click on "reset branch to here"
  7. Do a git pull --rebase origin branch_name_to _merge_to
  8. git cherry-pick <SHA you copied in step 3. >

Now look at the local branch commit history and make sure everything looks good.

Bootstrap 4 - Glyphicons migration?

The glyphicons.less file from Bootstrap 3 is available on GitHub.

It needs these variables:

@icon-font-path:          "../fonts/";
@icon-font-name:          "glyphicons-halflings-regular";
@icon-font-svg-id:        "glyphicons_halflingsregular";

Then you can convert the .less file to a .css file which you can use directly. You can do this online on Here I've done it for you, save it as glyphicons.css and include it in your HTML files.

<link href="/Content/glyphicons.css" rel="stylesheet" />

You also need the Glyphicon fonts which is in the Bootstrap 3 package, place them in a /fonts/ directory.

Now you can just keep on using Glyphicons with Bootstrap 4 as usual.

How to dynamically insert a <script> tag via jQuery after page load?

This answer is technically similar or equal to what jcoffland answered. I just added a query to detect if a script is already present or not. I need this because I work in an intranet website with a couple of modules, of which some are sharing scripts or bring their own, but these scripts do not need to be loaded everytime again. I am using this snippet since more than a year in production environment, it works like a charme. Commenting to myself: Yes I know, it would be more correct to ask if a function exists... :-)

if (!$('head > script[src="js/jquery.searchable.min.js"]').length) {
    $('head').append($('<script />').attr('src','js/jquery.searchable.min.js'));

How to call two methods on button's onclick method in HTML or JavaScript?


You can also do as like below... In this way, your both functions should call and if both functions return true then it will return true else return false.

<input type="button" 
     onclick="var valFunc1 = func1(); var valFunc2 = func2(); if(valFunc1 == true && valFunc2 ==true) {return true;} else{return false;}" 
     value="Call2Functions" />

Thank you, Vishal Patel

String date to xmlgregoriancalendar conversion

For me the most elegant solution is this one:

XMLGregorianCalendar result = DatatypeFactory.newInstance()

Using Java 8.

Extended example:

XMLGregorianCalendar result = DatatypeFactory.newInstance()

This prints out:


Using NOT operator in IF conditions

It really depends on what you're trying to accomplish. If you have no else clause then if(!doSomething()) seems fine. However, if you have

if(!doSomething()) {
else {
    // do something else

I'd probably reverse that logic to remove the ! operator and make the if clause slightly more clear.

How to merge a specific commit in Git

'git cherry-pick' should be your answer here.

Apply the change introduced by an existing commit.

Do not forget to read bdonlan's answer about the consequence of cherry-picking in this post:
"Pull all commits from a branch, push specified commits to another", where:




The problem with this commit is that git considers commits to include all history before them

Where C' has a different SHA-1 ID.
Likewise, cherry picking a commit from one branch to another basically involves generating a patch, then applying it, thus losing history that way as well.

This changing of commit IDs breaks git's merging functionality among other things (though if used sparingly there are heuristics that will paper over this).
More importantly though, it ignores functional dependencies - if C actually used a function defined in B, you'll never know.

Javascript event handler with parameters

Something you can try is using the bind method, I think this achieves what you were asking for. If nothing else, it's still very useful.

function doClick(elem, func) {
  var diffElem = document.getElementById('some_element'); //could be the same or different element than the element in the doClick argument
  diffElem.addEventListener('click', func.bind(diffElem, elem))

function clickEvent(elem, evt) {
  // 'this' and elem can be the same thing if the first parameter 
  // of the bind method is the element the event is being attached to from the argument passed to doClick

var elem = document.getElementById('elem_to_do_stuff_with');
doClick(elem, clickEvent);

What's the fastest way to read a text file line-by-line?

If the file size is not big, then it is faster to read the entire file and split it afterwards

var filestreams = sr.ReadToEnd().Split(Environment.NewLine, 

Check if EditText is empty.

You could call this function for each of the edit texts:

public boolean isEmpty(EditText editText) {
    boolean isEmptyResult = false;
    if (editText.getText().length() == 0) {
        isEmptyResult = true;
    return isEmptyResult;

Cross-Origin Request Headers(CORS) with PHP headers

this should work

header("Access-Control-Allow-Origin: *");
header("Access-Control-Allow-Headers: X-Requested-With, Content-Type, Origin, Cache-Control, Pragma, Authorization, Accept, Accept-Encoding");

If input field is empty, disable submit button

For those that use coffeescript, I've put the code we use globally to disable the submit buttons on our most widely used form. An adaption of Adil's answer above.

$('#new_post button').prop 'disabled', true
$('#new_post #post_message').keyup ->
    $('#new_post button').prop 'disabled', if @value == '' then true else false

How do I launch a program from command line without opening a new cmd window?

1-Open you folder that contains your application in the File Explorer. 2-Press SHIFT and Right Click in White Space. 3-Click on "Open command window here". 4-Run your application. (you can type some of the first characters of application name and press Up Arrow Key OR Down Arrow Key)

UITextField border color

this question shows up pretty high on a Google search and worked for the most part! I did find that Salman Zaidi's answer was partially correct for iOS 7.

You need to make a modification to the "reverting" code. I found that the following for reverting worked perfectly:

textField.layer.cornerRadius = 0.0f;
textField.layer.masksToBounds = YES;
textField.layer.borderColor = [[UIColor blackColor] CGColor];
textField.layer.borderWidth = 0.0f;

I understand that this is most likely due to changes in iOS 7.

java.sql.SQLException: No suitable driver found for jdbc:mysql://localhost:3306/dbname

You have to load jdbc driver. Consider below Code.

try {

            // connect way #1
            String url1 = "jdbc:mysql://localhost:3306/aavikme";
            String user = "root";
            String password = "aa";

            conn1 = DriverManager.getConnection(url1, user, password);
            if (conn1 != null) {
                System.out.println("Connected to the database test1");

            // connect way #2
            String url2 = "jdbc:mysql://localhost:3306/aavikme?user=root&password=aa";
            conn2 = DriverManager.getConnection(url2);
            if (conn2 != null) {
                System.out.println("Connected to the database test2");

            // connect way #3
            String url3 = "jdbc:mysql://localhost:3306/aavikme";
            Properties info = new Properties();
            info.put("user", "root");
            info.put("password", "aa");

            conn3 = DriverManager.getConnection(url3, info);
            if (conn3 != null) {
                System.out.println("Connected to the database test3");
   } catch (SQLException ex) {
            System.out.println("An error occurred. Maybe user/password is invalid");
   } catch (ClassNotFoundException e) {
    // TODO Auto-generated catch block

XAMPP keeps showing Dashboard/Welcome Page instead of the Configuration Page

This works in Windows; didn't check Linux but don't see why it wouldn't work. Download the zip files for 5.6.8 portable. Unzip the files and copy the xampp/htdocs to the xampp/htdocs in your install directory.

How to get your Netbeans project into Eclipse

There's a very easy way if you were using a web application just follow this link.

just do in eclipse :

File > import > web > war file

Then select the war file of your app :)) very easy !!

Error: fix the version conflict (google-services plugin)

After All Working for 6 hours i got the solution...

Simple Just what ever the plugins you defined in the build.gradle file... for ex: google services plugins or firebase plugins or any third party plugins all the **version code** should be same..

Example: In my application i am using following plugins...

    // google services plugins
    implementation ''
    implementation ''
    implementation ''
    implementation ''

    //firebase plugin
    implementation ''

    //Third Party plugin
    implementation ''

In the above plugins version code(ex:10.0.1, 16.0.0, 11.6.1) are different I was facing fix the version conflict (google-services plugin) issue

Below for all plugins i have given single version code(11.6.0) and the issue is resovled...

 // google services plugins
    implementation ''
    implementation ''
    implementation ''
    implementation ''

    //firebase plugin
    implementation ''

    //Third Party plugin
    implementation ''

**Syn Gradle**...

Go to Build>>Rebuild Projcet...

Sure it will work....@Ambilpura

Run script on mac prompt "Permission denied"

In my case, I had made a stupid typo in the shebang.

So in case someone else on with fat fingers stumbles across this question:

Whoops: #!/usr/local/bin ruby

I meant to write: #!/usr/bin/env ruby

The vague error ZSH gives sent me down the wrong path:

ZSH: zsh: permission denied: ./foo.rb

Bash: bash: ./foo.rb: /usr/local/bin: bad interpreter: Permission denied

Custom Date/Time formatting in SQL Server

Not answering your question specifically, but isn't that something that should be handled by the presentation layer of your application. Doing it the way you describe creates extra processing on the database end as well as adding extra network traffic (assuming the database exists on a different machine than the application), for something that could be easily computed on the application side, with more rich date processing libraries, as well as being more language agnostic, especially in the case of your first example which contains the abbreviated month name. Anyway the answers others give you should point you in the right direction if you still decide to go this route.

How to check if a file is a valid image file?

One option is to use the filetype package.


python -m pip install filetype


  1. Quick: Does its work by loading the first few bytes of your image (check on the magic number)
  2. Supports different mime type: Images, Videos, Fonts, Audio, Archives.


filetype >= 1.0.7

import filetype

filename = "/path/to/file.jpg"

if filetype.is_image(filename):
    print(f"{filename} is a valid image...")
elif filetype.is_video(filename):
    print(f"{filename} is a valid video...")

filetype <= 1.0.6

import filetype

filename = "/path/to/file.jpg"

if filetype.image(filename):
    print(f"{filename} is a valid image...")
    print(f"{filename} is a valid video...")

Additional information on the official repo:

Check with jquery if div has overflowing elements

Here's a pure jQuery solution, but it's rather messy:

var div_height = $(this).height();
var vertical_div_top_position = $(this).offset().top;
var lastchild_height = $(this).children('p:last-child').height();
var vertical_lastchild_top_position = $(this).children('p:last-child').offset().top;
var vertical_lastchild_bottom_position = lastchild_height + vertical_lastchild_top_position;
var real_height = vertical_lastchild_bottom_position - vertical_div_top_position;

if (real_height > div_height){
    //overflow div

Is it a good practice to place C++ definitions in header files?

What might be informing you coworker is a notion that most C++ code should be templated to allow for maximum usability. And if it's templated, then everything will need to be in a header file, so that client code can see it and instantiate it. If it's good enough for Boost and the STL, it's good enough for us.

I don't agree with this point of view, but it may be where it's coming from.

git rm - fatal: pathspec did not match any files

In your case, use git filter-branch instead of git rm.

git rm will delete the files in the sense that they will not be tracked by git anymore, but that does not remove the old commit objects corresponding to those images, and so you will still be stuck with pushing the earlier commits which correspond to 12GB of images.

The git filter-branch, on the other hand, can remove those files from all the previous commits as well, thus doing away with the need to push any of them.

  1. Use the command

    git filter-branch --force --index-filter \
      'git rm -r --cached --ignore-unmatch public/photos' \
      --prune-empty --tag-name-filter cat -- --all
  2. After the filter branch is complete, verify that no unintended file was lost.

  3. Now add a .gitignore rule

    echo public/photos >> .gitignore
    git add .gitignore && git commit -m "ignore rule for photos"
  4. Now do a push

    git push -f origin branch

Check this, this and this for further help. Just to be on the safer side, I would suggest you create a backup copy of the repo on your system before going ahead with these instructions.

As for your orignial error message, it is happening because you already untracked them using git rm, and hence git is complaining because it can't remove a file it isn't tracking. Read more about this here.

Create the perfect JPA entity

I'll try to answer several key points: this is from long Hibernate/ persistence experience including several major applications.

Entity Class: implement Serializable?

Keys needs to implement Serializable. Stuff that's going to go in the HttpSession, or be sent over the wire by RPC/Java EE, needs to implement Serializable. Other stuff: not so much. Spend your time on what's important.

Constructors: create a constructor with all required fields of the entity?

Constructor(s) for application logic, should have only a few critical "foreign key" or "type/kind" fields which will always be known when creating the entity. The rest should be set by calling the setter methods -- that's what they're for.

Avoid putting too many fields into constructors. Constructors should be convenient, and give basic sanity to the object. Name, Type and/or Parents are all typically useful.

OTOH if application rules (today) require a Customer to have an Address, leave that to a setter. That is an example of a "weak rule". Maybe next week, you want to create a Customer object before going to the Enter Details screen? Don't trip yourself up, leave possibility for unknown, incomplete or "partially entered" data.

Constructors: also, package private default constructor?

Yes, but use 'protected' rather than package private. Subclassing stuff is a real pain when the necessary internals are not visible.


Use 'property' field access for Hibernate, and from outside the instance. Within the instance, use the fields directly. Reason: allows standard reflection, the simplest & most basic method for Hibernate, to work.

As for fields 'immutable' to the application -- Hibernate still needs to be able to load these. You could try making these methods 'private', and/or put an annotation on them, to prevent application code making unwanted access.

Note: when writing an equals() function, use getters for values on the 'other' instance! Otherwise, you'll hit uninitialized/ empty fields on proxy instances.

Protected is better for (Hibernate) performance?



This is relevant to working with entities, before they've been saved -- which is a thorny issue. Hashing/comparing on immutable values? In most business applications, there aren't any.

A customer can change address, change the name of their business, etc etc -- not common, but it happens. Corrections also need to be possible to make, when the data was not entered correctly.

The few things that are normally kept immutable, are Parenting and perhaps Type/Kind -- normally the user recreates the record, rather than changing these. But these do not uniquely identify the entity!

So, long and short, the claimed "immutable" data isn't really. Primary Key/ ID fields are generated for the precise purpose, of providing such guaranteed stability & immutability.

You need to plan & consider your need for comparison & hashing & request-processing work phases when A) working with "changed/ bound data" from the UI if you compare/hash on "infrequently changed fields", or B) working with "unsaved data", if you compare/hash on ID.

Equals/HashCode -- if a unique Business Key is not available, use a non-transient UUID which is created when the entity is initialized

Yes, this is a good strategy when required. Be aware that UUIDs are not free, performance-wise though -- and clustering complicates things.

Equals/HashCode -- never refer to related entities

"If related entity (like a parent entity) needs to be part of the Business Key then add a non insertable, non updatable field to store the parent id (with the same name as the ManytoOne JoinColumn) and use this id in the equality check"

Sounds like good advice.

Hope this helps!

Launch Failed. Binary not found. CDT on Eclipse Helios

First you need to make sure that the project has been built. You can build a project with the hammer icon in the toolbar. You can choose to build either a Debug or Release version. If you cannot build the project then the problem is that you either don't have a compiler installed or that the IDE does not find the compiler.

To see if you have a compiler installed in a Mac you can run the following command from the command line:

g++ --version

If you have it already installed (it gets installed when you install the XCode tools) you can see its location running:

which g++

If you were able to build the project but you still get the "binary not found" message then the issue might be that a default launch configuration is not being created for the project. In that case do this:

Right click project > Run As > Run Configurations... > 

Then create a new configuration under the "C/C++ Application" section > Enter the full path to the executable file (the file that was created in the build step and that will exist in either the Debug or Release folder). Your launch configuration should look like this:

enter image description here

AngularJS: ng-show / ng-hide not working with `{{ }}` interpolation

remove {{}} braces around because angular expressions cannot be used in angular directives.

For More:


  <body ng-app="changeExample">
    <div ng-controller="ExampleController">
    <p ng-show="">I could be shown, or I could be hidden</p>
    <p ng-hide="">I could be shown, or I could be hidden</p>

     angular.module('changeExample', [])
        .controller('ExampleController', ['$scope', function($scope) {
          $ ={};
          $ = true;

How to solve "Could not establish trust relationship for the SSL/TLS secure channel with authority"

In addition to the answers above, you could encounter this error if your client is running the wrong TLS version, for example if the server is only running TLS 1.2.

You can fix it by using:

// tested in .NET 4.5:
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

Merge, update, and pull Git branches without using checkouts

As Amber said, fast-forward merges are the only case in which you could conceivably do this. Any other merge conceivably needs to go through the whole three-way merge, applying patches, resolving conflicts deal - and that means there need to be files around.

I happen to have a script around I use for exactly this: doing fast-forward merges without touching the work tree (unless you're merging into HEAD). It's a little long, because it's at least a bit robust - it checks to make sure that the merge would be a fast-forward, then performs it without checking out the branch, but producing the same results as if you had - you see the diff --stat summary of changes, and the entry in the reflog is exactly like a fast forward merge, instead of the "reset" one you get if you use branch -f. If you name it git-merge-ff and drop it in your bin directory, you can call it as a git command: git merge-ff.


_usage() {
    echo "Usage: git merge-ff <branch> <committish-to-merge>" 1>&2
    exit 1

_merge_ff() {

    branch_orig_hash="$(git show-ref -s --verify refs/heads/$branch 2> /dev/null)"
    if [ $? -ne 0 ]; then
        echo "Error: unknown branch $branch" 1>&2

    commit_orig_hash="$(git rev-parse --verify $commit 2> /dev/null)"
    if [ $? -ne 0 ]; then
        echo "Error: unknown revision $commit" 1>&2

    if [ "$(git symbolic-ref HEAD)" = "refs/heads/$branch" ]; then
        git merge $quiet --ff-only "$commit"
        if [ "$(git merge-base $branch_orig_hash $commit_orig_hash)" != "$branch_orig_hash" ]; then
            echo "Error: merging $commit into $branch would not be a fast-forward" 1>&2
            exit 1
        echo "Updating ${branch_orig_hash:0:7}..${commit_orig_hash:0:7}"
        if git update-ref -m "merge $commit: Fast forward" "refs/heads/$branch" "$commit_orig_hash" "$branch_orig_hash"; then
            if [ -z $quiet ]; then
                echo "Fast forward"
                git diff --stat "$branch@{1}" "$branch"
            echo "Error: fast forward using update-ref failed" 1>&2

while getopts "q" opt; do
    case $opt in
        q ) quiet="-q";;
        * ) ;;
shift $((OPTIND-1))

case $# in
    2 ) _merge_ff "$1" "$2";;
    * ) _usage

P.S. If anyone sees any issues with that script, please comment! It was a write-and-forget job, but I'd be happy to improve it.

Trust Anchor not found for Android SSL Connection

**Set proper alias name**
CertificateFactory certificateFactory = CertificateFactory.getInstance("X.509","BC");
            X509Certificate cert = (X509Certificate) certificateFactory.generateCertificate(derInputStream);
            String alias = cert.getSubjectX500Principal().getName();
KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType());
trustStore.setCertificateEntry(alias, cert);

sql primary key and index

You are right, it's confusing that SQL Server allows you to create duplicate indexes on the same field(s). But the fact that you can create another doesn't indicate that the PK index doesn't also already exist.

The additional index does no good, but the only harm (very small) is the additional file size and row-creation overhead.

How do you check for permissions to write to a directory or file?

When your code does the following:

  1. Checks the current user has permission to do something.
  2. Carries out the action that needs the entitlements checked in 1.

You run the risk that the permissions change between 1 and 2 because you can't predict what else will be happening on the system at runtime. Therefore, your code should handle the situation where an UnauthorisedAccessException is thrown even if you have previously checked permissions.

Note that the SecurityManager class is used to check CAS permissions and doesn't actually check with the OS whether the current user has write access to the specified location (through ACLs and ACEs). As such, IsGranted will always return true for locally running applications.

Example (derived from Josh's example):

//1. Provide early notification that the user does not have permission to write.
FileIOPermission writePermission = new FileIOPermission(FileIOPermissionAccess.Write, filename);
    //No permission. 
    //Either throw an exception so this can be handled by a calling function
    //or inform the user that they do not have permission to write to the folder and return.

//2. Attempt the action but handle permission changes.
    using (FileStream fstream = new FileStream(filename, FileMode.Create))
    using (TextWriter writer = new StreamWriter(fstream))
catch (UnauthorizedAccessException ex)
    //No permission. 
    //Either throw an exception so this can be handled by a calling function
    //or inform the user that they do not have permission to write to the folder and return.

It's tricky and not recommended to try to programatically calculate the effective permissions from the folder based on the raw ACLs (which are all that are available through the System.Security.AccessControl classes). Other answers on Stack Overflow and the wider web recommend trying to carry out the action to know whether permission is allowed. This post sums up what's required to implement the permission calculation and should be enough to put you off from doing this.

Do we have router.reload in vue-router?


why don't you use forceUpdate method?

How to call a function in shell Scripting?

You don't specify which shell (there are many), so I am assuming Bourne Shell, that is I think your script starts with:


Please remember to tag future questions with the shell type, as this will help the community answer your question.

You need to define your functions before you call them. Using ():

    echo "Performing process_install() commands, using arguments [${*}]..."

    echo "Performing process_exit() commands, using arguments [${*}]..."

Then you can call your functions, just as if you were calling any command:

if [ "$choice" = "true" ]
    process_install foo bar
elif [ "$choice" = "false" ]
    process_exit baz qux

You may also wish to check for invalid choices at this juncture...

    echo "Invalid choice [${choice}]..."

See it run with three different values of ${choice}.

Good luck!

How to resolve git status "Unmerged paths:"?

All you should need to do is:

# if the file in the right place isn't already committed:
git add <path to desired file>

# remove the "both deleted" file from the index:
git rm --cached ../public/images/originals/

# commit the merge:
git commit

How comment a JSP expression?

One of:

In html

<!-- map.size here because --> 
<%= map.size() %>

theoretically the following should work, but i never used it this way.

<%= map.size() // map.size here because %>

What does "Object reference not set to an instance of an object" mean?

In a nutshell it means.. You are trying to access an object without instantiating it.. You might need to use the "new" keyword to instantiate it first i.e create an instance of it.

For eg:

public class MyClass
   public int Id {get; set;}

MyClass myClass;

myClass.Id = 0; <----------- An error will be thrown here.. because myClass is null here...

You will have to use:

myClass = new MyClass();
myClass.Id = 0;

Hope I made it clear..

Add characters to a string in Javascript

var text ="";
for (var member in list) {
        text += list[member];

Remove object from a list of objects in python

You could try this to dynamically remove an object from an array without looping through it? Where e and t are just random objects.

>>> e = {'b':1, 'w': 2}
>>> t = {'b':1, 'w': 3}
>>> p = [e,t]
>>> p
[{'b': 1, 'w': 2}, {'b': 1, 'w': 3}]
>>> p.pop(p.index({'b':1, 'w': 3}))
{'b': 1, 'w': 3}
>>> p
[{'b': 1, 'w': 2}]

How to run a cron job inside a docker container?

Another route you can take is Ofelia, which is a highly configurable task runner image that allows 4 modes of execution.

job-exec: this job is executed inside of a running container.
job-run: runs a command inside of a new container, using a specific image.
job-local: runs the command inside of the host running ofelia.
job-service-run: runs the command inside a new "run-once" service, for running inside a swarm

The advantage here is that somebody else has done all the heavy lifting for you. Super convenient and easy.

It also has a spiffy official mascot.

enter image description here

Print in new line, java

System.out.print(values[i] + " ");
//in one number be printed

error: No resource identifier found for attribute 'adSize' in package '' main.xml

Replace /res/ with /lib/ in your custom layout nampespace.


in your case, would be:


I hope it helps.

SQL Server stored procedure creating temp table and inserting value

A SELECT INTO statement creates the table for you. There is no need for the CREATE TABLE statement before hand.

What is happening is that you create #ivmy_cash_temp1 in your CREATE statement, then the DB tries to create it for you when you do a SELECT INTO. This causes an error as it is trying to create a table that you have already created.

Either eliminate the CREATE TABLE statement or alter your query that fills it to use INSERT INTO SELECT format.

If you need a unique ID added to your new row then it's best to use SELECT INTO... since IDENTITY() only works with this syntax.

how to set default culture info for entire c# application

With 4.0, you will need to manage this yourself by setting the culture for each thread as Alexei describes. But with 4.5, you can define a culture for the appdomain and that is the preferred way to handle this. The relevant apis are CultureInfo.DefaultThreadCurrentCulture and CultureInfo.DefaultThreadCurrentUICulture.

For a boolean field, what is the naming convention for its getter/setter?

Maybe it is time to start revising this answer? Personally I would vote for setActive() and unsetActive() (alternatives can be setUnActive(), notActive(), disable(), etc. depending on context) since "setActive" implies you activate it at all times, which you don't. It's kind of counter intuitive to say "setActive" but actually remove the active state.

Another problem is, you can can not listen to specifically a SetActive event in a CQRS way, you would need to listen to a 'setActiveEvent' and determine inside that listener wether is was actually set active or not. Or of course determine which event to call when calling setActive() but that then goes against the Separation of Concerns principle.

A good read on this is the FlagArgument article by Martin Fowler:

However, I come from a PHP background and see this trend being adopted more and more. Not sure how much this lives with Java development.

How to fully clean bin and obj folders within Visual Studio?

I use VisualStudioClean which is easy to understand and predictable. Knowing how it works and what files it is going to delete relieves me.

Previously I tried VSClean (note VisualStudioClean is not VSClean), VSClean is more advanced, it has many configurations that sometimes makes me wondering what files it is going to delete? One mis-configuration will result in lose of my source codes. Testing how the configuration will work need backing up all my projects which take a lot of times, so in the end I choose VisualStudioClean instead.

Conclusion : VisualStudioClean if you want basic cleaning, VSClean for more complex scenario.

What possibilities can cause "Service Unavailable 503" error?

We recently encountered this error, root cause turned out to be an expired SSL cert on the IIS server. The Load Balancer (infront of our web tier) found the SSL expired, and instead of handling the HTTP traffic over to one of the IIS servers, started showing this error. So basically IIS unable to server requests, for a totally different reason :)

Show week number with Javascript?

If you want something that works and is future-proof, use a library like MomentJS.


throwing an exception in objective-c/cocoa

You should only throw exceptions if you find yourself in a situation that indicates a programming error, and want to stop the application from running. Therefore, the best way to throw exceptions is using the NSAssert and NSParameterAssert macros, and making sure that NS_BLOCK_ASSERTIONS is not defined.

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 use onResume()?

onResume() is one of the methods called throughout the activity lifecycle. onResume() is the counterpart to onPause() which is called anytime an activity is hidden from view, e.g. if you start a new activity that hides it. onResume() is called when the activity that was hidden comes back to view on the screen.

You're question asks abou what method is used to restart an activity. onCreate() is called when the activity is first created. In practice, most activities persist in the background through a series of onPause() and onResume() calls. An activity is only really "restarted" by onRestart() if it is first fully stopped by calling onStop() and then brought back to life. Thus if you are not actually stopping activities with onStop() it is most likley you will be using onResume().

Read the android doc in the above link to get a better understanding of the relationship between the different lifestyle methods. Regardless of which lifecycle method you end up using the general format is the same. You must override the standard method and include your code, i.e. what you want the activity to do at that point, in the commented section.

public void onResume(){
 //will be executed onResume

How to use addTarget method in swift 3

Yes, don't add "()" if there is no param

button.addTarget(self, action:#selector(handleRegister), for: .touchUpInside). 

and if you want to get the sender

button.addTarget(self, action:#selector(handleRegister(_:)), for: .touchUpInside). 

func handleRegister(sender: UIButton){


button.addTarget(self, action:#selector(handleRegister(_:)), for: .touchUpInside)

no longer works, you need to replace _ in the selector with a variable name you used in the function header, in this case it would be sender, so the working code becomes:

button.addTarget(self, action:#selector(handleRegister(sender:)), for: .touchUpInside)

PHP's array_map including keys

I made this function, based on eis's answer:

function array_map_($callback, $arr) {
    if (!is_callable($callback))
        return $arr;

    $result = array_walk($arr, function(&$value, $key) use ($callback) {
        $value = call_user_func($callback, $key, $value);

    if (!$result)
        return false;

    return $arr;


$test_array = array("first_key" => "first_value", 
                "second_key" => "second_value");

var_dump(array_map_(function($key, $value){
    return $key . " loves " . $value;
}, $arr));


array (
  'first_key' => 'first_key loves first_value,
  'second_key' => 'second_key loves second_value',

Off course, you can use array_values to return exactly what OP wants.

array_values(array_map_(function($key, $value){
    return $key . " loves " . $value;
}, $test_array))

iTunes Connect Screenshots Sizes for all iOS (iPhone/iPad/Apple Watch) devices

Also - please note that you may have transparency set even if you don't actually have any transparency in your images. If you're using photoshop, 'save for web' and de-select 'transparency' or just convert your image to a .jpg. iTunes Connect seems to reject transparencies as well.

Brew install docker does not include docker engine?

Please try running

brew install docker

This will install the Docker engine, which will require Docker-Machine (+ VirtualBox) to run on the Mac.

If you want to install the newer Docker for Mac, which does not require virtualbox, you can install that through Homebrew's Cask:

brew install --cask docker 
open /Applications/

curl -GET and -X GET

The use of -X [WHATEVER] merely changes the request's method string used in the HTTP request. This is easier to understand with two examples — one with -X [WHATEVER] and one without — and the associated HTTP request headers for each:

# curl -XPANTS -o nul -v
* Connected to ( port 80 (#0)
> PANTS / HTTP/1.1
> Host:
> User-Agent: curl/7.42.0
> Accept: */*

# curl -o nul -v
* Connected to ( port 80 (#0)
> GET / HTTP/1.1
> Host:
> User-Agent: curl/7.42.0
> Accept: */*

SQL Query - SUM(CASE WHEN x THEN 1 ELSE 0) for multiple columns

I would change the query in the following ways:

  1. Do the aggregation in subqueries. This can take advantage of more information about the table for optimizing the group by.
  2. Combine the second and third subqueries. They are aggregating on the same column. This requires using a left outer join to ensure that all data is available.
  3. By using count(<fieldname>) you can eliminate the comparisons to is null. This is important for the second and third calculated values.
  4. To combine the second and third queries, it needs to count an id from the mde table. These use mde.mdeid.

The following version follows your example by using union all:

SELECT CAST(Detail.ReceiptDate AS DATE) AS "Date",
       SUM(TOTALMAILED) as TotalMailed,
FROM ((select SentDate AS "ReceiptDate", COUNT(*) as TotalMailed,
       from MailDataExtract
       where SentDate is not null
       group by SentDate
      ) union all
      (select MDE.ReturnMailDate AS ReceiptDate, 0,
              COUNT(distinct mde.mdeid) as TOTALUNDELINOTICESRECEIVED,
              SUM(case when sd.ReturnMailTypeId = 1 then 1 else 0 end) as TRACEUNDELNOTICESRECEIVED
       from MailDataExtract MDE left outer join
            DTSharedData.dbo.ScanData SD
            ON SD.ScanDataID = MDE.ReturnScanDataID
       group by MDE.ReturnMailDate;
     ) detail
GROUP BY CAST(Detail.ReceiptDate AS DATE)

The following does something similar using full outer join:

SELECT coalesce(sd.ReceiptDate, mde.ReceiptDate) AS "Date",
FROM (select cast(SentDate as date) AS "ReceiptDate", COUNT(*) as TotalMailed
      from MailDataExtract
      where SentDate is not null
      group by cast(SentDate as date)
     ) sd full outer join
    (select cast(MDE.ReturnMailDate as date) AS ReceiptDate,
            COUNT(distinct mde.mdeID) as TOTALUNDELINOTICESRECEIVED,
            SUM(case when sd.ReturnMailTypeId = 1 then 1 else 0 end) as TRACEUNDELNOTICESRECEIVED
     from MailDataExtract MDE left outer join
          DTSharedData.dbo.ScanData SD
          ON SD.ScanDataID = MDE.ReturnScanDataID
     group by cast(MDE.ReturnMailDate as date)
    ) mde
    on sd.ReceiptDate = mde.ReceiptDate

How do I get the value of a registry key and ONLY the value using powershell

Not sure at what version this capability arrived, but you can use something like this to return all the properties of multiple child registry entries in an array:

$InstalledSoftware = Get-ChildItem "HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall" | ForEach-Object {Get-ItemProperty "Registry::$_"}

Only adding this as Google brought me here for a relevant reason and I eventually came up with the above one-liner for dredging the registry.

Get table column names in MySQL?

$col = $db->query("SHOW COLUMNS FROM category");

while ($fildss = $col->fetch_array())
    $filds[] = '"{'.$fildss['Field'].'}"';
    $values[] = '$rows->'.$fildss['Field'].'';

if($type == 'value')
    return $values = implode(',', $values);
else {
     return $filds = implode(',', $filds);

No space left on device

You can execute the following commands

lsof / |grep deleted

kill the process id's, which free up the disk space.

How to execute raw SQL in Flask-SQLAlchemy app

result = db.engine.execute(text("<sql here>"))

executes the <sql here> but doesn't commit it unless you're on autocommit mode. So, inserts and updates wouldn't reflect in the database.

To commit after the changes, do

result = db.engine.execute(text("<sql here>").execution_options(autocommit=True))

NoSuchMethodError in javax.persistence.Table.indexes()[Ljavax/persistence/Index

I update my Hibernate JPA to 2.1 and It works.


InputStream from a URL

(a) isn't a 'file URL'. It isn't a URL at all. If you put http:// on the front of it it would be an HTTP URL, which is clearly what you intend here.

(b) FileInputStream is for files, not URLs.

(c) The way to get an input stream from any URL is via URL.openStream(), or URL.getConnection().getInputStream(), which is equivalent but you might have other reasons to get the URLConnection and play with it first.

Eclipse internal error while initializing Java tooling

In my case, I had two of three projects with this problem in my current workspace. I opened workspace catalog and made a backup of corrupted projects, deleted them afterwards. Then opened eclipse once again. Obviously there was missing data to work with. Closed eclipse once again and added back earlier saved projects without metadata catalogs.

TL;DR. Just remove metadata catalogs from projects in your workspace.

Mixed mode assembly is built against version ‘v2.0.50727' of the runtime

If the error happens with error column "File" as SGEN, then the fix needs to be in a file sgen.exe.config, next to sgen.exe. For example, for VS 2015, create C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.6 Tools\sgen.exe.config. Minimum file contents: <configuration><startup useLegacyV2RuntimeActivationPolicy="true"/></configuration>

Source: SGEN Mixed mode assembly

What is thread Safe in java?

Thread safe simply means that it may be used from multiple threads at the same time without causing problems. This can mean that access to any resources are synchronized, or whatever.

Change background position with jQuery

rebellion's answer above won't actually work, because to CSS, 'background-position' is actually shorthand for 'background-position-x' and 'background-position-y' so the correct version of his code would be:

    $('#submenu li').hover(function(){
        $('#carousel').css('background-position-x', newValueX);
        $('#carousel').css('background-position-y', newValue);
    }, function(){
        $('#carousel').css('background-position-x', oldValueX);
        $('#carousel').css('background-position-y', oldValueY);

It took about 4 hours of banging my head against it to come to that aggravating realization.

Launch an app on OS X with command line

With applescript:

tell application "Firefox" to activate

Java regular expression OR operator

You can just use the pipe on its own:


for example:

String s = "string1, string2, string3";
System.out.println(s.replaceAll("string1|string2", "blah"));


blah, blah, string3

The main reason to use parentheses is to limit the scope of the alternatives:

String s = "string1, string2, string3";
System.out.println(s.replaceAll("string(1|2)", "blah"));

has the same output. but if you just do this:

String s = "string1, string2, string3";
System.out.println(s.replaceAll("string1|2", "blah"));

you get:

blah, stringblah, string3

because you've said "string1" or "2".

If you don't want to capture that part of the expression use ?::

String s = "string1, string2, string3";
System.out.println(s.replaceAll("string(?:1|2)", "blah"));

How to correctly implement custom iterators and const_iterators?

I'm going to show you how you can easily define iterators for your custom containers, but just in case I have created a c++11 library that allows you to easily create custom iterators with custom behavior for any type of container, contiguous or non-contiguous.

You can find it on Github

Here are the simple steps to creating and using custom iterators:

  1. Create your "custom iterator" class.
  2. Define typedefs in your "custom container" class.
    • e.g. typedef blRawIterator< Type > iterator;
    • e.g. typedef blRawIterator< const Type > const_iterator;
  3. Define "begin" and "end" functions
    • e.g. iterator begin(){return iterator(&m_data[0]);};
    • e.g. const_iterator cbegin()const{return const_iterator(&m_data[0]);};
  4. We're Done!!!

Finally, onto defining our custom iterator classes:

NOTE: When defining custom iterators, we derive from the standard iterator categories to let STL algorithms know the type of iterator we've made.

In this example, I define a random access iterator and a reverse random access iterator:

  1. //-------------------------------------------------------------------
    // Raw iterator with random access
    template<typename blDataType>
    class blRawIterator
        using iterator_category = std::random_access_iterator_tag;
        using value_type = blDataType;
        using difference_type = std::ptrdiff_t;
        using pointer = blDataType*;
        using reference = blDataType&;
        blRawIterator(blDataType* ptr = nullptr){m_ptr = ptr;}
        blRawIterator(const blRawIterator<blDataType>& rawIterator) = default;
        blRawIterator<blDataType>&                  operator=(const blRawIterator<blDataType>& rawIterator) = default;
        blRawIterator<blDataType>&                  operator=(blDataType* ptr){m_ptr = ptr;return (*this);}
        operator                                    bool()const
                return true;
                return false;
        bool                                        operator==(const blRawIterator<blDataType>& rawIterator)const{return (m_ptr == rawIterator.getConstPtr());}
        bool                                        operator!=(const blRawIterator<blDataType>& rawIterator)const{return (m_ptr != rawIterator.getConstPtr());}
        blRawIterator<blDataType>&                  operator+=(const difference_type& movement){m_ptr += movement;return (*this);}
        blRawIterator<blDataType>&                  operator-=(const difference_type& movement){m_ptr -= movement;return (*this);}
        blRawIterator<blDataType>&                  operator++(){++m_ptr;return (*this);}
        blRawIterator<blDataType>&                  operator--(){--m_ptr;return (*this);}
        blRawIterator<blDataType>                   operator++(int){auto temp(*this);++m_ptr;return temp;}
        blRawIterator<blDataType>                   operator--(int){auto temp(*this);--m_ptr;return temp;}
        blRawIterator<blDataType>                   operator+(const difference_type& movement){auto oldPtr = m_ptr;m_ptr+=movement;auto temp(*this);m_ptr = oldPtr;return temp;}
        blRawIterator<blDataType>                   operator-(const difference_type& movement){auto oldPtr = m_ptr;m_ptr-=movement;auto temp(*this);m_ptr = oldPtr;return temp;}
        difference_type                             operator-(const blRawIterator<blDataType>& rawIterator){return std::distance(rawIterator.getPtr(),this->getPtr());}
        blDataType&                                 operator*(){return *m_ptr;}
        const blDataType&                           operator*()const{return *m_ptr;}
        blDataType*                                 operator->(){return m_ptr;}
        blDataType*                                 getPtr()const{return m_ptr;}
        const blDataType*                           getConstPtr()const{return m_ptr;}
        blDataType*                                 m_ptr;
  2. //-------------------------------------------------------------------
    // Raw reverse iterator with random access
    template<typename blDataType>
    class blRawReverseIterator : public blRawIterator<blDataType>
        blRawReverseIterator(blDataType* ptr = nullptr):blRawIterator<blDataType>(ptr){}
        blRawReverseIterator(const blRawIterator<blDataType>& rawIterator){this->m_ptr = rawIterator.getPtr();}
        blRawReverseIterator(const blRawReverseIterator<blDataType>& rawReverseIterator) = default;
        blRawReverseIterator<blDataType>&           operator=(const blRawReverseIterator<blDataType>& rawReverseIterator) = default;
        blRawReverseIterator<blDataType>&           operator=(const blRawIterator<blDataType>& rawIterator){this->m_ptr = rawIterator.getPtr();return (*this);}
        blRawReverseIterator<blDataType>&           operator=(blDataType* ptr){this->setPtr(ptr);return (*this);}
        blRawReverseIterator<blDataType>&           operator+=(const difference_type& movement){this->m_ptr -= movement;return (*this);}
        blRawReverseIterator<blDataType>&           operator-=(const difference_type& movement){this->m_ptr += movement;return (*this);}
        blRawReverseIterator<blDataType>&           operator++(){--this->m_ptr;return (*this);}
        blRawReverseIterator<blDataType>&           operator--(){++this->m_ptr;return (*this);}
        blRawReverseIterator<blDataType>            operator++(int){auto temp(*this);--this->m_ptr;return temp;}
        blRawReverseIterator<blDataType>            operator--(int){auto temp(*this);++this->m_ptr;return temp;}
        blRawReverseIterator<blDataType>            operator+(const int& movement){auto oldPtr = this->m_ptr;this->m_ptr-=movement;auto temp(*this);this->m_ptr = oldPtr;return temp;}
        blRawReverseIterator<blDataType>            operator-(const int& movement){auto oldPtr = this->m_ptr;this->m_ptr+=movement;auto temp(*this);this->m_ptr = oldPtr;return temp;}
        difference_type                             operator-(const blRawReverseIterator<blDataType>& rawReverseIterator){return std::distance(this->getPtr(),rawReverseIterator.getPtr());}
        blRawIterator<blDataType>                   base(){blRawIterator<blDataType> forwardIterator(this->m_ptr); ++forwardIterator; return forwardIterator;}

Now somewhere in your custom container class:

template<typename blDataType>
class blCustomContainer
public: // The typedefs

    typedef blRawIterator<blDataType>              iterator;
    typedef blRawIterator<const blDataType>        const_iterator;

    typedef blRawReverseIterator<blDataType>       reverse_iterator;
    typedef blRawReverseIterator<const blDataType> const_reverse_iterator;


public:  // The begin/end functions

    iterator                                       begin(){return iterator(&m_data[0]);}
    iterator                                       end(){return iterator(&m_data[m_size]);}

    const_iterator                                 cbegin(){return const_iterator(&m_data[0]);}
    const_iterator                                 cend(){return const_iterator(&m_data[m_size]);}

    reverse_iterator                               rbegin(){return reverse_iterator(&m_data[m_size - 1]);}
    reverse_iterator                               rend(){return reverse_iterator(&m_data[-1]);}

    const_reverse_iterator                         crbegin(){return const_reverse_iterator(&m_data[m_size - 1]);}
    const_reverse_iterator                         crend(){return const_reverse_iterator(&m_data[-1]);}

    // This is the pointer to the
    // beginning of the data
    // This allows the container
    // to either "view" data owned
    // by other containers or to
    // own its own data
    // You would implement a "create"
    // method for owning the data
    // and a "wrap" method for viewing
    // data owned by other containers

    blDataType*                                    m_data;

How to get date representing the first day of a month?

As of SQL Server 2012 you can use the eomonth built-in function, which is intended for getting the end of the month but can also be used to get the start as so:

select dateadd(day, 1, eomonth(<date>, -1))

If you need the result as a datetime etc., just cast it:

select cast(dateadd(day, 1, eomonth(<date>, -1)) as datetime)

Best algorithm for detecting cycles in a directed graph

The way I do it is to do a Topological Sort, counting the number of vertices visited. If that number is less than the total number of vertices in the DAG, you have a cycle.

What are OLTP and OLAP. What is the difference between them?

The difference is quite simple:

OLTP (Online Transaction Processing)

OLTP is a class of information systems that facilitate and manage transaction-oriented applications. OLTP has also been used to refer to processing in which the system responds immediately to user requests. Online transaction processing applications are high throughput and insert or update-intensive in database management. Some examples of OLTP systems include order entry, retail sales, and financial transaction systems.

OLAP (Online Analytical Processing)

OLAP is part of the broader category of business intelligence, which also encompasses relational database, report writing and data mining. Typical applications of OLAP include business reporting for sales, marketing, management reporting, business process management (BPM), budgeting and forecasting, financial reporting and similar areas.

See more details OLTP and OLAP

How do I pass data between Activities in Android application?

The most convenient way to pass data between activities is by passing intents. In the first activity from where you want to send data, you should add code,

String str = "My Data"; //Data you want to send
Intent intent = new Intent(FirstActivity.this, SecondActivity.class);
intent.putExtra("name",str); //Here you will add the data into intent to pass bw activites

You should also import

import android.content.Intent;

Then in the next Acitvity(SecondActivity), you should retrieve the data from the intent using the following code.

String name = this.getIntent().getStringExtra("name");

Hexadecimal to Integer in Java

Why do you not use the java functionality for that:

If your numbers are small (smaller than yours) you could use: Integer.parseInt(hex, 16) to convert a Hex - String into an integer.

  String hex = "ff"
  int value = Integer.parseInt(hex, 16);  

For big numbers like yours, use public BigInteger(String val, int radix)

  BigInteger value = new BigInteger(hex, 16);

@See JavaDoc:

http://localhost:50070 does not work HADOOP

port 50070 changed to 9870 in 3.0.0-alpha1

In fact, lots of others ports changed too. Look:

Namenode ports: 50470 --> 9871, 50070 --> 9870, 8020 --> 9820
Secondary NN ports: 50091 --> 9869, 50090 --> 9868
Datanode ports: 50020 --> 9867, 50010 --> 9866, 50475 --> 9865, 50075 --> 9864


How to create an object property from a variable value in JavaScript?


obj = (function(attr, val){ var a = {}; a[attr]=val; return a; })('hash', 5);


attr = 'hash';
val = 5;
var obj = (obj={}, obj[attr]=val, obj);

Anything shorter?