Programs & Examples On #Artificial intelligence

Artificial intelligence (AI) is the branch of computer science and technology that studies the development of machines able to simulate aspects of human intelligence. This tag may also refer to the part of a computer game application that controls the behavior of the virtual characters with which the player may interact during the game.

What is the difference between supervised learning and unsupervised learning?

Since you ask this very basic question, it looks like it's worth specifying what Machine Learning itself is.

Machine Learning is a class of algorithms which is data-driven, i.e. unlike "normal" algorithms it is the data that "tells" what the "good answer" is. Example: a hypothetical non-machine learning algorithm for face detection in images would try to define what a face is (round skin-like-colored disk, with dark area where you expect the eyes etc). A machine learning algorithm would not have such coded definition, but would "learn-by-examples": you'll show several images of faces and not-faces and a good algorithm will eventually learn and be able to predict whether or not an unseen image is a face.

This particular example of face detection is supervised, which means that your examples must be labeled, or explicitly say which ones are faces and which ones aren't.

In an unsupervised algorithm your examples are not labeled, i.e. you don't say anything. Of course, in such a case the algorithm itself cannot "invent" what a face is, but it can try to cluster the data into different groups, e.g. it can distinguish that faces are very different from landscapes, which are very different from horses.

Since another answer mentions it (though, in an incorrect way): there are "intermediate" forms of supervision, i.e. semi-supervised and active learning. Technically, these are supervised methods in which there is some "smart" way to avoid a large number of labeled examples. In active learning, the algorithm itself decides which thing you should label (e.g. it can be pretty sure about a landscape and a horse, but it might ask you to confirm if a gorilla is indeed the picture of a face). In semi-supervised learning, there are two different algorithms which start with the labeled examples, and then "tell" each other the way they think about some large number of unlabeled data. From this "discussion" they learn.

How to compute precision, recall, accuracy and f1-score for the multiclass case with scikit learn?

I think there is a lot of confusion about which weights are used for what. I am not sure I know precisely what bothers you so I am going to cover different topics, bear with me ;).

Class weights

The weights from the class_weight parameter are used to train the classifier. They are not used in the calculation of any of the metrics you are using: with different class weights, the numbers will be different simply because the classifier is different.

Basically in every scikit-learn classifier, the class weights are used to tell your model how important a class is. That means that during the training, the classifier will make extra efforts to classify properly the classes with high weights.
How they do that is algorithm-specific. If you want details about how it works for SVC and the doc does not make sense to you, feel free to mention it.

The metrics

Once you have a classifier, you want to know how well it is performing. Here you can use the metrics you mentioned: accuracy, recall_score, f1_score...

Usually when the class distribution is unbalanced, accuracy is considered a poor choice as it gives high scores to models which just predict the most frequent class.

I will not detail all these metrics but note that, with the exception of accuracy, they are naturally applied at the class level: as you can see in this print of a classification report they are defined for each class. They rely on concepts such as true positives or false negative that require defining which class is the positive one.

             precision    recall  f1-score   support

          0       0.65      1.00      0.79        17
          1       0.57      0.75      0.65        16
          2       0.33      0.06      0.10        17
avg / total       0.52      0.60      0.51        50

The warning

F1 score:/usr/local/lib/python2.7/site-packages/sklearn/metrics/classification.py:676: DeprecationWarning: The 
default `weighted` averaging is deprecated, and from version 0.18, 
use of precision, recall or F-score with multiclass or multilabel data  
or pos_label=None will result in an exception. Please set an explicit 
value for `average`, one of (None, 'micro', 'macro', 'weighted', 
'samples'). In cross validation use, for instance, 
scoring="f1_weighted" instead of scoring="f1".

You get this warning because you are using the f1-score, recall and precision without defining how they should be computed! The question could be rephrased: from the above classification report, how do you output one global number for the f1-score? You could:

  1. Take the average of the f1-score for each class: that's the avg / total result above. It's also called macro averaging.
  2. Compute the f1-score using the global count of true positives / false negatives, etc. (you sum the number of true positives / false negatives for each class). Aka micro averaging.
  3. Compute a weighted average of the f1-score. Using 'weighted' in scikit-learn will weigh the f1-score by the support of the class: the more elements a class has, the more important the f1-score for this class in the computation.

These are 3 of the options in scikit-learn, the warning is there to say you have to pick one. So you have to specify an average argument for the score method.

Which one you choose is up to how you want to measure the performance of the classifier: for instance macro-averaging does not take class imbalance into account and the f1-score of class 1 will be just as important as the f1-score of class 5. If you use weighted averaging however you'll get more importance for the class 5.

The whole argument specification in these metrics is not super-clear in scikit-learn right now, it will get better in version 0.18 according to the docs. They are removing some non-obvious standard behavior and they are issuing warnings so that developers notice it.

Computing scores

Last thing I want to mention (feel free to skip it if you're aware of it) is that scores are only meaningful if they are computed on data that the classifier has never seen. This is extremely important as any score you get on data that was used in fitting the classifier is completely irrelevant.

Here's a way to do it using StratifiedShuffleSplit, which gives you a random splits of your data (after shuffling) that preserve the label distribution.

from sklearn.datasets import make_classification
from sklearn.cross_validation import StratifiedShuffleSplit
from sklearn.metrics import accuracy_score, f1_score, precision_score, recall_score, classification_report, confusion_matrix

# We use a utility to generate artificial classification data.
X, y = make_classification(n_samples=100, n_informative=10, n_classes=3)
sss = StratifiedShuffleSplit(y, n_iter=1, test_size=0.5, random_state=0)
for train_idx, test_idx in sss:
    X_train, X_test, y_train, y_test = X[train_idx], X[test_idx], y[train_idx], y[test_idx]
    svc.fit(X_train, y_train)
    y_pred = svc.predict(X_test)
    print(f1_score(y_test, y_pred, average="macro"))
    print(precision_score(y_test, y_pred, average="macro"))
    print(recall_score(y_test, y_pred, average="macro"))    

Hope this helps.

Best programming based games

I'm surprised that Space Chem isn't mentioned yet. Programming with symbols, but programming nevertheless.

http://spacechemthegame.com/

What is the optimal algorithm for the game 2048?

I am the author of a 2048 controller that scores better than any other program mentioned in this thread. An efficient implementation of the controller is available on github. In a separate repo there is also the code used for training the controller's state evaluation function. The training method is described in the paper.

The controller uses expectimax search with a state evaluation function learned from scratch (without human 2048 expertise) by a variant of temporal difference learning (a reinforcement learning technique). The state-value function uses an n-tuple network, which is basically a weighted linear function of patterns observed on the board. It involved more than 1 billion weights, in total.

Performance

At 1 moves/s: 609104 (100 games average)

At 10 moves/s: 589355 (300 games average)

At 3-ply (ca. 1500 moves/s): 511759 (1000 games average)

The tile statistics for 10 moves/s are as follows:

2048: 100%
4096: 100%
8192: 100%
16384: 97%
32768: 64%
32768,16384,8192,4096: 10%

(The last line means having the given tiles at the same time on the board).

For 3-ply:

2048: 100%
4096: 100%
8192: 100%
16384: 96%
32768: 54%
32768,16384,8192,4096: 8%

However, I have never observed it obtaining the 65536 tile.

source of historical stock data

Let me add a source I just discovered, found here.

It has lots of historical stock data in csv format and was gathered by Andy Pavlo, who according to his homepage is an "Assistant Professor in the Computer Science Department at Carnegie Mellon University".

What is the role of the bias in neural networks?

Other than mentioned answers..I would like to add some other points.

Bias acts as our anchor. It's a way for us to have some kind of baseline where we don't go below that. In terms of a graph, think of like y=mx+b it's like a y-intercept of this function.

output = input times the weight value and added a bias value and then apply an activation function.

What's is the difference between train, validation and test set, in neural networks?

In simple words define Training set, Test set, Validation set

Training set: Is used for finding Nearest neighbors. Validation set: Is for finding different k which is applying to train set. Test set: Is used for finding the maximum accuracy and unseen data in future.

What are good examples of genetic algorithms/genetic programming solutions?

In 2007-9 I developed some software for reading datamatrix patterns. Often these patterns were difficult to read, being indented into scratched surfaces with all kinds of reflectance properties, fuzzy chemically etched markings and so on. I used a GA to fine tune various parameters of the vision algorithms to give the best results on a database of 300 images having known properties. Parameters were things like downsampling resolution, RANSAC parameters, amount of erosion and dilation, low pass filtering radius, and a few others. Running the optimisation over several days this produced results which were about 20% better than naive values on a test set of images unseen during the optimisation phase.

This system was completely written from scratch, and I didn't use any other libraries. I'm not opposed to using such things, provided that they give a reliable result, but you have to be careful about license compatibility and code portability issues.

What algorithm for a tic-tac-toe game can I use to determine the "best move" for the AI?

What you need (for tic-tac-toe or a far more difficult game like Chess) is the minimax algorithm, or its slightly more complicated variant, alpha-beta pruning. Ordinary naive minimax will do fine for a game with as small a search space as tic-tac-toe, though.

In a nutshell, what you want to do is not to search for the move that has the best possible outcome for you, but rather for the move where the worst possible outcome is as good as possible. If you assume your opponent is playing optimally, you have to assume they will take the move that is worst for you, and therefore you have to take the move that MINimises their MAXimum gain.

How to get Tensorflow tensor dimensions (shape) as int values?

for a 2-D tensor, you can get the number of rows and columns as int32 using the following code:

rows, columns = map(lambda i: i.value, tensor.get_shape())

Epoch vs Iteration when training neural networks

Many neural network training algorithms involve making multiple presentations of the entire data set to the neural network. Often, a single presentation of the entire data set is referred to as an "epoch". In contrast, some algorithms present data to the neural network a single case at a time.

"Iteration" is a much more general term, but since you asked about it together with "epoch", I assume that your source is referring to the presentation of a single case to a neural network.

Convert DataTable to List<T>

The method ConvertToList that is posted below and uses reflection works perfectly for me. Thanks.

I made a slight modification to make it work with conversions on the T property types.

public List<T> ConvertToList<T>(DataTable dt)
{
    var columnNames = dt.Columns.Cast<DataColumn>()
            .Select(c => c.ColumnName)
            .ToList();
    var properties = typeof(T).GetProperties();
    return dt.AsEnumerable().Select(row =>
    {
        var objT = Activator.CreateInstance<T>();
        foreach (var pro in properties)
        {
            if (columnNames.Contains(pro.Name))
            {
                 PropertyInfo pI = objT.GetType().GetProperty(pro.Name);
                 pro.SetValue(objT, row[pro.Name] == DBNull.Value ? null : Convert.ChangeType(row[pro.Name], pI.PropertyType));
            }
        }
        return objT;
   }).ToList();
}

Hope it helps. Regards.

Can't update data-attribute value

Had similar problem and in the end I had to set both

obj.attr('data-myvar','myval')

and

obj.data('myvar','myval')

And after this

obj.data('myvar') == obj.attr('data-myvar')

Hope this helps.

Owl Carousel Won't Autoplay

Setting autoPlay: true didn't work for me. But on setting autoPlay: 5000 it worked.

Horizontal ListView in Android?

Download the jar file from here

now put it into your libs folder, right click it and select 'Add as library'

now in main.xml put this code

 <com.devsmart.android.ui.HorizontalListView
    android:id="@+id/hlistview"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    />

now in Activity class if you want Horizontal Listview with images then put this code

  HorizontalListView hListView = (HorizontalListView) findViewById(R.id.hlistview);
    hListView.setAdapter(new HAdapter(this));


 private class HAdapter extends BaseAdapter {

    LayoutInflater inflater;

    public HAdapter(Context context) {
        inflater = LayoutInflater.from(context);

    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return Const.template.length;
    }

    @Override
    public Object getItem(int position) {
        // TODO Auto-generated method stub
        return position;
    }

    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        HViewHolder holder;
        if (convertView == null) {
            convertView = inflater.inflate(R.layout.listinflate, null);
            holder = new HViewHolder();
            convertView.setTag(holder);

        } else {
            holder = (HViewHolder) convertView.getTag();
        }
        holder.img = (ImageView) convertView.findViewById(R.id.image);
        holder.img.setImageResource(Const.template[position]);
        return convertView;
    }

}

class HViewHolder {
    ImageView img;
}

How can I check if given int exists in array?

You almost never have to write your own loops in C++. Here, you can use std::find.

const int toFind = 42;
int* found = std::find (myArray, std::end (myArray), toFind);
if (found != std::end (myArray))
{
  std::cout << "Found.\n"
}
else
{
  std::cout << "Not found.\n";
}

std::end requires C++11. Without it, you can find the number of elements in the array with:

const size_t numElements = sizeof (myArray) / sizeof (myArray[0]);

...and the end with:

int* end = myArray + numElements;

exceeds the list view threshold 5000 items in Sharepoint 2010

I had the same problem.please do the following it may help you: By Default List View Threshold set at only 5,000 items this is because of Sharepoint server performance.

To Change the LVT:

  1. Click SharePoint Central Administration,
  2. Go to Application Management
  3. Manage Web Applications
  4. Select your application
  5. Click General Settings at the ribbon
  6. Select Resource Throttling
  7. List View Threshold limit --> change the value to your need.
  8. Also change the List View Threshold for Auditors and Administrators.if you are a administrator.

Click OK to save it.

Convert base64 string to image

To decode:

byte[] image = Base64.getDecoder().decode(base64string);

To encode:

String text = Base64.getEncoder().encodeToString(imageData);

Troubleshooting "Warning: session_start(): Cannot send session cache limiter - headers already sent"

I had a website transferring from one host to another, it seemed to work fine on the old host but a few pages on the new host threw the error

Warning: session_start(): Cannot send session cache limiter - headers already sent
while I always kept the

 <?php
session_start(); 

at the top of the page no spaces and nothing inserted before

it really bugged me that I stared every page with the session opening, and it worked on some pages and run through a bug on others I picked the pages that had the problems, backed them up, created new blank pages and simply copied and pasted the code as is, saved and uploaded and boom, problem gone!

this is something you guys may need to consider, it may have been the encoding of the page, or something, not sure the exact source of the problem, but here is a fix to look at in case you guys run into a similar problem

cheers!

npm check and update package if needed

  • To update a single local package:

    1. First find out your outdated packages:

      npm outdated

    2. Then update the package or packages that you want manually as:

      npm update --save package_name

This way it is not necessary to update your local package.json file.

Note that this will update your package to the latest version.

  • If you write some version in your package.json file and do:

    npm update package_name

    In this case you will get just the next stable version (wanted) regarding the version that you wrote in your package.json file.

And with npm list (package_name) you can find out the current version of your local packages.

Adobe Acrobat Pro make all pages the same dimension

You have to use the Print to a New PDF option using the PDF printer. Once in the dialog box, set the page scaling to 100% and set your page size. Once you do that, your new PDF will be uniform in page sizes.

Difference between "enqueue" and "dequeue"

A queue is a certain 2-sided data structure. You can add new elements on one side, and remove elements from the other side (as opposed to a stack that has only one side). Enqueue means to add an element, dequeue to remove an element. Please have a look here.

How to convert string to float?

Use atof() or strtof()* instead:

printf("float value : %4.8f\n" ,atof(s)); 
printf("float value : %4.8f\n" ,strtof(s, NULL)); 

http://www.cplusplus.com/reference/clibrary/cstdlib/atof/
http://www.cplusplus.com/reference/cstdlib/strtof/

  • atoll() is meant for integers.
  • atof()/strtof() is for floats.

The reason why you only get 4.00 with atoll() is because it stops parsing when it finds the first non-digit.

*Note that strtof() requires C99 or C++11.

Which characters are valid/invalid in a JSON key name?

It is worth mentioning that while starting the keys with numbers is valid, it could cause some unintended issues.

Example:

var testObject = {
    "1tile": "test value"
};
console.log(testObject.1tile); // fails, invalid syntax
console.log(testObject["1tile"]; // workaround

Pandas convert dataframe to array of tuples

This answer doesn't add any answers that aren't already discussed, but here are some speed results. I think this should resolve questions that came up in the comments. All of these look like they are O(n), based on these three values.

TL;DR: tuples = list(df.itertuples(index=False, name=None)) and tuples = list(zip(*[df[c].values.tolist() for c in df])) are tied for the fastest.

I did a quick speed test on results for three suggestions here:

  1. The zip answer from @pirsquared: tuples = list(zip(*[df[c].values.tolist() for c in df]))
  2. The accepted answer from @wes-mckinney: tuples = [tuple(x) for x in df.values]
  3. The itertuples answer from @ksindi with the name=None suggestion from @Axel: tuples = list(df.itertuples(index=False, name=None))
from numpy import random
import pandas as pd


def create_random_df(n):
    return pd.DataFrame({"A": random.randint(n, size=n), "B": random.randint(n, size=n)})

Small size:

df = create_random_df(10000)
%timeit tuples = list(zip(*[df[c].values.tolist() for c in df]))
%timeit tuples = [tuple(x) for x in df.values]
%timeit tuples = list(df.itertuples(index=False, name=None))

Gives:

1.66 ms ± 200 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)
15.5 ms ± 1.52 ms per loop (mean ± std. dev. of 7 runs, 100 loops each)
1.74 ms ± 75.4 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

Larger:

df = create_random_df(1000000)
%timeit tuples = list(zip(*[df[c].values.tolist() for c in df]))
%timeit tuples = [tuple(x) for x in df.values]
%timeit tuples = list(df.itertuples(index=False, name=None))

Gives:

202 ms ± 5.91 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)
1.52 s ± 98.1 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
209 ms ± 11.8 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)

As much patience as I have:

df = create_random_df(10000000)
%timeit tuples = list(zip(*[df[c].values.tolist() for c in df]))
%timeit tuples = [tuple(x) for x in df.values]
%timeit tuples = list(df.itertuples(index=False, name=None))

Gives:

1.78 s ± 118 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
15.4 s ± 222 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
1.68 s ± 96.3 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)

The zip version and the itertuples version are within the confidence intervals each other. I suspect that they are doing the same thing under the hood.

These speed tests are probably irrelevant though. Pushing the limits of my computer's memory doesn't take a huge amount of time, and you really shouldn't be doing this on a large data set. Working with those tuples after doing this will end up being really inefficient. It's unlikely to be a major bottleneck in your code, so just stick with the version you think is most readable.

MySQL limit from descending order

Let's say we have a table with a column time and you want the last 5 entries, but you want them returned to you in asc order, not desc, this is how you do it:

select * from ( select * from `table` order by `time` desc limit 5 ) t order by `time` asc

jQuery Show-Hide DIV based on Checkbox Value

`Display

$('#cbxShowHide').click(function(){ this.checked?$('#block').show(1000):$('#block').hide(1000); //time for show });`

Getting next element while cycling through a list

I've used enumeration to handle this problem.

storage = ''
for num, value in enumerate(result, start=0):
    content = value
    if 'A' == content:
        storage = result[num + 1]

I've used num as Index here, when it finds the correct value it adds up one to the current index of actual list. Which allows me to maneuver to the next index.

I hope this helps your purpose.

How to get form values in Symfony2 controller

I got it working by this:

if ($request->getMethod() == 'POST') {
    $username = $request->request->get('username');
    $password = $request->request->get('password');

    // Do something with the post data
}

You need to have the Request $request as a parameter in the function too! Hope this helps.

Tar archiving that takes input from a list of files

For me on AIX, it worked as follows:

tar -L List.txt -cvf BKP.tar

What does elementFormDefault do in XSD?

elementFormDefault="qualified" is used to control the usage of namespaces in XML instance documents (.xml file), rather than namespaces in the schema document itself (.xsd file).

By specifying elementFormDefault="qualified" we enforce namespace declaration to be used in documents validated with this schema.

It is common practice to specify this value to declare that the elements should be qualified rather than unqualified. However, since attributeFormDefault="unqualified" is the default value, it doesn't need to be specified in the schema document, if one does not want to qualify the namespaces.

Graph implementation C++

Below is a implementation of Graph Data Structure in C++ as Adjacency List.

I have used STL vector for representation of vertices and STL pair for denoting edge and destination vertex.

#include <iostream>
#include <vector>
#include <map>
#include <string>

using namespace std;

struct vertex {
    typedef pair<int, vertex*> ve;
    vector<ve> adj; //cost of edge, destination vertex
    string name;
    vertex(string s) : name(s) {}
};

class graph
{
public:
    typedef map<string, vertex *> vmap;
    vmap work;
    void addvertex(const string&);
    void addedge(const string& from, const string& to, double cost);
};

void graph::addvertex(const string &name)
{
    vmap::iterator itr = work.find(name);
    if (itr == work.end())
    {
        vertex *v;
        v = new vertex(name);
        work[name] = v;
        return;
    }
    cout << "\nVertex already exists!";
}

void graph::addedge(const string& from, const string& to, double cost)
{
    vertex *f = (work.find(from)->second);
    vertex *t = (work.find(to)->second);
    pair<int, vertex *> edge = make_pair(cost, t);
    f->adj.push_back(edge);
}

jQuery delete confirmation box

I used this:

<a href="url/to/delete.asp" onclick="return confirm(' you want to delete?');">Delete</a>

How to replace comma with a dot in the number (or any replacement)

After replacing the character, you need to be asign to the variable.

var tt = "88,9827";
tt = tt.replace(/,/g, '.')
alert(tt)

In the alert box it will shows 88.9827

Java SE 6 vs. JRE 1.6 vs. JDK 1.6 - What do these mean?

When you type "java -version", you see three version numbers - the java version (on mine, that's "1.6.0_07"), the Java SE Runtime Environment version ("build 1.6.0_07-b06"), and the HotSpot version (on mine, that's "build 10.0-b23, mixed mode"). I suspect the "11.0" you are seeing is the HotSpot version.

Update: HotSpot is (or used to be, now they seem to use it to mean the whole VM) the just-in-time compiler that is built in to the Java Virtual Machine. God only knows why Sun gives it a separate version number.

Android Facebook style slide

As a part of my Android Common Library (ACL) I implemented own SideBar. Main advantages:

  1. Side bar can be set to any position: left, top, bottom, right
  2. Both main view and sliding view are clickable
  3. Side bar can be partially shown
  4. Stylable attributes for SideBar make easier to change it's style
  5. Artifact in maven repo
  6. Part of a big library

Source code: https://github.com/serso/android-common/tree/master/views/src/main/java/org/solovyev/android/view/sidebar

Usage: https://github.com/serso/android-common/blob/master/samples/res/layout/acl_view_layout.xml

strcpy() error in Visual studio 2012

I had to use strcpy_s and it worked.

#include "stdafx.h"
#include<iostream>
#include<string>

using namespace std;

struct student
{
    char name[30];
    int age;
};

int main()
{

    struct student s1;
    char myname[30] = "John";
    strcpy_s (s1.name, strlen(myname) + 1 ,myname );
    s1.age = 21;

    cout << " Name: " << s1.name << " age: " << s1.age << endl;
    return 0;
}

Submit button doesn't work

I faced this problem today, and the issue was I was preventing event default action in document onclick:

document.onclick = function(e) {
    e.preventDefault();
}

Document onclick usually is used for event delegation but it's wrong to prevent default for every event, you must do it only for required elements:

document.onclick = function(e) {
    if (e.target instanceof HTMLAnchorElement) e.preventDefault();
}

Java: getMinutes and getHours

While I wouldn't recommend doing so, I think it's worth pointing out that although many methods on java.util.Date have been deprecated, they do still work. In trivial situations, it may be OK to use them. Also, java.util.Calendar is pretty slow, so getMonth and getYear on Date might be be usefully quicker.

How to transfer paid android apps from one google account to another google account

It's totally feasible now. Google now allow you to transfer Android apps between accounts. Please take a look at this link: https://support.google.com/googleplay/android-developer/checklist/3294213?hl=en

JSON date to Java date?

That DateTime format is actually ISO 8601 DateTime. JSON does not specify any particular format for dates/times. If you Google a bit, you will find plenty of implementations to parse it in Java.

Here's one

If you are open to using something other than Java's built-in Date/Time/Calendar classes, I would also suggest Joda Time. They offer (among many things) a ISODateTimeFormat to parse these kinds of strings.

Xcode 4 - build output directory

From the Xcode menu on top, click preferences, select the locations tab, look at the build location option.

You have 2 options:

  1. Place build products in derived data location (recommended)
  2. Place build products in locations specified by targets

Update: On xcode 4.6.2 you need to click the advanced button on the right side below the derived data text field. Build Location select legacy.

@Directive vs @Component in Angular

A component is a directive-with-a-template and the @Component decorator is actually a @Directive decorator extended with template-oriented features.

nodejs mysql Error: Connection lost The server closed the connection

Try to use this code to handle server disconnect:

var db_config = {
  host: 'localhost',
    user: 'root',
    password: '',
    database: 'example'
};

var connection;

function handleDisconnect() {
  connection = mysql.createConnection(db_config); // Recreate the connection, since
                                                  // the old one cannot be reused.

  connection.connect(function(err) {              // The server is either down
    if(err) {                                     // or restarting (takes a while sometimes).
      console.log('error when connecting to db:', err);
      setTimeout(handleDisconnect, 2000); // We introduce a delay before attempting to reconnect,
    }                                     // to avoid a hot loop, and to allow our node script to
  });                                     // process asynchronous requests in the meantime.
                                          // If you're also serving http, display a 503 error.
  connection.on('error', function(err) {
    console.log('db error', err);
    if(err.code === 'PROTOCOL_CONNECTION_LOST') { // Connection to the MySQL server is usually
      handleDisconnect();                         // lost due to either server restart, or a
    } else {                                      // connnection idle timeout (the wait_timeout
      throw err;                                  // server variable configures this)
    }
  });
}

handleDisconnect();

In your code i am missing the parts after connection = mysql.createConnection(db_config);

How to iterate over arguments in a Bash script

Rewrite of a now-deleted answer by VonC.

Robert Gamble's succinct answer deals directly with the question. This one amplifies on some issues with filenames containing spaces.

See also: ${1:+"$@"} in /bin/sh

Basic thesis: "$@" is correct, and $* (unquoted) is almost always wrong. This is because "$@" works fine when arguments contain spaces, and works the same as $* when they don't. In some circumstances, "$*" is OK too, but "$@" usually (but not always) works in the same places. Unquoted, $@ and $* are equivalent (and almost always wrong).

So, what is the difference between $*, $@, "$*", and "$@"? They are all related to 'all the arguments to the shell', but they do different things. When unquoted, $* and $@ do the same thing. They treat each 'word' (sequence of non-whitespace) as a separate argument. The quoted forms are quite different, though: "$*" treats the argument list as a single space-separated string, whereas "$@" treats the arguments almost exactly as they were when specified on the command line. "$@" expands to nothing at all when there are no positional arguments; "$*" expands to an empty string — and yes, there's a difference, though it can be hard to perceive it. See more information below, after the introduction of the (non-standard) command al.

Secondary thesis: if you need to process arguments with spaces and then pass them on to other commands, then you sometimes need non-standard tools to assist. (Or you should use arrays, carefully: "${array[@]}" behaves analogously to "$@".)

Example:

    $ mkdir "my dir" anotherdir
    $ ls
    anotherdir      my dir
    $ cp /dev/null "my dir/my file"
    $ cp /dev/null "anotherdir/myfile"
    $ ls -Fltr
    total 0
    drwxr-xr-x   3 jleffler  staff  102 Nov  1 14:55 my dir/
    drwxr-xr-x   3 jleffler  staff  102 Nov  1 14:55 anotherdir/
    $ ls -Fltr *
    my dir:
    total 0
    -rw-r--r--   1 jleffler  staff  0 Nov  1 14:55 my file

    anotherdir:
    total 0
    -rw-r--r--   1 jleffler  staff  0 Nov  1 14:55 myfile
    $ ls -Fltr "./my dir" "./anotherdir"
    ./my dir:
    total 0
    -rw-r--r--   1 jleffler  staff  0 Nov  1 14:55 my file

    ./anotherdir:
    total 0
    -rw-r--r--   1 jleffler  staff  0 Nov  1 14:55 myfile
    $ var='"./my dir" "./anotherdir"' && echo $var
    "./my dir" "./anotherdir"
    $ ls -Fltr $var
    ls: "./anotherdir": No such file or directory
    ls: "./my: No such file or directory
    ls: dir": No such file or directory
    $

Why doesn't that work? It doesn't work because the shell processes quotes before it expands variables. So, to get the shell to pay attention to the quotes embedded in $var, you have to use eval:

    $ eval ls -Fltr $var
    ./my dir:
    total 0
    -rw-r--r--   1 jleffler  staff  0 Nov  1 14:55 my file

    ./anotherdir:
    total 0
    -rw-r--r--   1 jleffler  staff  0 Nov  1 14:55 myfile
    $ 

This gets really tricky when you have file names such as "He said, "Don't do this!"" (with quotes and double quotes and spaces).

    $ cp /dev/null "He said, \"Don't do this!\""
    $ ls
    He said, "Don't do this!"       anotherdir                      my dir
    $ ls -l
    total 0
    -rw-r--r--   1 jleffler  staff    0 Nov  1 15:54 He said, "Don't do this!"
    drwxr-xr-x   3 jleffler  staff  102 Nov  1 14:55 anotherdir
    drwxr-xr-x   3 jleffler  staff  102 Nov  1 14:55 my dir
    $ 

The shells (all of them) do not make it particularly easy to handle such stuff, so (funnily enough) many Unix programs do not do a good job of handling them. On Unix, a filename (single component) can contain any characters except slash and NUL '\0'. However, the shells strongly encourage no spaces or newlines or tabs anywhere in a path names. It is also why standard Unix file names do not contain spaces, etc.

When dealing with file names that may contain spaces and other troublesome characters, you have to be extremely careful, and I found long ago that I needed a program that is not standard on Unix. I call it escape (version 1.1 was dated 1989-08-23T16:01:45Z).

Here is an example of escape in use - with the SCCS control system. It is a cover script that does both a delta (think check-in) and a get (think check-out). Various arguments, especially -y (the reason why you made the change) would contain blanks and newlines. Note that the script dates from 1992, so it uses back-ticks instead of $(cmd ...) notation and does not use #!/bin/sh on the first line.

:   "@(#)$Id: delget.sh,v 1.8 1992/12/29 10:46:21 jl Exp $"
#
#   Delta and get files
#   Uses escape to allow for all weird combinations of quotes in arguments

case `basename $0 .sh` in
deledit)    eflag="-e";;
esac

sflag="-s"
for arg in "$@"
do
    case "$arg" in
    -r*)    gargs="$gargs `escape \"$arg\"`"
            dargs="$dargs `escape \"$arg\"`"
            ;;
    -e)     gargs="$gargs `escape \"$arg\"`"
            sflag=""
            eflag=""
            ;;
    -*)     dargs="$dargs `escape \"$arg\"`"
            ;;
    *)      gargs="$gargs `escape \"$arg\"`"
            dargs="$dargs `escape \"$arg\"`"
            ;;
    esac
done

eval delta "$dargs" && eval get $eflag $sflag "$gargs"

(I would probably not use escape quite so thoroughly these days - it is not needed with the -e argument, for example - but overall, this is one of my simpler scripts using escape.)

The escape program simply outputs its arguments, rather like echo does, but it ensures that the arguments are protected for use with eval (one level of eval; I do have a program which did remote shell execution, and that needed to escape the output of escape).

    $ escape $var
    '"./my' 'dir"' '"./anotherdir"'
    $ escape "$var"
    '"./my dir" "./anotherdir"'
    $ escape x y z
    x y z
    $ 

I have another program called al that lists its arguments one per line (and it is even more ancient: version 1.1 dated 1987-01-27T14:35:49). It is most useful when debugging scripts, as it can be plugged into a command line to see what arguments are actually passed to the command.

    $ echo "$var"
    "./my dir" "./anotherdir"
    $ al $var
    "./my
    dir"
    "./anotherdir"
    $ al "$var"
    "./my dir" "./anotherdir"
    $

[Added: And now to show the difference between the various "$@" notations, here is one more example:

$ cat xx.sh
set -x
al $@
al $*
al "$*"
al "$@"
$ sh xx.sh     *      */*
+ al He said, '"Don'\''t' do 'this!"' anotherdir my dir xx.sh anotherdir/myfile my dir/my file
He
said,
"Don't
do
this!"
anotherdir
my
dir
xx.sh
anotherdir/myfile
my
dir/my
file
+ al He said, '"Don'\''t' do 'this!"' anotherdir my dir xx.sh anotherdir/myfile my dir/my file
He
said,
"Don't
do
this!"
anotherdir
my
dir
xx.sh
anotherdir/myfile
my
dir/my
file
+ al 'He said, "Don'\''t do this!" anotherdir my dir xx.sh anotherdir/myfile my dir/my file'
He said, "Don't do this!" anotherdir my dir xx.sh anotherdir/myfile my dir/my file
+ al 'He said, "Don'\''t do this!"' anotherdir 'my dir' xx.sh anotherdir/myfile 'my dir/my file'
He said, "Don't do this!"
anotherdir
my dir
xx.sh
anotherdir/myfile
my dir/my file
$

Notice that nothing preserves the original blanks between the * and */* on the command line. Also, note that you can change the 'command line arguments' in the shell by using:

set -- -new -opt and "arg with space"

This sets 4 options, '-new', '-opt', 'and', and 'arg with space'.
]

Hmm, that's quite a long answer - perhaps exegesis is the better term. Source code for escape available on request (email to firstname dot lastname at gmail dot com). The source code for al is incredibly simple:

#include <stdio.h>
int main(int argc, char **argv)
{
    while (*++argv != 0)
        puts(*argv);
    return(0);
}

That's all. It is equivalent to the test.sh script that Robert Gamble showed, and could be written as a shell function (but shell functions didn't exist in the local version of Bourne shell when I first wrote al).

Also note that you can write al as a simple shell script:

[ $# != 0 ] && printf "%s\n" "$@"

The conditional is needed so that it produces no output when passed no arguments. The printf command will produce a blank line with only the format string argument, but the C program produces nothing.

Converting pfx to pem using openssl

You can use the OpenSSL Command line tool. The following commands should do the trick

openssl pkcs12 -in client_ssl.pfx -out client_ssl.pem -clcerts

openssl pkcs12 -in client_ssl.pfx -out root.pem -cacerts

If you want your file to be password protected etc, then there are additional options.

You can read the entire documentation here.

Speed up rsync with Simultaneous/Concurrent File Transfers?

Have you tried using rclone.org?

With rclone you could do something like

rclone copy "${source}/${subfolder}/" "${target}/${subfolder}/" --progress --multi-thread-streams=N

where --multi-thread-streams=N represents the number of threads you wish to spawn.

What is http multipart request?

I have found an excellent and relatively short explanation here.

A multipart request is a REST request containing several packed REST requests inside its entity.

SSIS Excel Connection Manager failed to Connect to the Source

My answer is very similar to the one from @biscoop, but I am going to elaborate a bit as it may apply to the question or to other people.

I had a .xls that was an extraction from one of our webapps. The Excel connection would not work (error message: "no tables or views could be loaded"). As a side note, when opening the file, there would be a warning stating that the file was from an online source and that the content needed activation.

I tried to save the same file as an .xlsx and it worked. I tried to save the same file with another name as an .xls and it worked too. So as a last test I only opened the source .xls file, clicking save and the connection worked.

Short answer: just try and see if opening the file and saving does the trick.

MySQL: When is Flush Privileges in MySQL really needed?

TL;DR

You should use FLUSH PRIVILEGES; only if you modify the grant tables directly using statements such as INSERT, UPDATE, or DELETE.

How to create an empty array in Swift?

As per Swift 5

    // An array of 'Int' elements
    let oddNumbers = [1, 3, 5, 7, 9, 11, 13, 15]

    // An array of 'String' elements
    let streets = ["Albemarle", "Brandywine", "Chesapeake"]

    // Shortened forms are preferred
    var emptyDoubles: [Double] = []

    // The full type name is also allowed
    var emptyFloats: Array<Float> = Array()

Change bootstrap navbar background color and font color

No need for the specificity .navbar-default in your CSS. Background color requires background-color:#cc333333 (or just background:#cc3333). Finally, probably best to consolidate all your customizations into a single class, as below:

.navbar-custom {
    color: #FFFFFF;
    background-color: #CC3333;
}

..

<div id="menu" class="navbar navbar-default navbar-custom">

Example: http://www.bootply.com/OusJAAvFqR#

How to uncompress a tar.gz in another directory

You can use the option -C (or --directory if you prefer long options) to give the target directory of your choice in case you are using the Gnu version of tar. The directory should exist:

mkdir foo
tar -xzf bar.tar.gz -C foo

If you are not using a tar capable of extracting to a specific directory, you can simply cd into your target directory prior to calling tar; then you will have to give a complete path to your archive, of course. You can do this in a scoping subshell to avoid influencing the surrounding script:

mkdir foo
(cd foo; tar -xzf ../bar.tar.gz)  # instead of ../ you can use an absolute path as well

Or, if neither an absolute path nor a relative path to the archive file is suitable, you also can use this to name the archive outside of the scoping subshell:

TARGET_PATH=a/very/complex/path/which/might/even/be/absolute
mkdir -p "$TARGET_PATH"
(cd "$TARGET_PATH"; tar -xzf -) < bar.tar.gz

How to use WPF Background Worker

using System;  
using System.ComponentModel;   
using System.Threading;    
namespace BackGroundWorkerExample  
{   
    class Program  
    {  
        private static BackgroundWorker backgroundWorker;  

        static void Main(string[] args)  
        {  
            backgroundWorker = new BackgroundWorker  
            {  
                WorkerReportsProgress = true,  
                WorkerSupportsCancellation = true  
            };  

            backgroundWorker.DoWork += backgroundWorker_DoWork;  
            //For the display of operation progress to UI.    
            backgroundWorker.ProgressChanged += backgroundWorker_ProgressChanged;  
            //After the completation of operation.    
            backgroundWorker.RunWorkerCompleted += backgroundWorker_RunWorkerCompleted;  
            backgroundWorker.RunWorkerAsync("Press Enter in the next 5 seconds to Cancel operation:");  

            Console.ReadLine();  

            if (backgroundWorker.IsBusy)  
            { 
                backgroundWorker.CancelAsync();  
                Console.ReadLine();  
            }  
        }  

        static void backgroundWorker_DoWork(object sender, DoWorkEventArgs e)  
        {  
            for (int i = 0; i < 200; i++)  
            {  
                if (backgroundWorker.CancellationPending)  
                {  
                    e.Cancel = true;  
                    return;  
                }  

                backgroundWorker.ReportProgress(i);  
                Thread.Sleep(1000);  
                e.Result = 1000;  
            }  
        }  

        static void backgroundWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)  
        {  
            Console.WriteLine("Completed" + e.ProgressPercentage + "%");  
        }  

        static void backgroundWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)  
        {  

            if (e.Cancelled)  
            {  
                Console.WriteLine("Operation Cancelled");  
            }  
            else if (e.Error != null)  
            {  
                Console.WriteLine("Error in Process :" + e.Error);  
            }  
            else  
            {  
                Console.WriteLine("Operation Completed :" + e.Result);  
            }  
        }  
    }  
} 

Also, referr the below link you will understand the concepts of Background:

http://www.c-sharpcorner.com/UploadFile/1c8574/threads-in-wpf/

How do you test your Request.QueryString[] variables?

Use int.TryParse instead to get rid of the try-catch block:

if (!int.TryParse(Request.QueryString["id"], out id))
{
  // error case
}

Add column to dataframe with constant value

Summing up what the others have suggested, and adding a third way

You can:

where the argument loc ( 0 <= loc <= len(columns) ) allows you to insert the column where you want.

'loc' gives you the index that your column will be at after the insertion. For example, the code above inserts the column Name as the 0-th column, i.e. it will be inserted before the first column, becoming the new first column. (Indexing starts from 0).

All these methods allow you to add a new column from a Series as well (just substitute the 'abc' default argument above with the series).

strdup() - what does it do in C?

The strdup() function is a shorthand for string duplicate, it takes in a parameter as a string constant or a string literal and allocates just enough space for the string and writes the corresponding characters in the space allocated and finally returns the address of the allocated space to the calling routine.

How to pass parameter to click event in Jquery

You don't need to pass the parameter, you can get it using .attr() method

$(function(){
    $('elements-to-match').click(function(){
        alert("The id is "+ $(this).attr("id") );
    });
});

Sharing link on WhatsApp from mobile website (not application) for Android

use it like "whatsapp://send?text=" + encodeURIComponent(your text goes here), it will definitely work.

ASP.NET Web API session or something?

in Global.asax add

public override void Init()
{
    this.PostAuthenticateRequest += MvcApplication_PostAuthenticateRequest;
    base.Init();
}

void MvcApplication_PostAuthenticateRequest(object sender, EventArgs e)
{
    System.Web.HttpContext.Current.SetSessionStateBehavior(
        SessionStateBehavior.Required);
}

give it a shot ;)

What's a good hex editor/viewer for the Mac?

I have recently started using 0xED, and like it a lot.

How to pass parameters using ui-sref in ui-router to controller

You don't necessarily need to have the parameters inside the URL.

For instance, with:

$stateProvider
.state('home', {
  url: '/',
  views: {
    '': {
      templateUrl: 'home.html',
      controller: 'MainRootCtrl'

    },
  },
  params: {
    foo: null,
    bar: null
  }
})

You will be able to send parameters to the state, using either:

$state.go('home', {foo: true, bar: 1});
// or
<a ui-sref="home({foo: true, bar: 1})">Go!</a>

Of course, if you reload the page once on the home state, you will loose the state parameters, as they are not stored anywhere.

A full description of this behavior is documented here, under the params row in the state(name, stateConfig) section.

PHP Get name of current directory

getcwd();

or

dirname(__FILE__);

or (PHP5)

basename(__DIR__) 

http://php.net/manual/en/function.getcwd.php

http://php.net/manual/en/function.dirname.php

You can use basename() to get the trailing part of the path :)

In your case, I'd say you are most likely looking to use getcwd(), dirname(__FILE__) is more useful when you have a file that needs to include another library and is included in another library.

Eg:

main.php
libs/common.php
libs/images/editor.php

In your common.php you need to use functions in editor.php, so you use

common.php:

require_once dirname(__FILE__) . '/images/editor.php';

main.php:

require_once libs/common.php

That way when common.php is require'd in main.php, the call of require_once in common.php will correctly includes editor.php in images/editor.php instead of trying to look in current directory where main.php is run.

Linking a UNC / Network drive on an html page

To link to a UNC path from an HTML document, use file:///// (yes, that's five slashes).

file://///server/path/to/file.txt

Note that this is most useful in IE and Outlook/Word. It won't work in Chrome or Firefox, intentionally - the link will fail silently. Some words from the Mozilla team:

For security purposes, Mozilla applications block links to local files (and directories) from remote files.

And less directly, from Google:

Firefox and Chrome doesn't open "file://" links from pages that originated from outside the local machine. This is a design decision made by those browsers to improve security.

The Mozilla article includes a set of client settings you can use to override this behavior in Firefox, and there are extensions for both browsers to override this restriction.

'adb' is not recognized as an internal or external command, operable program or batch file

On Window, sometimes I feel hard to click through many steps to find platform-tools and open Environment Variables Prompt, so the below steps maybe help

Step 1. Open cmd as Administrator

Step 2. File platform-tools path

cd C:\
dir /s adb.exe

Step 3: Edit Path in Edit Enviroment Variables Prompt

rundll32 sysdm.cpl,EditEnvironmentVariables

more, the command to open environment variables can not remember, so I often make an alias for it (eg: editenv), if you need to work with environment variables multiple time, you can use a permanent doskey to make alias

Step 4: Restart cmd

Add views in UIStackView programmatically

    //Image View
    let imageView               = UIImageView()
    imageView.backgroundColor   = UIColor.blueColor()
    imageView.heightAnchor.constraintEqualToConstant(120.0).active = true
    imageView.widthAnchor.constraintEqualToConstant(120.0).active = true
    imageView.image = UIImage(named: "buttonFollowCheckGreen")

    //Text Label
    let textLabel               = UILabel()
    textLabel.backgroundColor   = UIColor.greenColor()
    textLabel.widthAnchor.constraintEqualToConstant(self.view.frame.width).active = true
    textLabel.heightAnchor.constraintEqualToConstant(20.0).active = true
    textLabel.text  = "Hi World"
    textLabel.textAlignment = .Center


    //Third View
    let thirdView               = UIImageView()
    thirdView.backgroundColor   = UIColor.magentaColor()
    thirdView.heightAnchor.constraintEqualToConstant(120.0).active = true
    thirdView.widthAnchor.constraintEqualToConstant(120.0).active = true
    thirdView.image = UIImage(named: "buttonFollowMagenta")


    //Stack View
    let stackView   = UIStackView()
    stackView.axis  = UILayoutConstraintAxis.Vertical
    stackView.distribution  = UIStackViewDistribution.EqualSpacing
    stackView.alignment = UIStackViewAlignment.Center
    stackView.spacing   = 16.0

    stackView.addArrangedSubview(imageView)
    stackView.addArrangedSubview(textLabel)
    stackView.addArrangedSubview(thirdView)
    stackView.translatesAutoresizingMaskIntoConstraints = false;

    self.view.addSubview(stackView)

    //Constraints
    stackView.centerXAnchor.constraintEqualToAnchor(self.view.centerXAnchor).active = true
    stackView.centerYAnchor.constraintEqualToAnchor(self.view.centerYAnchor).active = true

Improved on the answer by @Oleg Popov

ClientScript.RegisterClientScriptBlock?

See if the below helps you:

I was using the following earlier:

ClientScript.RegisterClientScriptBlock(Page.GetType(), "AlertMsg", "<script language='javascript'>alert('The Web Policy need to be accepted to submit the new assessor information.');</script>");

After implementing AJAX in this page, it stopped working. After reading your blog, I changed the above to:

ScriptManager.RegisterClientScriptBlock(imgBtnSubmit, this.GetType(), "AlertMsg", "<script language='javascript'>alert('The Web Policy need to be accepted to submit the new assessor information.');</script>", false);

This is working perfectly fine.

(It’s .NET 2.0 Framework, I am using)

How can I make robocopy silent in the command line except for progress?

A workaround, if you want it to be absolutely silent, is to redirect the output to a file (and optionally delete it later).

Robocopy src dest > output.log
del output.log

Is it possible to have empty RequestParam values use the defaultValue?

You can keep primitive type by setting default value, in the your case just add "required = false" property:

@RequestParam(value = "i", required = false, defaultValue = "10") int i

P.S. This page from Spring documentation might be useful: Annotation Type RequestParam

Easiest way to copy a table from one database to another?

If your tables are on the same mysql server you can run the following

CREATE TABLE destination_db.my_table SELECT * FROM source_db.my_table;
ALTER TABLE destination_db.my_table ADD PRIMARY KEY (id); 
ALTER TABLE destination_db.my_table MODIFY COLUMN id INT AUTO_INCREMENT;

String.Format like functionality in T-SQL?

take a look at xp_sprintf. example below.

DECLARE @ret_string varchar (255)
EXEC xp_sprintf @ret_string OUTPUT, 
    'INSERT INTO %s VALUES (%s, %s)', 'table1', '1', '2'
PRINT @ret_string

Result looks like this:

INSERT INTO table1 VALUES (1, 2)

Just found an issue with the max size (255 char limit) of the string with this so there is an alternative function you can use:

create function dbo.fnSprintf (@s varchar(MAX), 
                @params varchar(MAX), @separator char(1) = ',')
returns varchar(MAX)
as
begin
declare @p varchar(MAX)
declare @paramlen int

set @params = @params + @separator
set @paramlen = len(@params)
while not @params = ''
begin
    set @p = left(@params+@separator, charindex(@separator, @params)-1)
    set @s = STUFF(@s, charindex('%s', @s), 2, @p)
    set @params = substring(@params, len(@p)+2, @paramlen)
end
return @s
end

To get the same result as above you call the function as follows:

print dbo.fnSprintf('INSERT INTO %s VALUES (%s, %s)', 'table1,1,2', default)

How to delete and update a record in Hive

Yes, rightly said. Hive does not support UPDATE option. But the following alternative could be used to achieve the result:

Update records in a partitioned Hive table:

  1. The main table is assumed to be partitioned by some key.
  2. Load the incremental data (the data to be updated) to a staging table partitioned with the same keys as the main table.
  3. Join the two tables (main & staging tables) using a LEFT OUTER JOIN operation as below:

    insert overwrite table main_table partition (c,d) select t2.a, t2.b, t2.c,t2.d from staging_table t2 left outer join main_table t1 on t1.a=t2.a;

In the above example, the main_table & the staging_table are partitioned using the (c,d) keys. The tables are joined via a LEFT OUTER JOIN and the result is used to OVERWRITE the partitions in the main_table.

A similar approach could be used in the case of un-partitioned Hive table UPDATE operations too.

Check if a varchar is a number (TSQL)

Using SQL Server 2012+, you can use the TRY_* functions if you have specific needs. For example,

-- will fail for decimal values, but allow negative values
TRY_CAST(@value AS INT) IS NOT NULL 

-- will fail for non-positive integers; can be used with other examples below as well, or reversed if only negative desired
TRY_CAST(@value AS INT) > 0

-- will fail if a $ is used, but allow decimals to the specified precision
TRY_CAST(@value AS DECIMAL(10,2)) IS NOT NULL 

-- will allow valid currency
TRY_CAST(@value AS MONEY) IS NOT NULL  

-- will allow scientific notation to be used like 1.7E+3
TRY_CAST(@value AS FLOAT) IS NOT NULL 

MySQL: #126 - Incorrect key file for table

mysqlcheck -r -f  -uroot -p   --use_frm db_name

will normally do the trick

How do I pass environment variables to Docker containers?

You can pass using -e parameters with docker run .. command as mentioned here and as mentioned by @errata.

However, the possible downside of this approach is that your credentials will be displayed in the process listing, where you run it.

To make it more secure, you may write your credentials in a configuration file and do docker run with --env-file as mentioned here. Then you can control the access of that config file so that others having access to that machine wouldn't see your credentials.

How to disable compiler optimizations in gcc?

You can disable optimizations if you pass -O0 with the gcc command-line.

E.g. to turn a .C file into a .S file call:

gcc -O0 -S test.c

Thread-safe List<T> property

Here is the class for thread safe list without lock

 public class ConcurrentList   
    {
        private long _i = 1;
        private ConcurrentDictionary<long, T> dict = new ConcurrentDictionary<long, T>();  
        public int Count()
        {
            return dict.Count;
        }
         public List<T> ToList()
         {
            return dict.Values.ToList();
         }

        public T this[int i]
        {
            get
            {
                long ii = dict.Keys.ToArray()[i];
                return dict[ii];
            }
        }
        public void Remove(T item)
        {
            T ov;
            var dicItem = dict.Where(c => c.Value.Equals(item)).FirstOrDefault();
            if (dicItem.Key > 0)
            {
                dict.TryRemove(dicItem.Key, out ov);
            }
            this.CheckReset();
        }
        public void RemoveAt(int i)
        {
            long v = dict.Keys.ToArray()[i];
            T ov;
            dict.TryRemove(v, out ov);
            this.CheckReset();
        }
        public void Add(T item)
        {
            dict.TryAdd(_i, item);
            _i++;
        }
        public IEnumerable<T> Where(Func<T, bool> p)
        {
            return dict.Values.Where(p);
        }
        public T FirstOrDefault(Func<T, bool> p)
        {
            return dict.Values.Where(p).FirstOrDefault();
        }
        public bool Any(Func<T, bool> p)
        {
            return dict.Values.Where(p).Count() > 0 ? true : false;
        }
        public void Clear()
        {
            dict.Clear();
        }
        private void CheckReset()
        {
            if (dict.Count == 0)
            {
                this.Reset();
            }
        }
        private void Reset()
        {
            _i = 1;
        }
    }

How to link home brew python version and set it as default

You can follow these steps.

$ python3 --version  
$ brew unlink python@2
$ brew link python3   
$ python3 --version   

All steps

How can I set a custom date time format in Oracle SQL Developer?

You can change this in preferences:

  1. From Oracle SQL Developer's menu go to: Tools > Preferences.
  2. From the Preferences dialog, select Database > NLS from the left panel.
  3. From the list of NLS parameters, enter DD-MON-RR HH24:MI:SS into the Date Format field.
  4. Save and close the dialog, done!

Here is a screenshot:

Changing Date Format preferences in Oracle SQL Developer

Simplest way to display current month and year like "Aug 2016" in PHP?

Here is a simple and more update format of getting the data:

   $now = new \DateTime('now');
   $month = $now->format('m');
   $year = $now->format('Y');

What is the difference between supervised learning and unsupervised learning?

Supervised learning

You have input x and a target output t. So you train the algorithm to generalize to the missing parts. It is supervised because the target is given. You are the supervisor telling the algorithm: For the example x, you should output t!

Unsupervised learning

Although segmentation, clustering and compression are usually counted in this direction, I have a hard time to come up with a good definition for it.

Let's take auto-encoders for compression as an example. While you only have the input x given, it is the human engineer how tells the algorithm that the target is also x. So in some sense, this is not different from supervised learning.

And for clustering and segmentation, I'm not too sure if it really fits the definition of machine learning (see other question).

appending array to FormData and send via AJAX

This is an old question but I ran into this problem with posting objects along with files recently. I needed to be able to post an object, with child properties that were objects and arrays as well.

The function below will walk through an object and create the correct formData object.

// formData - instance of FormData object
// data - object to post
function getFormData(formData, data, previousKey) {
  if (data instanceof Object) {
    Object.keys(data).forEach(key => {
      const value = data[key];
      if (value instanceof Object && !Array.isArray(value)) {
        return this.getFormData(formData, value, key);
      }
      if (previousKey) {
        key = `${previousKey}[${key}]`;
      }
      if (Array.isArray(value)) {
        value.forEach(val => {
          formData.append(`${key}[]`, val);
        });
      } else {
        formData.append(key, value);
      }
    });
  }
}

This will convert the following json -

{
  name: 'starwars',
  year: 1977,
  characters: {
    good: ['luke', 'leia'],
    bad: ['vader'],
  },
}

into the following FormData

 name, starwars
 year, 1977
 characters[good][], luke
 characters[good][], leia
 characters[bad][], vader

Can not run Java Applets in Internet Explorer 11 using JRE 7u51

Once Java(tm) Plug -In 2 SSV Helper was incompatible
Above solution did not work for me.
I solved it with the below instruction.
1. Go to IE settings
2. Internet options
3. Select Advanced tab
4. Scroll down to Security
5. Uncheck “Enable Enhanced Protected Mode”
6. Click OK and restart the browser

How to convert a byte array to its numeric value (Java)?

public static long byteArrayToLong(byte[] bytes) {
    return ((long) (bytes[0]) << 56)
            + (((long) bytes[1] & 0xFF) << 48)
            + ((long) (bytes[2] & 0xFF) << 40)
            + ((long) (bytes[3] & 0xFF) << 32)
            + ((long) (bytes[4] & 0xFF) << 24)
            + ((bytes[5] & 0xFF) << 16)
            + ((bytes[6] & 0xFF) << 8)
            + (bytes[7] & 0xFF);
}

convert bytes array (long is 8 bytes) to long

How to remove specific object from ArrayList in Java?

If you want to remove multiple objects that are matching to the property try this.

I have used following code to remove element from object array it helped me.

In general an object can be removed in two ways from an ArrayList (or generally any List), by index (remove(int)) and by object (remove(Object)).

some time for you arrayList.remove(index)or arrayList.remove(obj.get(index)) using these lines may not work try to use following code.

for (Iterator<DetailInbox> iter = detailInboxArray.iterator(); iter.hasNext(); ) {
    DetailInbox element = iter.next();
   if (element.isSelected()) {
      iter.remove();
   }
}

svn list of files that are modified in local copy

I couldn't get svn status -q to work. Assuming you are on a linux box, to see only the files that are modified, run: svn status | grep 'M ' On windows I am not sure what you would do, maybe something with 'FindStr'

Show DataFrame as table in iPython Notebook

This answer is based on the 2nd tip from this blog post: 28 Jupyter Notebook tips, tricks and shortcuts

You can add the following code to the top of your notebook

from IPython.core.interactiveshell import InteractiveShell
InteractiveShell.ast_node_interactivity = "all"

This tells Jupyter to print the results for any variable or statement on it’s own line. So you can then execute a cell solely containing

df1
df2

and it will "print out the beautiful tables for both datasets".

jQuery selector regular expressions

I'm just giving my real time example:

In native javascript I used following snippet to find the elements with ids starts with "select2-qownerName_select-result".

document.querySelectorAll("[id^='select2-qownerName_select-result']");

When we shifted from javascript to jQuery we've replaced above snippet with the following which involves less code changes without disturbing the logic.

$("[id^='select2-qownerName_select-result']")

Forcing a postback

You can manually call the method invoked by PostBack from the Page_Load event:

public void Page_Load(object sender, EventArgs e)
{
    MyPostBackMethod(sender, e);
}

But if you mean if you can have the Page.IsPostBack property set to true without real post back, then the answer is no.

How can I convert an HTML table to CSV?

Here's a ruby script that uses nokogiri -- http://nokogiri.rubyforge.org/nokogiri/

require 'nokogiri'

doc = Nokogiri::HTML(table_string)

doc.xpath('//table//tr').each do |row|
  row.xpath('td').each do |cell|
    print '"', cell.text.gsub("\n", ' ').gsub('"', '\"').gsub(/(\s){2,}/m, '\1'), "\", "
  end
  print "\n"
end

Worked for my basic test case.

Avoid duplicates in INSERT INTO SELECT query in SQL Server

In MySQL you can do this:

INSERT IGNORE INTO Table2(Id, Name) SELECT Id, Name FROM Table1

Does SQL Server have anything similar?

[Vue warn]: Property or method is not defined on the instance but referenced during render

Should anybody land with the same silly problem I had, make sure your component has the 'data' property spelled correctly. (eg. data, and not date)

<template>
    <span>{{name}}</span>
</template>

<script>
export default {
  name: "MyComponent",
  data() {
    return {
      name: ""
    };
  }
</script>

How do I connect to a SQL Server 2008 database using JDBC?

There are mainly two ways to use JDBC - using Windows authentication and SQL authentication. SQL authentication is probably the easiest. What you can do is something like:

String userName = "username";
String password = "password";

String url = "jdbc:sqlserver://MYPC\\SQLEXPRESS;databaseName=MYDB";

Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
Connection conn = DriverManager.getConnection(url, userName, password);

after adding sqljdbc4.jar to the build path.

For Window authentication you can do something like:

String url = "jdbc:sqlserver://MYPC\\SQLEXPRESS;databaseName=MYDB;integratedSecurity=true";
Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
Connection conn = DriverManager.getConnection(url);

and then add the path to sqljdbc_auth.dll as a VM argument (still need sqljdbc4.jar in the build path).

Please take a look here for a short step-by-step guide showing how to connect to SQL Server from Java using jTDS and JDBC should you need more details. Hope it helps!

Updating property value in properties file without deleting other values

Open the output stream and store properties after you have closed the input stream.

FileInputStream in = new FileInputStream("First.properties");
Properties props = new Properties();
props.load(in);
in.close();

FileOutputStream out = new FileOutputStream("First.properties");
props.setProperty("country", "america");
props.store(out, null);
out.close();

What is the difference between RTP or RTSP in a streaming server?

I hear your pain. I'm going through this right now (years later). From what I've learned, you can think of RTSP as a "VCR controller", the protocol allows you to specify which streams (presentations) you want to play, it will then send you a description of the media, and then you can use RTSP to play, stop, pause, and record the remote stream. The media itself goes over RTP. RTSP is normally implemented over a different socket or communication layer. Although it is simply a protocol, most often it's implemented by a server over a socket. For live streams, the RTSP stream you request is simply a name of a stream. It doesn't need to refer to a file on the server, the server's RTSP implementation can parse that stream, put together a live graph, and then provide the SDP (description) for that stream name. But, this is of course specific to the way the RTSP server has been implemented. For "live" streams, it's probably simpler to just use RTP, but you'll need a way to transfer the SDP from the RTP server to the client that wants to play that stream.

How to reload the datatable(jquery) data?

None of these solutions worked for me, but I did do something similar to Masood's answer. Here it is for posterity. This assumes you have <table id="mytable"></table> in your page somewhere:

function generate_support_user_table() {
        $('#mytable').hide();
        $('#mytable').dataTable({
            ...
            "bDestroy": true,
            "fnInitComplete": function () { $('#support_user_table').show(); },
            ...
        });
}

The important parts are:

  1. bDestroy, which wipes out the current table before loading.
  2. The hide() call and fnInitComplete, which ensures that the table only appears after everything is loaded. Otherwise it resizes and looks weird while loading.

Just add the function call to $(document).ready() and you should be all set. It will load the table initially, as well as reload later on a button click or whatever.

Hide/Show Column in an HTML Table

<p><input type="checkbox" name="ch1" checked="checked" /> First Name</p>
.... 
<td class="ch1">...</td>

 <script>
       $(document).ready(function() {
            $('#demo').multiselect();
        });


        $("input:checkbox:not(:checked)").each(function() {
    var column = "table ." + $(this).attr("name");
    $(column).hide();
});

$("input:checkbox").click(function(){
    var column = "table ." + $(this).attr("name");
    $(column).toggle();
});
 </script>

How can I call the 'base implementation' of an overridden virtual method?

You can't do it by C#, but you can edit MSIL.

IL code of your Main method:

.method private hidebysig static void Main() cil managed
{
    .entrypoint
    .maxstack 1
    .locals init (
        [0] class MsilEditing.A a)
    L_0000: nop 
    L_0001: newobj instance void MsilEditing.B::.ctor()
    L_0006: stloc.0 
    L_0007: ldloc.0 
    L_0008: callvirt instance void MsilEditing.A::X()
    L_000d: nop 
    L_000e: ret 
}

You should change opcode in L_0008 from callvirt to call

L_0008: call instance void MsilEditing.A::X()

How can I get screen resolution in java?

int screenResolution = Toolkit.getDefaultToolkit().getScreenResolution();
System.out.println(""+screenResolution);

Bind event to right mouse click

Is contextmenu an event?

I would use onmousedown or onclick then grab the MouseEvent's button property to determine which button was pressed (0 = left, 1 = middle, 2 = right).

How do I prevent the error "Index signature of object type implicitly has an 'any' type" when compiling typescript with noImplicitAny flag enabled?

use keyof typeof

const cat = {
    name: 'tuntun'
}

const key: string = 'name' 

cat[key as keyof typeof cat]

How do you programmatically set an attribute?

setattr(x, attr, 'magic')

For help on it:

>>> help(setattr)
Help on built-in function setattr in module __builtin__:

setattr(...)
    setattr(object, name, value)

    Set a named attribute on an object; setattr(x, 'y', v) is equivalent to
    ``x.y = v''.

Edit: However, you should note (as pointed out in a comment) that you can't do that to a "pure" instance of object. But it is likely you have a simple subclass of object where it will work fine. I would strongly urge the O.P. to never make instances of object like that.

Why is there no multiple inheritance in Java, but implementing multiple interfaces is allowed?

For the same reason C# doesn't allow multiple inheritence but allows you to implement multiple interfaces.

The lesson learned from C++ w/ multiple inheritence was that it lead to more issues than it was worth.

An interface is a contract of things your class has to implement. You don't gain any functionality from the interface. Inheritence allows you to inherit the functionality of a parent class (and in multiple-inheritence, that can get extremely confusing).

Allowing multiple interfaces allows you to use Design Patterns (like Adapter) to solve the same types of issues you can solve using multiple inheritence, but in a much more reliable and predictable manner.

Copy folder recursively in Node.js

I wrote this function for both copying (copyFileSync) or moving (renameSync) files recursively between directories:

// Copy files
copyDirectoryRecursiveSync(sourceDir, targetDir);
// Move files
copyDirectoryRecursiveSync(sourceDir, targetDir, true);


function copyDirectoryRecursiveSync(source, target, move) {
    if (!fs.lstatSync(source).isDirectory())
        return;

    var operation = move ? fs.renameSync : fs.copyFileSync;
    fs.readdirSync(source).forEach(function (itemName) {
        var sourcePath = path.join(source, itemName);
        var targetPath = path.join(target, itemName);

        if (fs.lstatSync(sourcePath).isDirectory()) {
            fs.mkdirSync(targetPath);
            copyDirectoryRecursiveSync(sourcePath, targetDir);
        }
        else {
            operation(sourcePath, targetPath);
        }
    });
}

Where does PHP store the error log? (php5, apache, fastcgi, cpanel)

The best way is to look in your httpd.conf file and see what the default is. It could also be overridden by your specific virtual host. I start by looking at /etc/httpd/conf/httpd.conf or /etc/apache2/httpd.conf and search for error_log. It could be listed as either /var/log/httpd/error_log or /var/log/apache2/error_log but it might also be listed as simply logs/error_log.

In this case it is a relative path, which means it will be under /etc/httpd/logs/error_log. If you still can't find it check the bottom of your httpd.conf file and see where your virtual hosts are included. It might be in /etc/httpd/conf.d/<- as "other" or "extra". Your virtual host could override it then with ErrorLog "/path/to/error_log".

How to Detect Browser Window /Tab Close Event?

Yes there is! After a lot of headache i found one solution to this.

Monitor.php

This php file will be monitoring the browser close event. Once the browser is closed the connection_aborted will return 1 hence the loop will break.

<?php
// Ignore user aborts and allow the script
// to run forever
ignore_user_abort(true);
set_time_limit(0);

echo connection_aborted();
while(1)
{
echo "Whatever you echo here wont be printed anywhere but it is required in order to work.";
flush();
if(connection_aborted())
{
break;
// Breaks only when browser is closed
}
}

/*
Action you want to take after browser is closed.
Write your code here
*/
?>

Caller.php

This is the file which will call Monitor.php

<?php
Header('Location: monitor.php');
?>

Parent.html

This will be the file which you will actually interact with. On loading this will directly make an AJAX call to Caller.php which will automatically start Monitor.php in background mode.

<script>

 var xmlhttp = new XMLHttpRequest();
        xmlhttp.onreadystatechange = function() {
            if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {

            }
         }

   xmlhttp.open("GET", "Caller.php", true);
        xmlhttp.send();   

</script>

So the final flow is Parent.html----->Caller.php----->Monitor.php

Execute Shell Script after post build in Jenkins

If I'm reading your question right, you want to run a script in the post build actions part of the build.

I myself use PostBuildScript Plugin for running git clean -fxd after the build has archived artifacts and published test results. My Jenkins slaves have SSD disks, so I do not have the room keep generated files in the workspace.

How to parse a String containing XML in Java and retrieve the value of the root node?

You could do this with JAXB (an implementation is included in Java SE 6).

import java.io.StringReader;
import javax.xml.bind.*;
import javax.xml.transform.stream.StreamSource;

public class Demo {

    public static void main(String[] args) throws Exception {
        String xmlString = "<message>HELLO!</message> ";
        JAXBContext jc = JAXBContext.newInstance(String.class);
        Unmarshaller unmarshaller = jc.createUnmarshaller();
        StreamSource xmlSource = new StreamSource(new StringReader(xmlString));
        JAXBElement<String> je = unmarshaller.unmarshal(xmlSource, String.class);
        System.out.println(je.getValue());
    }

}

Output

HELLO!

How to change scroll bar position with CSS?

Here is another way, by rotating element with the scrollbar for 180deg, wrapping it's content into another element, and rotating that wrapper for -180deg. Check the snippet below

_x000D_
_x000D_
div {_x000D_
  display: inline-block;_x000D_
  width: 100px;_x000D_
  height: 100px;_x000D_
  border: 2px solid black;_x000D_
  margin: 15px;_x000D_
}_x000D_
#vertical {_x000D_
  direction: rtl;_x000D_
  overflow-y: scroll;_x000D_
  overflow-x: hidden;_x000D_
  background: gold;_x000D_
}_x000D_
#vertical p {_x000D_
  direction: ltr;_x000D_
  margin-bottom: 0;_x000D_
}_x000D_
#horizontal {_x000D_
  direction: rtl;_x000D_
  transform: rotate(180deg);_x000D_
  overflow-y: hidden;_x000D_
  overflow-x: scroll;_x000D_
  background: tomato;_x000D_
  padding-top: 30px;_x000D_
}_x000D_
#horizontal span {_x000D_
  direction: ltr;_x000D_
  display: inline-block;_x000D_
  transform: rotate(-180deg);_x000D_
}
_x000D_
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>_x000D_
<div id=vertical>_x000D_
  <p>content_x000D_
    <br>content_x000D_
    <br>content_x000D_
    <br>content_x000D_
    <br>content_x000D_
    <br>content_x000D_
    <br>content_x000D_
    <br>content_x000D_
    <br>content_x000D_
    <br>content_x000D_
    <br>content_x000D_
    <br>content_x000D_
    <br>content</p>_x000D_
</div>_x000D_
<div id=horizontal><span> content_content_content_content_content_content_content_content_content_content_content_content_content_content</span>_x000D_
</div>
_x000D_
_x000D_
_x000D_

Get a list of checked checkboxes in a div using jQuery

function listselect() {
                var selected = [];
                $('.SelectPhone').prop('checked', function () {

                    selected.push($(this).val());
                });

                alert(selected.length);
     <input type="checkbox" name="SelectPhone" class="SelectPhone"  value="1" />
         <input type="checkbox" name="SelectPhone" class="SelectPhone"  value="2" />
         <input type="checkbox" name="SelectPhone" class="SelectPhone"  value="3" />
        <button onclick="listselect()">show count</button>

AssertNull should be used or AssertNotNull

I just want to add that if you want to write special text if It null than you make it like that

  Assert.assertNotNull("The object you enter return null", str1)

Is there a way to word-wrap long words in a div?

You can try specifying a width for the div, whether it be in pixels, percentages or ems, and at that point the div will remain that width and the text will wrap automatically then within the div.

MySQL vs MySQLi when using PHP

There is a manual page dedicated to help choosing between mysql, mysqli and PDO at

The PHP team recommends mysqli or PDO_MySQL for new development:

It is recommended to use either the mysqli or PDO_MySQL extensions. It is not recommended to use the old mysql extension for new development. A detailed feature comparison matrix is provided below. The overall performance of all three extensions is considered to be about the same. Although the performance of the extension contributes only a fraction of the total run time of a PHP web request. Often, the impact is as low as 0.1%.

The page also has a feature matrix comparing the extension APIs. The main differences between mysqli and mysql API are as follows:

                               mysqli     mysql
Development Status             Active     Maintenance only
Lifecycle                      Active     Long Term Deprecation Announced*
Recommended                    Yes        No
OOP API                        Yes        No
Asynchronous Queries           Yes        No
Server-Side Prep. Statements   Yes        No
Stored Procedures              Yes        No
Multiple Statements            Yes        No
Transactions                   Yes        No
MySQL 5.1+ functionality       Yes        No

* http://news.php.net/php.internals/53799

There is an additional feature matrix comparing the libraries (new mysqlnd versus libmysql) at

and a very thorough blog article at

What is trunk, branch and tag in Subversion?

If you're new to Subversion you may want to check out this post on SmashingMagazine.com, appropriately titled Ultimate Round-Up for Version Control with SubVersion.

It covers getting started with SubVersion with links to tutorials, reference materials, & book suggestions.

It covers tools (many are compatible windows), and it mentions AnkhSVN as a Visual Studio compatible plugin. The comments also mention VisualSVN as an alternative.

Changing default encoding of Python?

This fixed the issue for me.

import os
os.environ["PYTHONIOENCODING"] = "utf-8"

Is it possible to center text in select box?

I'm afraid this isn't possible with plain CSS, and won't be possible to make completely cross-browser compatible.

However, using a jQuery plugin, you could style the dropdown:

https://www.filamentgroup.com/lab/jquery-ui-selectmenu-an-aria-accessible-plugin-for-styling-a-html-select.html

This plugin hides the select element, and creates span elements etc on the fly to display a custom drop down list style. I'm quite confident you'd be able to change the styles on the spans etc to center align the items.

How to remove files and directories quickly via terminal (bash shell)

So I was looking all over for a way to remove all files in a directory except for some directories, and files, I wanted to keep around. After much searching I devised a way to do it using find.

find -E . -regex './(dir1|dir2|dir3)' -and -type d -prune -o -print -exec rm -rf {} \;

Essentially it uses regex to select the directories to exclude from the results then removes the remaining files. Just wanted to put it out here in case someone else needed it.

Does HTTP use UDP?

In theory yes it is possible to use UDP for http but that might be problematic. Say for instance in your example a mp3 or a video is being streamed there will be problem of ordering and some bits might go missing as UDP is not connection oriented there is no retransmit mechanism.

Writing new lines to a text file in PowerShell

You can use the Environment class's static NewLine property to get the proper newline:

$errorMsg =  "{0} Error {1}{2} key {3} expected: {4}{5} local value is: {6}" -f `
               (Get-Date),$keyPath,$value,$key,$policyValue,([Environment]::NewLine),$localValue
Add-Content -Path $logpath $errorMsg

Difference between drop table and truncate table?

DELETE VS TRUNCATE

  1. The DELETE statement removes rows one at a time and records an entry in the transaction log for each deleted row. TRUNCATE TABLE removes the data by deallocating the data pages used to store the table data and records only the page deallocations in the transaction log
  2. We can use WHERE clause in DELETE but in TRUNCATE you cannot use it
  3. When the DELETE statement is executed using a row lock, each row in the table is locked for deletion. TRUNCATE TABLE always locks the table and page but not each row
  4. After a DELETE statement is executed, the table can still contain empty pages.If the delete operation does not use a table lock, the table (heap) will contain many empty pages. For indexes, the delete operation can leave empty pages behind, although these
    pages will be deallocated quickly by a background cleanup process
  5. TRUNCATE TABLE removes all rows from a table, but the table structure and its columns, constraints, indexes, and so on remain
  6. DELETE statement doesn't RESEED identity column but TRUNCATE statement RESEEDS the IDENTITY column
  7. You cannot use TRUNCATE TABLE on tables that:
    1. Are referenced by a FOREIGN KEY constraint. (You can truncate a table that has a foreign key that references itself.)
    2. Participate in an indexed view.
    3. Are published by using transactional replication or merge replication
  8. TRUNCATE TABLE cannot activate a trigger because the operation does not log individual row deletions

get string from right hand side

Simplest solution:

substr('299123456',-6,6)

How to increment a JavaScript variable using a button press event

<script type="text/javascript">
var i=0;

function increase()
{
    i++;
    return false;
}</script><input type="button" onclick="increase();">

How to replace all strings to numbers contained in each string in Notepad++?

I have Notepad++ v6.8.8

Find: [([a-zA-Z])]

Replace: [\'\1\']

Will produce: $array[XYZ] => $array['XYZ']

How to set button click effect in Android?

For all the views

android:background="?android:attr/selectableItemBackground"

But for cardview which has elevation use

android:foreground="?android:attr/selectableItemBackground"

For Circular click effect as in toolbar

android:background="?android:attr/actionBarItemBackground"

Also you need to set

 android:clickable="true"
 android:focusable="true"

How to access URL segment(s) in blade in Laravel 5?

The double curly brackets are processed via Blade -- not just plain PHP. This syntax basically echos the calculated value.

{{ Request::segment(1) }} 

How to delete only the content of file in python

You can do this:

def deleteContent(pfile):
    fn=pfile.name 
    pfile.close()
    return open(fn,'w')

How do I make a batch file terminate upon encountering an error?

Add || goto :label to each line, and then define a :label.

For example, create this .cmd file:

@echo off

echo Starting very complicated batch file...
ping -invalid-arg || goto :error
echo OH noes, this shouldn't have succeeded.
goto :EOF

:error
echo Failed with error #%errorlevel%.
exit /b %errorlevel%

See also question about exiting batch file subroutine.

How to update one file in a zip archive

yes its possible.

on linux based systems just install zip and you can call it in the command line. have a look at the manpage: http://linux.die.net/man/1/zip

but in my personal experience, if possible and compression is not so important, this works better with plain tar files and tar.

How to rename a table column in Oracle 10g

alter table table_name rename column oldColumn to newColumn;

How can I use modulo operator (%) in JavaScript?

That would be the modulo operator, which produces the remainder of the division of two numbers.

Pandas dataframe get first row of each group

>>> df.groupby('id').first()
     value
id        
1    first
2    first
3    first
4   second
5    first
6    first
7   fourth

If you need id as column:

>>> df.groupby('id').first().reset_index()
   id   value
0   1   first
1   2   first
2   3   first
3   4  second
4   5   first
5   6   first
6   7  fourth

To get n first records, you can use head():

>>> df.groupby('id').head(2).reset_index(drop=True)
    id   value
0    1   first
1    1  second
2    2   first
3    2  second
4    3   first
5    3   third
6    4  second
7    4   fifth
8    5   first
9    6   first
10   6  second
11   7  fourth
12   7   fifth

Oracle SqlPlus - saving output in a file but don't show on screen

Try this:

SET TERMOUT OFF; 
spool M:\Documents\test;
select * from employees;
/
spool off;

Angular 6 Material mat-select change method removed

If you're using Reactive forms you can listen for changes to the select control like so..

this.form.get('mySelectControl').valueChanges.subscribe(value => { ... do stuff ... })

Limit Decimal Places in Android EditText

This is to build on pinhassi's answer - the issue that I came across was that you couldn't add values before the decimal once the decimal limit has been reached. To fix the issue, we need to construct the final string before doing the pattern match.

import java.util.regex.Matcher;
import java.util.regex.Pattern;

import android.text.InputFilter;
import android.text.Spanned;

public class DecimalLimiter implements InputFilter
{
    Pattern mPattern;

    public DecimalLimiter(int digitsBeforeZero,int digitsAfterZero) 
    {
        mPattern=Pattern.compile("[0-9]{0," + (digitsBeforeZero) + "}+((\\.[0-9]{0," + (digitsAfterZero) + "})?)||(\\.)?");
    }

    @Override
    public CharSequence filter(CharSequence source, int start, int end, Spanned dest, int dstart, int dend) 
    {
        StringBuilder sb = new StringBuilder(dest);
        sb.insert(dstart, source, start, end);

        Matcher matcher = mPattern.matcher(sb.toString());
        if(!matcher.matches())
            return "";
        return null;
    }
}

Install Visual Studio 2013 on Windows 7

Fake IE10 to install Visual Studio 2013

Visual Studio 2013 requires Internet Explorer 10. If you try to install it on Windows 7 with IE8 you get the following error This version of Visual Studio requires Internet Explorer 10”. The value that the VS 2013 installer checks is svcVersion in the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorerkey on 32-bit Windows and HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Internet Explorer on 64-bit Windows. Any value >= 10.0.0.0 makes the installer happy.

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer]
"svcVersion"="10.0.0.0"

[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Internet Explorer]
"svcVersion"="10.0.0.0"

Minimum and maximum value of z-index?

Z-Index only works for elements that have position: relative; or position: absolute; applied to them. If that's not the problem we'll need to see an example page to be more helpful.

EDIT: The good doctor has already put the fullest explanation but the quick version is that the minimum is 0 because it can't be a negative number and the maximum - well, you'll never really need to go above 10 for most designs.

how can I display tooltip or item information on mouse over?

The simplest way to get tooltips in most browsers is to set some text in the title attribute.

eg.

<img src="myimage.jpg" alt="a cat" title="My cat sat on a table" />

produces (hover your mouse over the image):

a cat http://www.imagechicken.com/uploads/1275939952008633500.jpg

Title attributes can be applied to most HTML elements.

Clearing a string buffer/builder after loop

public void clear(StringBuilder s) {
    s.setLength(0);
}

Usage:

StringBuilder v = new StringBuilder();
clear(v);

for readability, I think this is the best solution.

How to generate javadoc comments in Android Studio

Android Studio -> Preferences -> Editor -> Intentions -> Java -> Declaration -> Enable "Add JavaDoc"

And, While selecting Methods to Implement (Ctrl/Cmd + i), on the left bottom, you should be seeing checkbox to enable Copy JavaDoc.

How to Validate Google reCaptcha on Form Submit

Try this link: https://github.com/google/ReCAPTCHA/tree/master/php

A link to that page is posted at the very bottom of this page: https://developers.google.com/recaptcha/intro

One issue I came up with that prevented these two files from working correctly was with my php.ini file for the website. Make sure this property is setup properly, as follows: allow_url_fopen = On

Difference between numpy dot() and Python 3.5+ matrix multiplication @

Just FYI, @ and its numpy equivalents dot and matmul are all equally fast. (Plot created with perfplot, a project of mine.)

enter image description here

Code to reproduce the plot:

import perfplot
import numpy


def setup(n):
    A = numpy.random.rand(n, n)
    x = numpy.random.rand(n)
    return A, x


def at(data):
    A, x = data
    return A @ x


def numpy_dot(data):
    A, x = data
    return numpy.dot(A, x)


def numpy_matmul(data):
    A, x = data
    return numpy.matmul(A, x)


perfplot.show(
    setup=setup,
    kernels=[at, numpy_dot, numpy_matmul],
    n_range=[2 ** k for k in range(15)],
)

Best practice for REST token-based authentication with JAX-RS and Jersey

How token-based authentication works

In token-based authentication, the client exchanges hard credentials (such as username and password) for a piece of data called token. For each request, instead of sending the hard credentials, the client will send the token to the server to perform authentication and then authorization.

In a few words, an authentication scheme based on tokens follow these steps:

  1. The client sends their credentials (username and password) to the server.
  2. The server authenticates the credentials and, if they are valid, generate a token for the user.
  3. The server stores the previously generated token in some storage along with the user identifier and an expiration date.
  4. The server sends the generated token to the client.
  5. The client sends the token to the server in each request.
  6. The server, in each request, extracts the token from the incoming request. With the token, the server looks up the user details to perform authentication.
    • If the token is valid, the server accepts the request.
    • If the token is invalid, the server refuses the request.
  7. Once the authentication has been performed, the server performs authorization.
  8. The server can provide an endpoint to refresh tokens.

Note: The step 3 is not required if the server has issued a signed token (such as JWT, which allows you to perform stateless authentication).

What you can do with JAX-RS 2.0 (Jersey, RESTEasy and Apache CXF)

This solution uses only the JAX-RS 2.0 API, avoiding any vendor specific solution. So, it should work with JAX-RS 2.0 implementations, such as Jersey, RESTEasy and Apache CXF.

It is worthwhile to mention that if you are using token-based authentication, you are not relying on the standard Java EE web application security mechanisms offered by the servlet container and configurable via application's web.xml descriptor. It's a custom authentication.

Authenticating a user with their username and password and issuing a token

Create a JAX-RS resource method which receives and validates the credentials (username and password) and issue a token for the user:

@Path("/authentication")
public class AuthenticationEndpoint {

    @POST
    @Produces(MediaType.APPLICATION_JSON)
    @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
    public Response authenticateUser(@FormParam("username") String username, 
                                     @FormParam("password") String password) {

        try {

            // Authenticate the user using the credentials provided
            authenticate(username, password);

            // Issue a token for the user
            String token = issueToken(username);

            // Return the token on the response
            return Response.ok(token).build();

        } catch (Exception e) {
            return Response.status(Response.Status.FORBIDDEN).build();
        }      
    }

    private void authenticate(String username, String password) throws Exception {
        // Authenticate against a database, LDAP, file or whatever
        // Throw an Exception if the credentials are invalid
    }

    private String issueToken(String username) {
        // Issue a token (can be a random String persisted to a database or a JWT token)
        // The issued token must be associated to a user
        // Return the issued token
    }
}

If any exceptions are thrown when validating the credentials, a response with the status 403 (Forbidden) will be returned.

If the credentials are successfully validated, a response with the status 200 (OK) will be returned and the issued token will be sent to the client in the response payload. The client must send the token to the server in every request.

When consuming application/x-www-form-urlencoded, the client must to send the credentials in the following format in the request payload:

username=admin&password=123456

Instead of form params, it's possible to wrap the username and the password into a class:

public class Credentials implements Serializable {

    private String username;
    private String password;

    // Getters and setters omitted
}

And then consume it as JSON:

@POST
@Produces(MediaType.APPLICATION_JSON)
@Consumes(MediaType.APPLICATION_JSON)
public Response authenticateUser(Credentials credentials) {

    String username = credentials.getUsername();
    String password = credentials.getPassword();

    // Authenticate the user, issue a token and return a response
}

Using this approach, the client must to send the credentials in the following format in the payload of the request:

{
  "username": "admin",
  "password": "123456"
}

Extracting the token from the request and validating it

The client should send the token in the standard HTTP Authorization header of the request. For example:

Authorization: Bearer <token-goes-here>

The name of the standard HTTP header is unfortunate because it carries authentication information, not authorization. However, it's the standard HTTP header for sending credentials to the server.

JAX-RS provides @NameBinding, a meta-annotation used to create other annotations to bind filters and interceptors to resource classes and methods. Define a @Secured annotation as following:

@NameBinding
@Retention(RUNTIME)
@Target({TYPE, METHOD})
public @interface Secured { }

The above defined name-binding annotation will be used to decorate a filter class, which implements ContainerRequestFilter, allowing you to intercept the request before it be handled by a resource method. The ContainerRequestContext can be used to access the HTTP request headers and then extract the token:

@Secured
@Provider
@Priority(Priorities.AUTHENTICATION)
public class AuthenticationFilter implements ContainerRequestFilter {

    private static final String REALM = "example";
    private static final String AUTHENTICATION_SCHEME = "Bearer";

    @Override
    public void filter(ContainerRequestContext requestContext) throws IOException {

        // Get the Authorization header from the request
        String authorizationHeader =
                requestContext.getHeaderString(HttpHeaders.AUTHORIZATION);

        // Validate the Authorization header
        if (!isTokenBasedAuthentication(authorizationHeader)) {
            abortWithUnauthorized(requestContext);
            return;
        }

        // Extract the token from the Authorization header
        String token = authorizationHeader
                            .substring(AUTHENTICATION_SCHEME.length()).trim();

        try {

            // Validate the token
            validateToken(token);

        } catch (Exception e) {
            abortWithUnauthorized(requestContext);
        }
    }

    private boolean isTokenBasedAuthentication(String authorizationHeader) {

        // Check if the Authorization header is valid
        // It must not be null and must be prefixed with "Bearer" plus a whitespace
        // The authentication scheme comparison must be case-insensitive
        return authorizationHeader != null && authorizationHeader.toLowerCase()
                    .startsWith(AUTHENTICATION_SCHEME.toLowerCase() + " ");
    }

    private void abortWithUnauthorized(ContainerRequestContext requestContext) {

        // Abort the filter chain with a 401 status code response
        // The WWW-Authenticate header is sent along with the response
        requestContext.abortWith(
                Response.status(Response.Status.UNAUTHORIZED)
                        .header(HttpHeaders.WWW_AUTHENTICATE, 
                                AUTHENTICATION_SCHEME + " realm=\"" + REALM + "\"")
                        .build());
    }

    private void validateToken(String token) throws Exception {
        // Check if the token was issued by the server and if it's not expired
        // Throw an Exception if the token is invalid
    }
}

If any problems happen during the token validation, a response with the status 401 (Unauthorized) will be returned. Otherwise the request will proceed to a resource method.

Securing your REST endpoints

To bind the authentication filter to resource methods or resource classes, annotate them with the @Secured annotation created above. For the methods and/or classes that are annotated, the filter will be executed. It means that such endpoints will only be reached if the request is performed with a valid token.

If some methods or classes do not need authentication, simply do not annotate them:

@Path("/example")
public class ExampleResource {

    @GET
    @Path("{id}")
    @Produces(MediaType.APPLICATION_JSON)
    public Response myUnsecuredMethod(@PathParam("id") Long id) {
        // This method is not annotated with @Secured
        // The authentication filter won't be executed before invoking this method
        ...
    }

    @DELETE
    @Secured
    @Path("{id}")
    @Produces(MediaType.APPLICATION_JSON)
    public Response mySecuredMethod(@PathParam("id") Long id) {
        // This method is annotated with @Secured
        // The authentication filter will be executed before invoking this method
        // The HTTP request must be performed with a valid token
        ...
    }
}

In the example shown above, the filter will be executed only for the mySecuredMethod(Long) method because it's annotated with @Secured.

Identifying the current user

It's very likely that you will need to know the user who is performing the request agains your REST API. The following approaches can be used to achieve it:

Overriding the security context of the current request

Within your ContainerRequestFilter.filter(ContainerRequestContext) method, a new SecurityContext instance can be set for the current request. Then override the SecurityContext.getUserPrincipal(), returning a Principal instance:

final SecurityContext currentSecurityContext = requestContext.getSecurityContext();
requestContext.setSecurityContext(new SecurityContext() {

        @Override
        public Principal getUserPrincipal() {
            return () -> username;
        }

    @Override
    public boolean isUserInRole(String role) {
        return true;
    }

    @Override
    public boolean isSecure() {
        return currentSecurityContext.isSecure();
    }

    @Override
    public String getAuthenticationScheme() {
        return AUTHENTICATION_SCHEME;
    }
});

Use the token to look up the user identifier (username), which will be the Principal's name.

Inject the SecurityContext in any JAX-RS resource class:

@Context
SecurityContext securityContext;

The same can be done in a JAX-RS resource method:

@GET
@Secured
@Path("{id}")
@Produces(MediaType.APPLICATION_JSON)
public Response myMethod(@PathParam("id") Long id, 
                         @Context SecurityContext securityContext) {
    ...
}

And then get the Principal:

Principal principal = securityContext.getUserPrincipal();
String username = principal.getName();

Using CDI (Context and Dependency Injection)

If, for some reason, you don't want to override the SecurityContext, you can use CDI (Context and Dependency Injection), which provides useful features such as events and producers.

Create a CDI qualifier:

@Qualifier
@Retention(RUNTIME)
@Target({ METHOD, FIELD, PARAMETER })
public @interface AuthenticatedUser { }

In your AuthenticationFilter created above, inject an Event annotated with @AuthenticatedUser:

@Inject
@AuthenticatedUser
Event<String> userAuthenticatedEvent;

If the authentication succeeds, fire the event passing the username as parameter (remember, the token is issued for a user and the token will be used to look up the user identifier):

userAuthenticatedEvent.fire(username);

It's very likely that there's a class that represents a user in your application. Let's call this class User.

Create a CDI bean to handle the authentication event, find a User instance with the correspondent username and assign it to the authenticatedUser producer field:

@RequestScoped
public class AuthenticatedUserProducer {

    @Produces
    @RequestScoped
    @AuthenticatedUser
    private User authenticatedUser;

    public void handleAuthenticationEvent(@Observes @AuthenticatedUser String username) {
        this.authenticatedUser = findUser(username);
    }

    private User findUser(String username) {
        // Hit the the database or a service to find a user by its username and return it
        // Return the User instance
    }
}

The authenticatedUser field produces a User instance that can be injected into container managed beans, such as JAX-RS services, CDI beans, servlets and EJBs. Use the following piece of code to inject a User instance (in fact, it's a CDI proxy):

@Inject
@AuthenticatedUser
User authenticatedUser;

Note that the CDI @Produces annotation is different from the JAX-RS @Produces annotation:

Be sure you use the CDI @Produces annotation in your AuthenticatedUserProducer bean.

The key here is the bean annotated with @RequestScoped, allowing you to share data between filters and your beans. If you don't wan't to use events, you can modify the filter to store the authenticated user in a request scoped bean and then read it from your JAX-RS resource classes.

Compared to the approach that overrides the SecurityContext, the CDI approach allows you to get the authenticated user from beans other than JAX-RS resources and providers.

Supporting role-based authorization

Please refer to my other answer for details on how to support role-based authorization.

Issuing tokens

A token can be:

  • Opaque: Reveals no details other than the value itself (like a random string)
  • Self-contained: Contains details about the token itself (like JWT).

See details below:

Random string as token

A token can be issued by generating a random string and persisting it to a database along with the user identifier and an expiration date. A good example of how to generate a random string in Java can be seen here. You also could use:

Random random = new SecureRandom();
String token = new BigInteger(130, random).toString(32);

JWT (JSON Web Token)

JWT (JSON Web Token) is a standard method for representing claims securely between two parties and is defined by the RFC 7519.

It's a self-contained token and it enables you to store details in claims. These claims are stored in the token payload which is a JSON encoded as Base64. Here are some claims registered in the RFC 7519 and what they mean (read the full RFC for further details):

  • iss: Principal that issued the token.
  • sub: Principal that is the subject of the JWT.
  • exp: Expiration date for the token.
  • nbf: Time on which the token will start to be accepted for processing.
  • iat: Time on which the token was issued.
  • jti: Unique identifier for the token.

Be aware that you must not store sensitive data, such as passwords, in the token.

The payload can be read by the client and the integrity of the token can be easily checked by verifying its signature on the server. The signature is what prevents the token from being tampered with.

You won't need to persist JWT tokens if you don't need to track them. Althought, by persisting the tokens, you will have the possibility of invalidating and revoking the access of them. To keep the track of JWT tokens, instead of persisting the whole token on the server, you could persist the token identifier (jti claim) along with some other details such as the user you issued the token for, the expiration date, etc.

When persisting tokens, always consider removing the old ones in order to prevent your database from growing indefinitely.

Using JWT

There are a few Java libraries to issue and validate JWT tokens such as:

To find some other great resources to work with JWT, have a look at http://jwt.io.

Handling token revocation with JWT

If you want to revoke tokens, you must keep the track of them. You don't need to store the whole token on server side, store only the token identifier (that must be unique) and some metadata if you need. For the token identifier you could use UUID.

The jti claim should be used to store the token identifier on the token. When validating the token, ensure that it has not been revoked by checking the value of the jti claim against the token identifiers you have on server side.

For security purposes, revoke all the tokens for a user when they change their password.

Additional information

  • It doesn't matter which type of authentication you decide to use. Always do it on the top of a HTTPS connection to prevent the man-in-the-middle attack.
  • Take a look at this question from Information Security for more information about tokens.
  • In this article you will find some useful information about token-based authentication.

What’s the best way to check if a file exists in C++? (cross platform)

Be careful of race conditions: if the file disappears between the "exists" check and the time you open it, your program will fail unexpectedly.

It's better to go and open the file, check for failure and if all is good then do something with the file. It's even more important with security-critical code.

Details about security and race conditions: http://www.ibm.com/developerworks/library/l-sprace.html

What is 'Currying'?

A curried function is a function of several arguments rewritten such that it accepts the first argument and returns a function that accepts the second argument and so on. This allows functions of several arguments to have some of their initial arguments partially applied.

Apache 2.4.6 on Ubuntu Server: Client denied by server configuration (PHP FPM) [While loading PHP file]

I had the following configuration in my httpd.conf that denied executing the wpadmin/setup-config.php file from wordpress. Removing the |-config part solved the problem. I think this httpd.conf is from plesk but it could be some default suggested config from wordpress, i don't know. Anyway, I could safely add it back after the setup finished.

<LocationMatch "(?i:(?:wp-config\\.bak|\\.wp-config\\.php\\.swp|(?:readme|license|changelog|-config|-sample)\\.(?:php|md|txt|htm|html)))">
                        Require all denied
                </LocationMatch>

In PHP, how do you change the key of an array element?

Easy stuff:

this function will accept the target $hash and $replacements is also a hash containing newkey=>oldkey associations.

This function will preserve original order, but could be problematic for very large (like above 10k records) arrays regarding performance & memory.

function keyRename(array $hash, array $replacements) {
    $new=array();
    foreach($hash as $k=>$v)
    {
        if($ok=array_search($k,$replacements))
            $k=$ok;
        $new[$k]=$v;
    }
    return $new;    
}

this alternative function would do the same, with far better performance & memory usage, at the cost of loosing original order (which should not be a problem since it is hashtable!)

function keyRename(array $hash, array $replacements) {

    foreach($hash as $k=>$v)
        if($ok=array_search($k,$replacements))
        {
          $hash[$ok]=$v;
          unset($hash[$k]);
        }

    return $hash;       
}

Remove characters before character "."

public string RemoveCharactersBeforeDot(string s)
{
 string splitted=s.Split('.');
 return splitted[splitted.Length-1]
}

How to filter an array of objects based on values in an inner array with jq?

Here is another solution which uses any/2

map(select(any(.Names[]; contains("data"))|not)|.Id)[]

with the sample data and the -r option it produces

cb94e7a42732b598ad18a8f27454a886c1aa8bbba6167646d8f064cd86191e2b
a4b7e6f5752d8dcb906a5901f7ab82e403b9dff4eaaeebea767a04bac4aada19

'innerText' works in IE, but not in Firefox

found this here:

<!--[if lte IE 8]>
    <script type="text/javascript">
        if (Object.defineProperty && Object.getOwnPropertyDescriptor &&
            !Object.getOwnPropertyDescriptor(Element.prototype, "textContent").get)
          (function() {
            var innerText = Object.getOwnPropertyDescriptor(Element.prototype, "innerText");
            Object.defineProperty(Element.prototype, "textContent",
              { // It won't work if you just drop in innerText.get
                // and innerText.set or the whole descriptor.
                get : function() {
                  return innerText.get.call(this)
                },
                set : function(x) {
                  return innerText.set.call(this, x)
                }
              }
            );
          })();
    </script>
<![endif]-->

Limiting the number of characters in a string, and chopping off the rest

Ideally you should try not to modify the internal data representation for the purpose of creating the table. Whats the problem with String.format()? It will return you new string with required width.

How to subtract 30 days from the current date using SQL Server

Try this:

SELECT      GETDATE(), 'Today'
UNION ALL
SELECT      DATEADD(DAY,  10, GETDATE()), '10 Days Later'
UNION ALL
SELECT      DATEADD(DAY, –10, GETDATE()), '10 Days Earlier'
UNION ALL
SELECT      DATEADD(MONTH,  1, GETDATE()), 'Next Month'
UNION ALL
SELECT      DATEADD(MONTH, –1, GETDATE()), 'Previous Month'
UNION ALL
SELECT      DATEADD(YEAR,  1, GETDATE()), 'Next Year'
UNION ALL
SELECT      DATEADD(YEAR, –1, GETDATE()), 'Previous Year'

Result Set:

———————– —————
2011-05-20 21:11:42.390 Today
2011-05-30 21:11:42.390 10 Days Later
2011-05-10 21:11:42.390 10 Days Earlier
2011-06-20 21:11:42.390 Next Month
2011-04-20 21:11:42.390 Previous Month
2012-05-20 21:11:42.390 Next Year
2010-05-20 21:11:42.390 Previous Year

Difference between a View's Padding and Margin

Padding is inside of a View.

Margin is outside of a View.

This difference may be relevant to background or size properties.

Programmatically saving image to Django ImageField

Ok, If all you need to do is associate the already existing image file path with the ImageField, then this solution may be helpfull:

from django.core.files.base import ContentFile

with open('/path/to/already/existing/file') as f:
  data = f.read()

# obj.image is the ImageField
obj.image.save('imgfilename.jpg', ContentFile(data))

Well, if be earnest, the already existing image file will not be associated with the ImageField, but the copy of this file will be created in upload_to dir as 'imgfilename.jpg' and will be associated with the ImageField.

Characters allowed in a URL

RFC3986 defines two sets of characters you can use in a URI:

  • Reserved Characters: :/?#[]@!$&'()*+,;=

    reserved = gen-delims / sub-delims

    gen-delims = ":" / "/" / "?" / "#" / "[" / "]" / "@"

    sub-delims = "!" / "$" / "&" / "'" / "(" / ")" / "*" / "+" / "," / ";" / "="

    The purpose of reserved characters is to provide a set of delimiting characters that are distinguishable from other data within a URI. URIs that differ in the replacement of a reserved character with its corresponding percent-encoded octet are not equivalent.

  • Unreserved Characters: A-Za-z0-9-_.~

    unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"

    Characters that are allowed in a URI but do not have a reserved purpose are called unreserved.

Difference between dates in JavaScript

var DateDiff = function(type, start, end) {

    let // or var
        years = end.getFullYear() - start.getFullYear(),
        monthsStart = start.getMonth(),
        monthsEnd = end.getMonth()
    ;

    var returns = -1;

    switch(type){
        case 'm': case 'mm': case 'month': case 'months':
            returns = ( ( ( years * 12 ) - ( 12 - monthsEnd ) ) + ( 12 - monthsStart ) );
            break;
        case 'y': case 'yy': case 'year': case 'years':
            returns = years;
            break;
        case 'd': case 'dd': case 'day': case 'days':
            returns = ( ( end - start ) / ( 1000 * 60 * 60 * 24 ) );
            break;
    }

    return returns;

}

Usage

var qtMonths = DateDiff('mm', new Date('2015-05-05'), new Date());

var qtYears = DateDiff('yy', new Date('2015-05-05'), new Date());

var qtDays = DateDiff('dd', new Date('2015-05-05'), new Date());

OR

var qtMonths = DateDiff('m', new Date('2015-05-05'), new Date()); // m || y || d

var qtMonths = DateDiff('month', new Date('2015-05-05'), new Date()); // month || year || day

var qtMonths = DateDiff('months', new Date('2015-05-05'), new Date()); // months || years || days

...

var DateDiff = function (type, start, end) {

    let // or var
        years = end.getFullYear() - start.getFullYear(),
        monthsStart = start.getMonth(),
        monthsEnd = end.getMonth()
    ;

    if(['m', 'mm', 'month', 'months'].includes(type)/*ES6*/)
        return ( ( ( years * 12 ) - ( 12 - monthsEnd ) ) + ( 12 - monthsStart ) );
    else if(['y', 'yy', 'year', 'years'].includes(type))
        return years;
    else if (['d', 'dd', 'day', 'days'].indexOf(type) !== -1/*EARLIER JAVASCRIPT VERSIONS*/)
        return ( ( end - start ) / ( 1000 * 60 * 60 * 24 ) );
    else
        return -1;

}

How to completely DISABLE any MOUSE CLICK

You can overlay a big, semi-transparent <div> that takes all the clicks. Just append a new <div> to <body> with this style:

.overlay {
    background-color: rgba(1, 1, 1, 0.7);
    bottom: 0;
    left: 0;
    position: fixed;
    right: 0;
    top: 0;
}

ADB.exe is obsolete and has serious performance problems

In the SDK Manager, in the SDK Tools tab, check if you have any updates, if not, deselect "Hide Obsolete Packages" and check if you have something marked as (obsolete) if so, deselect the item and apply. In my case, it was the Android SDK Tools.

C/C++ Struct vs Class

One more difference in C++, when you inherit a class from struct without any access specifier, it become public inheritance where as in case of class it's private inheritance.

Error in Python script "Expected 2D array, got 1D array instead:"?

I was facing the same issue earlier but I have somehow found the solution, You can try reg.predict([[3300]]).

The API used to allow scalar value but now you need to give a 2D array.

How can I get an int from stdio in C?

The solution is quite simple ... you're reading getchar() which gives you the first character in the input buffer, and scanf just parsed it (really don't know why) to an integer, if you just forget the getchar for a second, it will read the full buffer until a newline char.

printf("> ");
int x;
scanf("%d", &x);
printf("got the number: %d", x);

Outputs

> [prompt expecting input, lets write:] 1234 [Enter]
got the number: 1234

Difference between array_push() and $array[] =

When you call a function in PHP (such as array_push()), there are overheads to the call, as PHP has to look up the function reference, find its position in memory and execute whatever code it defines.

Using $arr[] = 'some value'; does not require a function call, and implements the addition straight into the data structure. Thus, when adding a lot of data it is a lot quicker and resource-efficient to use $arr[].

Running shell command and capturing the output

eg, execute('ls -ahl') differentiated three/four possible returns and OS platforms:

  1. no output, but run successfully
  2. output empty line, run successfully
  3. run failed
  4. output something, run successfully

function below

def execute(cmd, output=True, DEBUG_MODE=False):
"""Executes a bash command.
(cmd, output=True)
output: whether print shell output to screen, only affects screen display, does not affect returned values
return: ...regardless of output=True/False...
        returns shell output as a list with each elment is a line of string (whitespace stripped both sides) from output
        could be 
        [], ie, len()=0 --> no output;    
        [''] --> output empty line;     
        None --> error occured, see below

        if error ocurs, returns None (ie, is None), print out the error message to screen
"""
if not DEBUG_MODE:
    print "Command: " + cmd

    # https://stackoverflow.com/a/40139101/2292993
    def _execute_cmd(cmd):
        if os.name == 'nt' or platform.system() == 'Windows':
            # set stdin, out, err all to PIPE to get results (other than None) after run the Popen() instance
            p = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)
        else:
            # Use bash; the default is sh
            p = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True, executable="/bin/bash")

        # the Popen() instance starts running once instantiated (??)
        # additionally, communicate(), or poll() and wait process to terminate
        # communicate() accepts optional input as stdin to the pipe (requires setting stdin=subprocess.PIPE above), return out, err as tuple
        # if communicate(), the results are buffered in memory

        # Read stdout from subprocess until the buffer is empty !
        # if error occurs, the stdout is '', which means the below loop is essentially skipped
        # A prefix of 'b' or 'B' is ignored in Python 2; 
        # it indicates that the literal should become a bytes literal in Python 3 
        # (e.g. when code is automatically converted with 2to3).
        # return iter(p.stdout.readline, b'')
        for line in iter(p.stdout.readline, b''):
            # # Windows has \r\n, Unix has \n, Old mac has \r
            # if line not in ['','\n','\r','\r\n']: # Don't print blank lines
                yield line
        while p.poll() is None:                                                                                                                                        
            sleep(.1) #Don't waste CPU-cycles
        # Empty STDERR buffer
        err = p.stderr.read()
        if p.returncode != 0:
            # responsible for logging STDERR 
            print("Error: " + str(err))
            yield None

    out = []
    for line in _execute_cmd(cmd):
        # error did not occur earlier
        if line is not None:
            # trailing comma to avoid a newline (by print itself) being printed
            if output: print line,
            out.append(line.strip())
        else:
            # error occured earlier
            out = None
    return out
else:
    print "Simulation! The command is " + cmd
    print ""

Turn a string into a valid filename?

Just to further complicate things, you are not guaranteed to get a valid filename just by removing invalid characters. Since allowed characters differ on different filenames, a conservative approach could end up turning a valid name into an invalid one. You may want to add special handling for the cases where:

  • The string is all invalid characters (leaving you with an empty string)

  • You end up with a string with a special meaning, eg "." or ".."

  • On windows, certain device names are reserved. For instance, you can't create a file named "nul", "nul.txt" (or nul.anything in fact) The reserved names are:

    CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9

You can probably work around these issues by prepending some string to the filenames that can never result in one of these cases, and stripping invalid characters.

error LNK2038: mismatch detected for '_ITERATOR_DEBUG_LEVEL': value '0' doesn't match value '2' in main.obj

In VS2010 iterator debug level defaults to 2 in debug and is disabled in release. One of the dlls you are using probably has iterator debugging turned off in debug either because it was built in an older version of visual studio or they explicitly added the defines to the project.

Search for _ITERATOR_DEBUG_LEVEL and _SECURE_SCL remove them or set them appropriately in all projects and sources and rebuild everything.

_ITERATOR_DEBUG_LEVEL = 0 // disabled (for release builds)
_ITERATOR_DEBUG_LEVEL = 1 // enabled (if _SECURE_SCL is defined)
_ITERATOR_DEBUG_LEVEL = 2 // enabled (for debug builds)

In short you are probably mixing release and debug dlls. Don't linked release dlls in debug or vice versa!

Removing address bar from browser (to view on Android)

I found that if you add the command to unload, he keeps down the page, ie the page that move! Hope it works with you too!

window.addEventListener("load", function() { window.scrollTo(0, 1); });
window.addEventListener("unload", function() { window.scrollTo(0, 1); });

Using a 7-inch tablet with android, www.kupsoft.com visit my website and check how it behaves page, I use this command in my portal.

How to set the color of "placeholder" text?

::-webkit-input-placeholder { /* WebKit browsers */
    color:    #999;
}
:-moz-placeholder { /* Mozilla Firefox 4 to 18 */
    color:    #999;
}
::-moz-placeholder { /* Mozilla Firefox 19+ */
    color:    #999;
}
:-ms-input-placeholder { /* Internet Explorer 10+ */
    color:    #999;
}

How to fix corrupt HDFS FIles

You can use

  hdfs fsck /

to determine which files are having problems. Look through the output for missing or corrupt blocks (ignore under-replicated blocks for now). This command is really verbose especially on a large HDFS filesystem so I normally get down to the meaningful output with

  hdfs fsck / | egrep -v '^\.+$' | grep -v eplica

which ignores lines with nothing but dots and lines talking about replication.

Once you find a file that is corrupt

  hdfs fsck /path/to/corrupt/file -locations -blocks -files

Use that output to determine where blocks might live. If the file is larger than your block size it might have multiple blocks.

You can use the reported block numbers to go around to the datanodes and the namenode logs searching for the machine or machines on which the blocks lived. Try looking for filesystem errors on those machines. Missing mount points, datanode not running, file system reformatted/reprovisioned. If you can find a problem in that way and bring the block back online that file will be healthy again.

Lather rinse and repeat until all files are healthy or you exhaust all alternatives looking for the blocks.

Once you determine what happened and you cannot recover any more blocks, just use the

  hdfs fs -rm /path/to/file/with/permanently/missing/blocks

command to get your HDFS filesystem back to healthy so you can start tracking new errors as they occur.

Reading file from Workspace in Jenkins with Groovy script

Based on your comments, you would be better off with Text-finder plugin.

It allows to search file(s), as well as console, for a regular expression and then set the build either unstable or failed if found.

As for the Groovy, you can use the following to access ${WORKSPACE} environment variable:
def workspace = manager.build.getEnvVars()["WORKSPACE"]

View's SELECT contains a subquery in the FROM clause

create view view_clients_credit_usage as
    select client_id, sum(credits_used) as credits_used 
    from credit_usage 
    group by client_id

create view view_credit_status as 
    select 
        credit_orders.client_id, 
        sum(credit_orders.number_of_credits) as purchased, 
        ifnull(t1.credits_used,0) as used 
    from credit_orders
    left outer join view_clients_credit_usage as t1 on t1.client_id = credit_orders.client_id
    where credit_orders.payment_status='Paid'
    group by credit_orders.client_id)

How to find difference between two Joda-Time DateTimes in minutes

DateTime d1 = ...;
DateTime d2 = ...;
Period period = new Period(d1, d2, PeriodType.minutes());
int differenceMinutes = period.getMinutes();

In practice I think this will always give the same result as the answer based on Duration. For a different time unit than minutes, though, it might be more correct. For example there are 365 days from 2016/2/2 to 2017/2/1, but actually it's less than 1 year and should truncate to 0 years if you use PeriodType.years().

In theory the same could happen for minutes because of leap seconds, but Joda doesn't support leap seconds.

Recyclerview inside ScrollView not scrolling smoothly

Try doing:

RecyclerView v = (RecyclerView) findViewById(...);
v.setNestedScrollingEnabled(false);

As an alternative, you can modify your layout using the support design library. I guess your current layout is something like:

<ScrollView >
   <LinearLayout >

       <View > <!-- upper content -->
       <RecyclerView > <!-- with custom layoutmanager -->

   </LinearLayout >
</ScrollView >

You can modify that to:

<CoordinatorLayout >

    <AppBarLayout >
        <CollapsingToolbarLayout >
             <!-- with your content, and layout_scrollFlags="scroll" -->
        </CollapsingToolbarLayout >
    </AppBarLayout >

    <RecyclerView > <!-- with standard layoutManager -->

</CoordinatorLayout >

However this is a longer road to take, and if you are OK with the custom linear layout manager, then just disable nested scrolling on the recycler view.

Edit (4/3/2016)

The v 23.2 release of the support libraries now includes a factory “wrap content” feature in all default LayoutManagers. I didn’t test it, but you should probably prefer it to that library you were using.

<ScrollView >
   <LinearLayout >

       <View > <!-- upper content -->
       <RecyclerView > <!-- with wrap_content -->

   </LinearLayout >
</ScrollView >

UnicodeDecodeError: 'ascii' codec can't decode byte 0xef in position 1

try:

string.decode('utf-8')  # or:
unicode(string, 'utf-8')

edit:

'(\xef\xbd\xa1\xef\xbd\xa5\xcf\x89\xef\xbd\xa5\xef\xbd\xa1)\xef\xbe\x89'.decode('utf-8') gives u'(\uff61\uff65\u03c9\uff65\uff61)\uff89', which is correct.

so your problem must be at some oter place, possibly if you try to do something with it were there is an implicit conversion going on (could be printing, writing to a stream...)

to say more we'll need to see some code.

Android ListView with onClick items

listview.setOnItemClickListener(new OnItemClickListener(){

//setting onclick to items in the listview.

@Override
public void onItemClick(AdapterView<?>adapter,View v, int position){
Intent intent;
switch(position){

// case 0 is the first item in the listView.

  case 0:
    intent = new Intent(Activity.this,firstActivity.class);
    break;
//case 1 is the second item in the listView.

  case 1:
    intent = new Intent(Activity.this,secondActivity.class);
    break;
 case 2:
    intent = new Intent(Activity.this,thirdActivity.class);
    break;
//add more if you have more items in listView
startActivity(intent);
}

});

Share cookie between subdomain and domain

The 2 domains mydomain.com and subdomain.mydomain.com can only share cookies if the domain is explicitly named in the Set-Cookie header. Otherwise, the scope of the cookie is restricted to the request host. (This is referred to as a "host-only cookie". See What is a host only cookie?)

For instance, if you sent the following header from subdomain.mydomain.com, then the cookie won't be sent for requests to mydomain.com:

Set-Cookie: name=value

However if you use the following, it will be usable on both domains:

Set-Cookie: name=value; domain=mydomain.com

This cookie will be sent for any subdomain of mydomain.com, including nested subdomains like subsub.subdomain.mydomain.com.

In RFC 2109, a domain without a leading dot meant that it could not be used on subdomains, and only a leading dot (.mydomain.com) would allow it to be used across multiple subdomains (but not the top-level domain, so what you ask was not possible in the older spec).

However, all modern browsers respect the newer specification RFC 6265, and will ignore any leading dot, meaning you can use the cookie on subdomains as well as the top-level domain.

In summary, if you set a cookie like the second example above from mydomain.com, it would be accessible by subdomain.mydomain.com, and vice versa. This can also be used to allow sub1.mydomain.com and sub2.mydomain.com to share cookies.

See also:

How do I enumerate the properties of a JavaScript object?

If you are using the Underscore.js library, you can use function keys:

_.keys({one : 1, two : 2, three : 3});
=> ["one", "two", "three"]

Absolute and Flexbox in React Native

The first step would be to add

position: 'absolute',

then if you want the element full width, add

left: 0,
right: 0,

then, if you want to put the element in the bottom, add

bottom: 0,
// don't need set top: 0

if you want to position the element at the top, replace bottom: 0 by top: 0

PHP Fatal error: Cannot access empty property

To access a variable in a class, you must use $this->myVar instead of $this->$myvar.

And, you should use access identifier to declare a variable instead of var.

Please read the doc here.

flutter remove back button on appbar

The AppBar widget has a property called automaticallyImplyLeading. By default it's value is true. If you don't want flutter automatically build the back button for you then just make the property false.

appBar: AppBar(
  title: Text("YOUR_APPBAR_TITLE"), 
  automaticallyImplyLeading: false,
),

To add your custom back button

appBar: AppBar(
  title: Text("YOUR_APPBAR_TITLE"), 
  automaticallyImplyLeading: false,
  leading: YOUR_CUSTOM_WIDGET(),
),

How to parse a CSV in a Bash script?

Using awk:

export INDEX=2
export VALUE=bar

awk -F, '$'$INDEX' ~ /^'$VALUE'$/ {print}' inputfile.csv

Edit: As per Dennis Williamson's excellent comment, this could be much more cleanly (and safely) written by defining awk variables using the -v switch:

awk -F, -v index=$INDEX -v value=$VALUE '$index == value {print}' inputfile.csv

Jeez...with variables, and everything, awk is almost a real programming language...

how to do "press enter to exit" in batch

@echo off
echo somethink
echo Press enter to exit
set /p input=

tap gesture recognizer - which object was tapped?

in swift it quite simple

Write this code in ViewDidLoad() function

let tap = UITapGestureRecognizer(target: self, action: #selector(tapHandler(gesture:)))
    tap.numberOfTapsRequired = 2
    tapView.addGestureRecognizer(tap)

The Handler Part this could be in viewDidLoad or outside the viewDidLoad, batter is put in extension

@objc func tapHandler(gesture: UITapGestureRecognizer) {
    currentGestureStates.text = "Double Tap"
} 

here i'm just testing the code by printing the output if you want to make an action you can do whatever you want or more practise and read

Can't find out where does a node.js app running and can't kill it

You can kill all node processes using pkill node

or you can do a ps T to see all processes on this terminal
then you can kill a specific process ID doing a kill [processID] example: kill 24491

Additionally, you can do a ps -help to see all the available options

Get the value of checked checkbox?

<input class="messageCheckbox" type="checkbox" onchange="getValue(this.value)" value="3" name="mailId[]">

<input class="messageCheckbox" type="checkbox" onchange="getValue(this.value)" value="1" name="mailId[]">
function getValue(value){
    alert(value);
}

Django: List field in model?

I think it will help you.

from django.db import models
import ast

class ListField(models.TextField):
    __metaclass__ = models.SubfieldBase
    description = "Stores a python list"

    def __init__(self, *args, **kwargs):
        super(ListField, self).__init__(*args, **kwargs)

    def to_python(self, value):
        if not value:
            value = []

        if isinstance(value, list):
            return value

        return ast.literal_eval(value)

    def get_prep_value(self, value):
        if value is None:
            return value

        return unicode(value)

    def value_to_string(self, obj):
        value = self._get_val_from_obj(obj)
        return self.get_db_prep_value(value)

class ListModel(models.Model):
    test_list = ListField()

Example :

>>> ListModel.objects.create(test_list= [[1,2,3], [2,3,4,4]])

>>> ListModel.objects.get(id=1)

>>> o = ListModel.objects.get(id=1)
>>> o.id
1L
>>> o.test_list
[[1, 2, 3], [2, 3, 4, 4]]
>>> 

`getchar()` gives the same output as the input string

According to the definition of getchar(), it reads a character from the standard input. Unfortunately stdin is mistaken for keyboard which might not be the case for getchar. getchar uses a buffer as stdin and reads a single character at a time. In your case since there is no EOF, the getchar and putchar are running multiple times and it looks to you as it the whole string is being printed out at a time. Make a small change and you will understand:

putchar(c);
printf("\n");     
c = getchar();

Now look at the output compared to the original code.

Another example that will explain you the concept of getchar and buffered stdin :

void main(){
int c;
printf("Enter character");
c = getchar();
putchar();
c = getchar();
putchar();
}

Enter two characters in the first case. The second time when getchar is running are you entering any character? NO but still putchar works.

This ultimately means there is a buffer and when ever you are typing something and click enter this goes and settles in the buffer. getchar uses this buffer as stdin.

What's the location of the JavaFX runtime JAR file, jfxrt.jar, on Linux?

The location of jfxrt.jar in JDK 1.8 (Windows) is:

C:\Program Files\Java\jdk1.8.0_05\jre\lib\ext\jfxrt.jar

Builder Pattern in Effective Java

Once you've got an idea, in practice, you may find lombok's @Builder much more convenient.

@Builder lets you automatically produce the code required to have your class be instantiable with code such as:

Person.builder()
  .name("Adam Savage")
  .city("San Francisco")
  .job("Mythbusters")
  .job("Unchained Reaction")
 .build(); 

Official documentation: https://www.projectlombok.org/features/Builder

Why do I need 'b' to encode a string with Base64?

If the string is Unicode the easiest way is:

import base64                                                        

a = base64.b64encode(bytes(u'complex string: ñáéíóúÑ', "utf-8"))

# a: b'Y29tcGxleCBzdHJpbmc6IMOxw6HDqcOtw7PDusOR'

b = base64.b64decode(a).decode("utf-8", "ignore")                    

print(b)
# b :complex string: ñáéíóúÑ

How do I pass a value from a child back to the parent form?

The fastest and more flexible way to do that is passing the parent to the children from the constructor as below:

  1. Declare a property in the parent form:

    public string MyProperty {get; set;}

  2. Declare a property from the parent in child form:

    private ParentForm ParentProperty {get; set;}

  3. Write the child's constructor like this:

      public ChildForm(ParentForm parent){
          ParentProperty= parent;
      }
    
  4. Change the value of the parent property everywhere in the child form:

    ParentProperty.MyProperty = "New value";

It's done. the property MyProperty in the parent form is changed. With this solution, you can change multiple properties from the child form. So delicious, no?!

PHP - remove all non-numeric characters from a string

You can use preg_replace in this case;

$res = preg_replace("/[^0-9]/", "", "Every 6 Months" );

$res return 6 in this case.

If want also to include decimal separator or thousand separator check this example:

$res = preg_replace("/[^0-9.]/", "", "$ 123.099");

$res returns "123.099" in this case

Include period as decimal separator or thousand separator: "/[^0-9.]/"

Include coma as decimal separator or thousand separator: "/[^0-9,]/"

Include period and coma as decimal separator and thousand separator: "/[^0-9,.]/"

Parsing HTML using Python

I recommend lxml for parsing HTML. See "Parsing HTML" (on the lxml site).

In my experience Beautiful Soup messes up on some complex HTML. I believe that is because Beautiful Soup is not a parser, rather a very good string analyzer.

What is the garbage collector in Java?

Garbage Collector is part of JRE that makes sure that object that are not referenced will be freed from memory.
It usually runs when you app runs out of memory. AFAIK it holds a graph that represents the links between the objects and isolated objects can be freed.
To save performance the current objects grouped into generations, each time GC scans an object and finds that it is still referenced its generation count incremented by 1 (to some max maximum value, 3 or 4 i think) , and the new generation are scanned first (the shortest the object in memory the more probably it is no longer needed) so not all objects being scanned every time GC run.
read this for more information.

How to check for an undefined or null variable in JavaScript?

Since there is no single complete and correct answer, I will try to summarize:

In general, the expression:

if (typeof(variable) != "undefined" && variable != null)

cannot be simplified, because the variable might be undeclared so omitting the typeof(variable) != "undefined" would result in ReferenceError. But, you can simplify the expression according to the context:

If the variable is global, you can simplify to:

if (window.variable != null)

If it is local, you can probably avoid situations when this variable is undeclared, and also simplify to:

if (variable != null)

If it is object property, you don't have to worry about ReferenceError:

if (obj.property != null)

Check if a property exists in a class

If you are binding like I was:

<%# Container.DataItem.GetType().GetProperty("Property1") != null ? DataBinder.Eval(Container.DataItem, "Property1") : DataBinder.Eval(Container.DataItem, "Property2")  %>

Python json.loads shows ValueError: Extra data

As you can see in the following example, json.loads (and json.load) does not decode multiple json object.

>>> json.loads('{}')
{}
>>> json.loads('{}{}') # == json.loads(json.dumps({}) + json.dumps({}))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Python27\lib\json\__init__.py", line 338, in loads
    return _default_decoder.decode(s)
  File "C:\Python27\lib\json\decoder.py", line 368, in decode
    raise ValueError(errmsg("Extra data", s, end, len(s)))
ValueError: Extra data: line 1 column 3 - line 1 column 5 (char 2 - 4)

If you want to dump multiple dictionaries, wrap them in a list, dump the list (instead of dumping dictionaries multiple times)

>>> dict1 = {}
>>> dict2 = {}
>>> json.dumps([dict1, dict2])
'[{}, {}]'
>>> json.loads(json.dumps([dict1, dict2]))
[{}, {}]

Defining an abstract class without any abstract methods

You can, the question in my mind is more should you. Right from the beginning, I'll say that there is no hard and fast answer. Do the right thing for your current situation.

To me inheritance implies an 'is-a' relationship. Imagine a dog class, which can be extended by more specialized sub types (Alsatian, Poodle, etc). In this case making the dog class abstract may be the right thing to do since sub-types are dogs. Now let's imagine that dogs need a collar. In this case inheritance doesn't make sense: it's nonsense to have a 'is-a' relationship between dogs and collars. This is definitely a 'has-a' relationship, collar is a collaborating object. Making collar abstract just so that dogs can have one doesn't make sense.

I often find that abstract classes with no abstract methods are really expressing a 'has-a' relationship. In these cases I usually find that the code can be better factored without using inheritance. I also find that abstract classes with no abstract method are often a code smell and at the very least should lead to questions being raised in a code review.

Again, this is entirely subjective. There may well be situations when an abstract class with no abstract methods makes sense, it's entirely up to interpretation and justification. Make the best decision for whatever you're working on.

Creating and throwing new exception

To call a specific exception such as FileNotFoundException use this format

if (-not (Test-Path $file)) 
{
    throw [System.IO.FileNotFoundException] "$file not found."
}

To throw a general exception use the throw command followed by a string.

throw "Error trying to do a task"

When used inside a catch, you can provide additional information about what triggered the error

How to iterate over a std::map full of strings in C++

iter->first and iter->second are variables, you are attempting to call them as methods.

Could not find or load main class with a Jar File

This error comes even if you miss "-" by mistake before the word jar

Wrong command java jar test.jar

Correct command java -jar test.jar

How can I see the size of files and directories in linux?

go to specific directory then run below command

# du -sh * 

4.0K    1
4.0K    anadb.sh --> Shell file
4.0K    db.sh/    --> shell file
24K     backup4/  --> Directory
8.0K    backup6/  --> Directory 
1.9G    backup.sql.gz  --> sql file

Testing web application on Mac/Safari when I don't own a Mac

Unfortunately you cannot run MacOS X on anything but a genuine Mac.

MacOS X Server however can be run in VMWare. A stopgap solution would be to install it inside a VM. But you should be aware that MacOS X Server and MacOS X are not exactly the same, and your testing is not going to be exactly what the user has. Not to mention the $499 price tag.

Simplest way is to buy yourself a cheap mac mini or a laptop with a broken screen used on ebay, plug it onto your network and access it via VNC to do your testing.

Environment variable in Jenkins Pipeline

You can access the same environment variables from groovy using the same names (e.g. JOB_NAME or env.JOB_NAME).

From the documentation:

Environment variables are accessible from Groovy code as env.VARNAME or simply as VARNAME. You can write to such properties as well (only using the env. prefix):

env.MYTOOL_VERSION = '1.33'
node {
  sh '/usr/local/mytool-$MYTOOL_VERSION/bin/start'
}

These definitions will also be available via the REST API during the build or after its completion, and from upstream Pipeline builds using the build step.

For the rest of the documentation, click the "Pipeline Syntax" link from any Pipeline job enter image description here

Changing SQL Server collation to case insensitive from case sensitive?

You can do that but the changes will affect for new data that is inserted on the database. On the long run follow as suggested above.

Also there are certain tricks you can override the collation, such as parameters for stored procedures or functions, alias data types, and variables are assigned the default collation of the database. To change the collation of an alias type, you must drop the alias and re-create it.

You can override the default collation of a literal string by using the COLLATE clause. If you do not specify a collation, the literal is assigned the database default collation. You can use DATABASEPROPERTYEX to find the current collation of the database.

You can override the server, database, or column collation by specifying a collation in the ORDER BY clause of a SELECT statement.

Accessing a property in a parent Component

On Angular 6, I access parent properties by injecting the parent via constructor. Not the best solution but it works:

 constructor(@Optional() public parentComponentInjectionObject: ParentComponent){
    // And access like this:
    parentComponentInjectionObject.thePropertyYouWantToAccess;
}

Is Python strongly typed?

TLDR;

Python typing is Dynamic so you can change a string variable to an int

x = 'somestring'
x = 50

Python typing is Strong so you can't merge types:

'foo' + 3 --> TypeError: cannot concatenate 'str' and 'int' objects

In weakly-typed Javascript this happens...

 'foo'+3 = 'foo3'

Regarding Type Inference

Java forces you to explicitly declare your object types

int x = 50;

Kotlin uses inference to realize it's an int

x = 50

But because both languages use static types, x can't be changed from an int. Neither language would allow a dynamic change like

x = 50
x = 'now a string'

How do I set up NSZombieEnabled in Xcode 4?

I find this alternative more convenient:

  1. Click the "Run Button Dropdown"
  2. From the list choose Profile
  3. The program "Instruments" should open where you can also choose Zombies
  4. Now you can interact with your app and try to cause the error
  5. As soon as the error happens you should get a hint on when your object was released and therefore deallocated.

Zombies

As soon as a zombie is detected you then get a neat "Zombie Stack" that shows you when the object in question was allocated and where it was retained or released:

Event Type    RefCt     Responsible Caller
Malloc            1     -[MyViewController loadData:]
Retain            2     -[MyDataManager initWithBaseURL:]
Release           1     -[MyDataManager initWithBaseURL:]
Release           0     -[MyViewController loadData:]
Zombie           -1     -[MyService prepareURLReuqest]

Advantages compared to using the diagnostic tab of the Xcode Schemes:

  1. If you forget to uncheck the option in the diagnostic tab there no objects will be released from memory.

  2. You get a more detailed stack that shows you in what methods your corrupt object was allocated / released or retained.

how to specify local modules as npm package dependencies

I couldn't find a neat way in the end so I went for create a directory called local_modules and then added this bashscript to the package.json in scripts->preinstall

#!/bin/sh
for i in $(find ./local_modules -type d -maxdepth 1) ; do
    packageJson="${i}/package.json"
    if [ -f "${packageJson}" ]; then
        echo "installing ${i}..."
        npm install "${i}"
    fi
done

Disabled form fields not submitting data

Use the CSS pointer-events:none on fields you want to "disable" (possibly together with a greyed background) which allows the POST action, like:

<input type="text" class="disable">

.disable{
pointer-events:none;
background:grey;
}

Ref: https://developer.mozilla.org/en-US/docs/Web/CSS/pointer-events

Rails :include vs. :joins

'joins' just used to join tables and when you called associations on joins then it will again fire query (it mean many query will fire)

lets suppose you have tow model, User and Organisation
User has_many organisations
suppose you have 10 organisation for a user 
@records= User.joins(:organisations).where("organisations.user_id = 1")
QUERY will be 
 select * from users INNER JOIN organisations ON organisations.user_id = users.id where organisations.user_id = 1

it will return all records of organisation related to user
and @records.map{|u|u.organisation.name}
it run QUERY like 
select * from organisations where organisations.id = x then time(hwo many organisation you have)

total number of SQL is 11 in this case

But with 'includes' will eager load the included associations and add them in memory(load all associations on first load) and not fire query again

when you get records with includes like @records= User.includes(:organisations).where("organisations.user_id = 1") then query will be

select * from users INNER JOIN organisations ON organisations.user_id = users.id where organisations.user_id = 1
and 


 select * from organisations where organisations.id IN(IDS of organisation(1, to 10)) if 10 organisation
and when you run this 

@records.map{|u|u.organisation.name} no query will fire