Programs & Examples On #Itemsource

Single controller with multiple GET methods in ASP.NET Web API

In ASP.NET Core 2.0 you can add Route attribute to the controller:

public class SomeController : Controller
    public SomeValue GetItems(CustomParam parameter) { ... }

    public SomeValue GetChildItems(CustomParam parameter, SomeObject parent) { ... }

How do I print an IFrame from javascript in Safari/Chrome

You can use


Work at Chrome!

How can I delete a service in Windows?

If they are .NET created services you can use the installutil.exe with the /u switch its in the .net framework folder like C:\Windows\Microsoft.NET\Framework64\v2.0.50727

SQL to Query text in access with an apostrophe in it

How about more simply: Select * from tblStudents where [name] = replace(YourName,"'","''")

How to set the JSTL variable value in javascript?

Just don't. Don't write code with code. Write a JSON object or a var somewhere but for the love of a sensible HTTP divide, don't write JavaScript functions or methods hardcoded with vars/properties provided by JSTL. Generating JSON is cool. It ends there or your UI dev hates you.

Imagine if you had to dig into JavaScript to find something that was setting parameters in the middle of a class that originated on the client-side. It's awful. Pass data back and forth. Handle the data. But don't try to generate actual code.

What's the difference between lists and tuples?

Difference between list and tuple

Tuples and lists are both seemingly similar sequence types in Python.

  1. Literal syntax

    We use parenthesis () to construct tuples and square brackets [ ] to get a new list. Also, we can use call of the appropriate type to get required structure — tuple or list.

    someTuple = (4,6)
    someList  = [2,6] 
  2. Mutability

    Tuples are immutable, while lists are mutable. This point is the base the for the following ones.

  3. Memory usage

    Due to mutability, you need more memory for lists and less memory for tuples.

  4. Extending

    You can add a new element to both tuples and lists with the only difference that the id of the tuple will be changed (i.e., we’ll have a new object).

  5. Hashing

    Tuples are hashable and lists are not. It means that you can use a tuple as a key in a dictionary. The list can't be used as a key in a dictionary, whereas a tuple can be used

    tup      = (1,2)
    list_    = [1,2] 
    c = {tup   : 1}     # ok
    c = {list_ : 1}     # error
  6. Semantics

    This point is more about best practice. You should use tuples as heterogeneous data structures, while lists are homogenous sequences.

ASP.NET - How to write some html in the page? With Response.Write?

You can go with the literal control of or you can use panels or the purpose.

Append to the end of a Char array in C++

If you are not allowed to use C++'s string class (which is terrible teaching C++ imho), a raw, safe array version would look something like this.

#include <cstring>
#include <iostream>

int main()
    char array1[] ="The dog jumps ";
    char array2[] = "over the log";
    char * newArray = new char[std::strlen(array1)+std::strlen(array2)+1];
    std::cout << newArray << std::endl;
    delete [] newArray;
    return 0;

This assures you have enough space in the array you're doing the concatenation to, without assuming some predefined MAX_SIZE. The only requirement is that your strings are null-terminated, which is usually the case unless you're doing some weird fixed-size string hacking.

Edit, a safe version with the "enough buffer space" assumption:

#include <cstring>
#include <iostream>

int main()
    const unsigned BUFFER_SIZE = 50;
    char array1[BUFFER_SIZE];
    std::strncpy(array1, "The dog jumps ", BUFFER_SIZE-1); //-1 for null-termination
    char array2[] = "over the log";
    std::strncat(array1,array2,BUFFER_SIZE-strlen(array1)-1); //-1 for null-termination
    std::cout << array1 << std::endl;
    return 0;

Which is the correct C# infinite loop, for (;;) or while (true)?

The original K&R book for C, from which C# can trace its ancestry, recommended

for (;;) ...

for infinite loops. It's unambiguous, easy to read, and has a long and noble history behind it.

Addendum (Feb 2017)

Of course, if you think that this looping form (or any other form) is too cryptic, you can always just add a comment.

// Infinite loop
for (;;)


for (;;)    // Loop forever

Android button font size


Button bt = new Button(this);

In xml:


Declare and assign multiple string variables at the same time


string     Camnr , Klantnr , Ordernr , Bonnr , Volgnr , Omschrijving , Startdatum ,    Bonprioriteit , Matsoort , Dikte , Draaibaarheid , Draaiomschrijving , Orderleverdatum , Regeltaakkode , Gebruiksvoorkeur , Regelcamprog , Regeltijd , Orderrelease ;

and then

Camnr = Klantnr = Ordernr = Bonnr = Volgnr = Omschrijving = Startdatum = Bonprioriteit = Matsoort = Dikte = Draaibaarheid = Draaiomschrijving = Orderleverdatum = Regeltaakkode = Gebruiksvoorkeur = Regelcamprog = Regeltijd = Orderrelease = "";

How to insert a new line in Linux shell script?

You could use the printf(1) command, e.g. like

printf "Hello times %d\nHere\n" $[2+3] 

The  printf command may accept arguments and needs a format control string similar (but not exactly the same) to the one for the standard C printf(3) function...

Terminal Multiplexer for Microsoft Windows - Installers for GNU Screen or tmux

Adding to the thread, there's a new console in town called babun, im running tmux in it without a problem. lets you run bash or the zsh.

click here for github

Eclipse 3.5 Unable to install plugins

Its the Windows OS that make the problem. I got the same problem. Then I tried some other app which use JavaVM to connect the internet, and they fails. Try update JRE, you will notice it. If JRE cannot update itself, then there is some socket inaccessibility that prevent internet access apart from using native windows API. I reinstall Win7 and it fixed the problem.

Safest way to get last record ID from a table


You can use one of these examples:




But the first one will be more efficient because no index scan is needed (if you have index on Id column).

The second one solution is equivalent to the third (both of them need to scan table to get max id).

dropping infinite values from dataframes in pandas?

The above solution will modify the infs that are not in the target columns. To remedy that,

lst = [np.inf, -np.inf]
to_replace = {v: lst for v in ['col1', 'col2']}
df.replace(to_replace, np.nan)

How to add button in ActionBar(Android)?

An activity populates the ActionBar in its onCreateOptionsMenu() method.

Instead of using setcustomview(), just override onCreateOptionsMenu like this:

public boolean onCreateOptionsMenu(Menu menu) {
  MenuInflater inflater = getMenuInflater();
  inflater.inflate(, menu);
  return true;

If an actions in the ActionBar is selected, the onOptionsItemSelected() method is called. It receives the selected action as parameter. Based on this information you code can decide what to do for example:

public boolean onOptionsItemSelected(MenuItem item) {
  switch (item.getItemId()) {
      Toast.makeText(this, "Menu Item 1 selected", Toast.LENGTH_SHORT).show();
      Toast.makeText(this, "Menu item 2 selected", Toast.LENGTH_SHORT).show();
  return true;

Removing duplicate objects with Underscore for Javascript

here's my solution (coffeescript) :

  deepUniq: (coll) ->
    result = []
    remove_first_el_duplicates = (coll2) ->

      rest =
      first = _.first(coll2)
      result.push first
      equalsFirst = (el) -> _.isEqual(el,first)

      newColl = _.reject rest, equalsFirst

      unless _.isEmpty newColl
        remove_first_el_duplicates newColl



_.deepUniq([ {a:1,b:12}, [ 2, 1, 2, 1 ], [ 1, 2, 1, 2 ],[ 2, 1, 2, 1 ], {a:1,b:12} ]) 
//=> [ { a: 1, b: 12 }, [ 2, 1, 2, 1 ], [ 1, 2, 1, 2 ] ]

Change x axes scale in matplotlib

This is not so much an answer to your original question as to one of the queries you had in the body of your question.

A little preamble, so that my naming doesn't seem strange:

import matplotlib
from matplotlib import rc
from matplotlib.figure import Figure
ax = self.figure.add_subplot( 111 )

As has been mentioned you can use ticklabel_format to specify that matplotlib should use scientific notation for large or small values:


You can affect the way that this is displayed using the flags in rcParams (from matplotlib import rcParams) or by setting them directly. I haven't found a more elegant way of changing between '1e' and 'x10^' scientific notation than:

ax.xaxis.major.formatter._useMathText = True

This should give you the more Matlab-esc, and indeed arguably better appearance. I think the following should do the same:

rc('text', usetex=True)

Add Header and Footer for PDF using iTextsharp

The answers to this question, while they are correct, are very unnecessarily complicated. It doesn't take that much code for text to show up in the header/footer. Here is a simple example of adding text to the header/footer.

The current version of iTextSharp works by implementing a callback class which is defined by the IPdfPageEvent interface. From what I understand, it's not a good idea to add things during the OnStartPage method, so instead I will be using the OnEndPage page method. The events are triggered depending on what is happening to the PdfWriter

First, create a class which implements IPdfPageEvent. In the:

public void OnEndPage(PdfWriter writer, Document document)

function, obtain the PdfContentByte object by calling

PdfContentByte cb = writer.DirectContent;

Now you can add text very easily:

ColumnText ct = new ColumnText(cb);

cb.SetFontAndSize(BaseFont.CreateFont(BaseFont.TIMES_ROMAN, BaseFont.CP1252, BaseFont.NOT_EMBEDDED), 12.0f);
//Note, (0,0) in this case is at the bottom of the document
cb.SetTextMatrix(document.LeftMargin, document.BottomMargin); 
cb.ShowText(String.Format("{0} {1}", "Testing Text", "Like this"));

So the full for the OnEndPage function will be:

public void OnEndPage(PdfWriter writer, Document document)
    PdfContentByte cb = writer.DirectContent;
    ColumnText ct = new ColumnText(cb);

    cb.SetFontAndSize(BaseFont.CreateFont(BaseFont.TIMES_ROMAN, BaseFont.CP1252, BaseFont.NOT_EMBEDDED), 12.0f);
    cb.SetTextMatrix(document.LeftMargin, document.BottomMargin);
    cb.ShowText(String.Format("{0} {1}", "Testing Text", "Like this"));


This will show up at the bottom of your document. One last thing. Don't forget to assign the IPdfPageEvent like this:

writter.PageEvent = new PDFEvents();

To the PdfWriter writter object

For the header it is very similar. Just flip the SetTextMatrix y coordinate:

cb.SetTextMatrix(document.LeftMargin, document.PageSize.Height - document.TopMargin);

How to catch an Exception from a thread

Exception handling in Thread : By default run() method doesn’t throw any exception, so all checked exceptions inside the run method has to be caught and handled there only and for runtime exceptions we can use UncaughtExceptionHandler. UncaughtExceptionHandler is an interface provided by Java to handle exceptions in a Thread run method. So we can implement this interface and set back our implementing class back to Thread object using setUncaughtExceptionHandler() method. But this handler has to be set before we call start() on the tread.

if we don’t set uncaughtExceptionHandler then the Threads ThreadGroup acts as a handler.

 public class FirstThread extends Thread {

int count = 0;

public void run() {
    while (true) {
        System.out.println("FirstThread doing something urgent, count : "
                + (count++));
        throw new RuntimeException();


public static void main(String[] args) {
    FirstThread t1 = new FirstThread();
    t1.setUncaughtExceptionHandler(new UncaughtExceptionHandler() {
        public void uncaughtException(Thread t, Throwable e) {
            System.out.printf("Exception thrown by %s with id : %d",
                    t.getName(), t.getId());

Nice explanation given at

Latex - Change margins of only a few pages

Use the "geometry" package and write \newgeometry{left=3cm,bottom=0.1cm} where you want to change your margins. When you want to reset your margins, you write \restoregeometry.

How to directly move camera to current location in Google Maps Android API v2?

The above answer is not according to what Google Doc Referred for Location Tracking in Google api v2.

I just followed the official tutorial and ended up with this class that is fetching the current location and centring the map on it as soon as i get that.

you can extend this class to have LocationReciever to have periodic Location Update. I just executed this code on api level 7

Here it goes.

import android.content.Intent;
import android.content.IntentSender;
import android.location.Location;
import android.os.Bundle;
import android.util.Log;
import android.widget.Toast;


public class MainActivity extends FragmentActivity implements 

private SupportMapFragment mapFragment;
private GoogleMap map;
private LocationClient mLocationClient;
 * Define a request code to send to Google Play services
 * This code is returned in Activity.onActivityResult
private final static int CONNECTION_FAILURE_RESOLUTION_REQUEST = 9000;

// Define a DialogFragment that displays the error dialog
public static class ErrorDialogFragment extends DialogFragment {

    // Global field to contain the error dialog
    private Dialog mDialog;

    // Default constructor. Sets the dialog field to null
    public ErrorDialogFragment() {
        mDialog = null;

    // Set the dialog to display
    public void setDialog(Dialog dialog) {
        mDialog = dialog;

    // Return a Dialog to the DialogFragment.
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        return mDialog;

protected void onCreate(Bundle savedInstanceState) {

    mLocationClient = new LocationClient(this, this, this);

    mapFragment = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(;
    map = mapFragment.getMap();



 * Called when the Activity becomes visible.
protected void onStart() {
    // Connect the client.


 * Called when the Activity is no longer visible.
protected void onStop() {
    // Disconnecting the client invalidates it.

 * Handle results returned to the FragmentActivity
 * by Google Play services
protected void onActivityResult(
                int requestCode, int resultCode, Intent data) {
    // Decide what to do based on the original request code
    switch (requestCode) {

             * If the result code is Activity.RESULT_OK, try
             * to connect again
            switch (resultCode) {
                case Activity.RESULT_OK:


private boolean isGooglePlayServicesAvailable() {
    // Check that Google Play services is available
    int resultCode =  GooglePlayServicesUtil.isGooglePlayServicesAvailable(this);
    // If Google Play services is available
    if (ConnectionResult.SUCCESS == resultCode) {
        // In debug mode, log the status
        Log.d("Location Updates", "Google Play services is available.");
        return true;
    } else {
        // Get the error dialog from Google Play services
        Dialog errorDialog = GooglePlayServicesUtil.getErrorDialog( resultCode,

        // If Google Play services can provide an error dialog
        if (errorDialog != null) {
            // Create a new DialogFragment for the error dialog
            ErrorDialogFragment errorFragment = new ErrorDialogFragment();
  , "Location Updates");

        return false;

 * Called by Location Services when the request to connect the
 * client finishes successfully. At this point, you can
 * request the current location or start periodic updates
public void onConnected(Bundle dataBundle) {
    // Display the connection status
    Toast.makeText(this, "Connected", Toast.LENGTH_SHORT).show();
    Location location = mLocationClient.getLastLocation();
    LatLng latLng = new LatLng(location.getLatitude(), location.getLongitude());
    CameraUpdate cameraUpdate = CameraUpdateFactory.newLatLngZoom(latLng, 17);

 * Called by Location Services if the connection to the
 * location client drops because of an error.
public void onDisconnected() {
    // Display the connection status
    Toast.makeText(this, "Disconnected. Please re-connect.",

 * Called by Location Services if the attempt to
 * Location Services fails.
public void onConnectionFailed(ConnectionResult connectionResult) {
     * Google Play services can resolve some errors it detects.
     * If the error has a resolution, try sending an Intent to
     * start a Google Play services activity that can resolve
     * error.
    if (connectionResult.hasResolution()) {
        try {
            // Start an Activity that tries to resolve the error
            * Thrown if Google Play services canceled the original
            * PendingIntent
        } catch (IntentSender.SendIntentException e) {
            // Log the error
    } else {
       Toast.makeText(getApplicationContext(), "Sorry. Location services not available to you", Toast.LENGTH_LONG).show();


How to "grep" for a filename instead of the contents of a file?

You can find the relative path of a file using tree, just pipe the output to grep to filter down

tree -f | grep filename

Here is a function you can put into your .bash_profile, .bashrc, .zshrc or other...

findfile(){ tree -f | grep $1; } # $1 = filename, -f is full path

VB.NET 'If' statement with 'Or' conditional has both sides evaluated?

It's your "fault" in that that's how Or is defined, so it's the behaviour you should expect:

In a Boolean comparison, the Or operator always evaluates both expressions, which could include making procedure calls. The OrElse Operator (Visual Basic) performs short-circuiting, which means that if expression1 is True, then expression2 is not evaluated.

But you don't have to endure it. You can use OrElse to get short-circuiting behaviour.

So you probably want:

If (example Is Nothing OrElse Not example.Item = compare.Item) Then
End If

I can't say it reads terribly nicely, but it should work...

Android: How to Programmatically set the size of a Layout

LinearLayout YOUR_LinearLayout =(LinearLayout)findViewById(
    LinearLayout.LayoutParams param = new LinearLayout.LayoutParams(
                       /*width*/ ViewGroup.LayoutParams.MATCH_PARENT,
               /*height*/ 100,
               /*weight*/ 1.0f

Login failed for user 'IIS APPPOOL\ASP.NET v4.0'

I hate the ApplicationPoolIdentity. I always set a Windows User Account as the account on AppPools.

As adrift says, it does sound like a database security issue. So create an NT user account, assign it to the ASP.NET v4.0 AppPool and then grant it permission on the website folder and to the relevant table(s) in SQL.

Adding a Button to a WPF DataGrid


<DataGrid x:Name="dgv_Students" AutoGenerateColumns="False"  ItemsSource="{Binding People}" Margin="10,20,10,0" Style="{StaticResource AzureDataGrid}" FontFamily="B Yekan" Background="#FFB9D1BA" >
                                <Button Click="Button_Click_dgvs">Text</Button>

Code Behind :

       private IEnumerable<DataGridRow> GetDataGridRowsForButtons(DataGrid grid)
{ //IQueryable 
    var itemsSource = grid.ItemsSource as IEnumerable;
    if (null == itemsSource) yield return null;
    foreach (var item in itemsSource)
        var row = grid.ItemContainerGenerator.ContainerFromItem(item) as DataGridRow;
        if (null != row & row.IsSelected) yield return row;

void Button_Click_dgvs(object sender, RoutedEventArgs e)

    for (var vis = sender as Visual; vis != null; vis = VisualTreeHelper.GetParent(vis) as Visual)
        if (vis is DataGridRow)
           // var row = (DataGrid)vis;

            var rows = GetDataGridRowsForButtons(dgv_Students);
            string id;
            foreach (DataGridRow dr in rows)
                id = (dr.Item as tbl_student).Identification_code;

After clicking on the Button, the ID of that row is returned to you and you can use it for your Button name.

Adding a tooltip to an input box

<input type="name" placeholder="First Name" title="First Name" />

title="First Name" solves my proble. it worked with bootstrap.

How to search file text for a pattern and replace it with a given value

Keep in mind that, when you do this, the filesystem could be out of space and you may create a zero-length file. This is catastrophic if you're doing something like writing out /etc/passwd files as part of system configuration management.

Note that in-place file editing like in the accepted answer will always truncate the file and write out the new file sequentially. There will always be a race condition where concurrent readers will see a truncated file. If the process is aborted for any reason (ctrl-c, OOM killer, system crash, power outage, etc) during the write then the truncated file will also be left over, which can be catastrophic. This is the kind of dataloss scenario which developers MUST consider because it will happen. For that reason, I think the accepted answer should most likely not be the accepted answer. At a bare minimum write to a tempfile and move/rename the file into place like the "simple" solution at the end of this answer.

You need to use an algorithm that:

  1. Reads the old file and writes out to the new file. (You need to be careful about slurping entire files into memory).

  2. Explicitly closes the new temporary file, which is where you may throw an exception because the file buffers cannot be written to disk because there is no space. (Catch this and cleanup the temporary file if you like, but you need to rethrow something or fail fairly hard at this point.

  3. Fixes the file permissions and modes on the new file.

  4. Renames the new file and drops it into place.

With ext3 filesystems you are guaranteed that the metadata write to move the file into place will not get rearranged by the filesystem and written before the data buffers for the new file are written, so this should either succeed or fail. The ext4 filesystem has also been patched to support this kind of behavior. If you are very paranoid you should call the fdatasync() system call as a step 3.5 before moving the file into place.

Regardless of language, this is best practice. In languages where calling close() does not throw an exception (Perl or C) you must explicitly check the return of close() and throw an exception if it fails.

The suggestion above to simply slurp the file into memory, manipulate it and write it out to the file will be guaranteed to produce zero-length files on a full filesystem. You need to always use to move a fully-written temporary file into place.

A final consideration is the placement of the temporary file. If you open a file in /tmp then you have to consider a few problems:

  • If /tmp is mounted on a different file system you may run /tmp out of space before you've written out the file that would otherwise be deployable to the destination of the old file.

  • Probably more importantly, when you try to mv the file across a device mount you will transparently get converted to cp behavior. The old file will be opened, the old files inode will be preserved and reopened and the file contents will be copied. This is most likely not what you want, and you may run into "text file busy" errors if you try to edit the contents of a running file. This also defeats the purpose of using the filesystem mv commands and you may run the destination filesystem out of space with only a partially written file.

    This also has nothing to do with Ruby's implementation. The system mv and cp commands behave similarly.

What is more preferable is to open a Tempfile in the same directory as the old file. This ensures that there will be no cross-device move issues. The mv itself should never fail, and you should always get a complete and untruncated file. Any failures, such as device out of space, permission errors, etc., should be encountered during writing the Tempfile out.

The only downsides to the approach of creating the Tempfile in the destination directory are:

  • Sometimes you may not be able to open a Tempfile there, such as if you are trying to 'edit' a file in /proc for example. For that reason you might want to fall back and try /tmp if opening the file in the destination directory fails.
  • You must have enough space on the destination partition in order to hold both the complete old file and the new file. However, if you have insufficient space to hold both copies then you are probably short on disk space and the actual risk of writing a truncated file is much higher, so I would argue this is a very poor tradeoff outside of some exceedingly narrow (and well-monitored) edge cases.

Here's some code that implements the full-algorithm (windows code is untested and unfinished):

#!/usr/bin/env ruby

require 'tempfile'

def file_edit(filename, regexp, replacement)
  tempdir = File.dirname(filename)
  tempprefix = File.basename(filename)
  tempprefix.prepend('.') unless RUBY_PLATFORM =~ /mswin|mingw|windows/
  tempfile =
    begin, tempdir)
    end do |line|
    tempfile.puts line.gsub(regexp, replacement)
  tempfile.fdatasync unless RUBY_PLATFORM =~ /mswin|mingw|windows/
  unless RUBY_PLATFORM =~ /mswin|mingw|windows/
    stat = File.stat(filename)
    FileUtils.chown stat.uid, stat.gid, tempfile.path
    FileUtils.chmod stat.mode, tempfile.path
    # FIXME: apply perms on windows
  end tempfile.path, filename

file_edit('/tmp/foo', /foo/, "baz")

And here is a slightly tighter version that doesn't worry about every possible edge case (if you are on Unix and don't care about writing to /proc):

#!/usr/bin/env ruby

require 'tempfile'

def file_edit(filename, regexp, replacement)".#{File.basename(filename)}", File.dirname(filename)) do |tempfile| do |line|
      tempfile.puts line.gsub(regexp, replacement)
    stat = File.stat(filename)
    FileUtils.chown stat.uid, stat.gid, tempfile.path
    FileUtils.chmod stat.mode, tempfile.path tempfile.path, filename

file_edit('/tmp/foo', /foo/, "baz")

The really simple use-case, for when you don't care about file system permissions (either you're not running as root, or you're running as root and the file is root owned):

#!/usr/bin/env ruby

require 'tempfile'

def file_edit(filename, regexp, replacement)".#{File.basename(filename)}", File.dirname(filename)) do |tempfile| do |line|
      tempfile.puts line.gsub(regexp, replacement)
    tempfile.close tempfile.path, filename

file_edit('/tmp/foo', /foo/, "baz")

TL;DR: That should be used instead of the accepted answer at a minimum, in all cases, in order to ensure the update is atomic and concurrent readers will not see truncated files. As I mentioned above, creating the Tempfile in the same directory as the edited file is important here to avoid cross device mv operations being translated into cp operations if /tmp is mounted on a different device. Calling fdatasync is an added layer of paranoia, but it will incur a performance hit, so I omitted it from this example since it is not commonly practiced.

Test for non-zero length string in Bash: [ -n "$var" ] or [ "$var" ]

It is better to use the more powerful [[ as far as Bash is concerned.

Usual cases

if [[ $var ]]; then   # var is set and it is not empty
if [[ ! $var ]]; then # var is not set or it is set to an empty string

The above two constructs look clean and readable. They should suffice in most cases.

Note that we don't need to quote the variable expansions inside [[ as there is no danger of word splitting and globbing.

To prevent shellcheck's soft complaints about [[ $var ]] and [[ ! $var ]], we could use the -n option.

Rare cases

In the rare case of us having to make a distinction between "being set to an empty string" vs "not being set at all", we could use these:

if [[ ${var+x} ]]; then           # var is set but it could be empty
if [[ ! ${var+x} ]]; then         # var is not set
if [[ ${var+x} && ! $var ]]; then # var is set and is empty

We can also use the -v test:

if [[ -v var ]]; then             # var is set but it could be empty
if [[ ! -v var ]]; then           # var is not set
if [[ -v var && ! $var ]]; then   # var is set and is empty
if [[ -v var && -z $var ]]; then  # var is set and is empty

Related posts and documentation

There are a plenty of posts related to this topic. Here are a few:

What is the difference between Python and IPython?

ipython is an interactive shell built with python.

From the project website:

IPython provides a rich toolkit to help you make the most out of using Python, with:

  • Powerful Python shells (terminal and Qt-based).
  • A web-based notebook with the same core features but support for code, text, mathematical expressions, inline plots and other rich media.
  • Support for interactive data visualization and use of GUI toolkits.
  • Flexible, embeddable interpreters to load into your own projects.
  • Easy to use, high performance tools for parallel computing.

Note that the first 2 lines tell you it helps you make the most of using Python. Thus, you don't need to alter your code, the IPython shell runs your python code just like the normal python shell does, only with more features.

I recommend reading the IPython tutorial to get a sense of what features you gain when using IPython.

How to use Regular Expressions (Regex) in Microsoft Excel both in-cell and loops

I don't want to have to enable a reference library as I need my scripts to be portable. The Dim foo As New VBScript_RegExp_55.RegExp line caused User Defined Type Not Defined errors, but I found a solution that worked for me.

Update RE comments w/ @chrisneilsen :

I was under the impression that enabling a reference library was tied to the local computers settings, but it is in fact, tied directly to the workbook. So, you can enable a reference library, share a macro enabled workbook and the end user wouldn't have to enable the library as well. Caveat: The advantage to Late Binding is that the developer does not have to worry about the wrong version of an object library being installed on the user's computer. This likely would not be an issue w/ the VBScript_RegExp_55.RegExp library, but I'm not sold that the "performance" benifit is worth it for me at this time, as we are talking imperceptible milliseconds in my code. I felt this deserved an update to help others understand. If you enable the reference library, you can use "early bind", but if you don't, as far as I can tell, the code will work fine, but you need to "late bind" and loose on some performance/debugging features.


What you'll want to do is put an example string in cell A1, then test your strPattern. Once that's working adjust then rng as desired.

Public Sub RegExSearch()
    Dim regexp As Object
    'Dim regex As New VBScript_RegExp_55.regexp 'Caused "User Defined Type Not Defined" Error
    Dim rng As Range, rcell As Range
    Dim strInput As String, strPattern As String
    Set regexp = CreateObject("vbscript.regexp")
    Set rng = ActiveSheet.Range("A1:A1")
    strPattern = "([a-z]{2})([0-9]{8})"
    'Search for 2 Letters then 8 Digits Eg: XY12345678 = Matched

    With regexp
        .Global = False
        .MultiLine = False
        .ignoreCase = True
        .Pattern = strPattern
    End With

    For Each rcell In rng.Cells

        If strPattern <> "" Then
            strInput = rcell.Value

            If regexp.test(strInput) Then
                MsgBox rcell & " Matched in Cell " & rcell.Address
                MsgBox "No Matches!"
            End If
        End If
End Sub

Why am I getting Unknown error in line 1 of pom.xml?

You must to upgrade the m2e connector. It's a known bug, but there is a solution:

  1. Into Eclipse click "Help" > "Install new Software..."

  2. Appears a window. In the "Install" window:

    2a. Into the input box "Work with", enter next site location and press Enter

    2b. Appears a lot of information into "Name" input Box. Select all the items

    2c. Click "Next" Button.

Finish the installation and restart Eclipse.

How can I build a recursive function in python?

Recursion in Python works just as recursion in an other language, with the recursive construct defined in terms of itself:

For example a recursive class could be a binary tree (or any tree):

class tree():
    def __init__(self):
        '''Initialise the tree'''
        self.Data = None
        self.Count = 0
        self.LeftSubtree = None
        self.RightSubtree = None

    def Insert(self, data):
        '''Add an item of data to the tree'''
        if self.Data == None:
            self.Data = data
            self.Count += 1
        elif data < self.Data:
            if self.LeftSubtree == None:
                # tree is a recurive class definition
                self.LeftSubtree = tree()
            # Insert is a recursive function
        elif data == self.Data:
            self.Count += 1
        elif data > self.Data:
            if self.RightSubtree == None:
                self.RightSubtree = tree()

if __name__ == '__main__':
    T = tree()
    # The root node
    # Will be put into the left subtree
    # Will be put into the right subtree

As already mentioned a recursive structure must have a termination condition. In this class, it is not so obvious because it only recurses if new elements are added, and only does it a single time extra.

Also worth noting, python by default has a limit to the depth of recursion available, to avoid absorbing all of the computer's memory. On my computer this is 1000. I don't know if this changes depending on hardware, etc. To see yours :

import sys

and to set it :

import sys #(if you haven't already)

edit: I can't guarentee that my binary tree is the most efficient design ever. If anyone can improve it, I'd be happy to hear how

What's the difference between emulation and simulation?

Please forgive me if I'm wrong. And I have to admit upfront that I haven't done any research on these 2 terms. Anyway...

Emulation is to mimic something with detailed known results, whatever the internal behaviors actually are. We only try to get things done and don't care much about what goes on inside.

Simulation, on the other hand, is to mimic something with some known behaviors to study something not being known yet.

my 2cents

How can I align two divs horizontally?

Add a class to each of the divs:

.source, .destination {_x000D_
    float: left;_x000D_
    width: 48%;_x000D_
    margin: 0;_x000D_
    padding: 0;_x000D_
.source {_x000D_
    margin-right: 4%;_x000D_
<div class="source">_x000D_
    <span>source list</span>_x000D_
    <select size="10">_x000D_
        <option />_x000D_
        <option />_x000D_
        <option />_x000D_
<div class="destination">_x000D_
    <span>destination list</span>_x000D_
    <select size="10">_x000D_
        <option />_x000D_
        <option />_x000D_
        <option />_x000D_

That's a generic percentages solution - using pixel-based widths is usually much more reliable. You'll probably want to change the various margin/padding sizes too.

You can also optionally wrap the HTML in a container div, and use this CSS:

.container {
  overflow: hidden;

This will ensure subsequent content does not wrap around the floated elements.

Can't install laravel installer via composer

I am using WSL with ubuntu 16.04 LTS version with php 7.3 and laravel 5.7

sudo apt-get install php7.3-zip

Work for me

Is there a no-duplicate List implementation out there?

The documentation for collection interfaces says:

Set — a collection that cannot contain duplicate elements.
List — an ordered collection (sometimes called a sequence). Lists can contain duplicate elements.

So if you don't want duplicates, you probably shouldn't use a list.

Java integer list

To insert a sleep command you can use Thread.sleep(2000). So the code would be:

List<Integer> myCoords = new ArrayList<Integer>();
Iterator<Integer> myListIterator = someList.iterator(); 
while (myListIterator.hasNext()) {
    Integer coord =;    

This would output: 10 20 30 40 50

If you want the numbers after each other you could use: System.out.print(coord +" " ); and if you want to repeat the section you can put it in another while loop.

List<Integer> myCoords = new ArrayList<Integer>();
    Iterator<Integer> myListIterator = someList.iterator(); 
    while (myListIterator.hasNext()) {
        Integer coord =;    
        System.out.print(coord + " ");

This would output: 10 20 30 40 50 10 20 30 40 50 ... and never stop until you kill the program.

Edit: You do have to put the sleep command in a try catch block

Comparison of C++ unit test frameworks

See this question for some discussion.

They recommend the articles: Exploring the C++ Unit Testing Framework Jungle, By Noel Llopis. And the more recent: C++ Test Unit Frameworks

I have not found an article that compares googletest to the other frameworks yet.

PHP check whether property exists in object or class

Neither isset or property_exists work for me.

  • isset returns false if the property exists but is NULL.
  • property_exists returns true if the property is part of the object's class definition, even if it has been unset.

I ended up going with:

    $exists = array_key_exists($property, get_object_vars($obj));


    class Foo {
        public $bar;

        function __construct() {
            $property = 'bar';

            isset($this->$property); // FALSE
            property_exists($this, $property); // TRUE
            array_key_exists($property, get_object_vars($this)); // TRUE


            isset($this->$property); // FALSE
            property_exists($this, $property); // TRUE
            array_key_exists($property, get_object_vars($this)); // FALSE

            $this->$property = 'baz';

            isset($this->$property); // TRUE
            property_exists($this, $property); // TRUE
            array_key_exists($property, get_object_vars($this));  // TRUE

Handling Enter Key in Vue.js

Event Modifiers

You can refer to event modifiers in vuejs to prevent form submission on enter key.

It is a very common need to call event.preventDefault() or event.stopPropagation() inside event handlers.

Although we can do this easily inside methods, it would be better if the methods can be purely about data logic rather than having to deal with DOM event details.

To address this problem, Vue provides event modifiers for v-on. Recall that modifiers are directive postfixes denoted by a dot.

<form v-on:submit.prevent="<method>">

As the documentation states, this is syntactical sugar for e.preventDefault() and will stop the unwanted form submission on press of enter key.

Here is a working fiddle.

new Vue({_x000D_
  el: '#myApp',_x000D_
  data: {_x000D_
    emailAddress: '',_x000D_
    log: ''_x000D_
  methods: {_x000D_
    validateEmailAddress: function(e) {_x000D_
      if (e.keyCode === 13) {_x000D_
        alert('Enter was pressed');_x000D_
      } else if (e.keyCode === 50) {_x000D_
        alert('@ was pressed');_x000D_
      }      _x000D_
      this.log += e.key;_x000D_
    postEmailAddress: function() {_x000D_
   this.log += '\n\nPosting';_x000D_
    noop () {_x000D_
      // do nothing ?_x000D_
html, body, #editor {_x000D_
  margin: 0;_x000D_
  height: 100%;_x000D_
  color: #333;_x000D_
<script src="[email protected]/dist/vue.js"></script>_x000D_
<div id="myApp" style="padding:2rem; background-color:#fff;">_x000D_
<form v-on:submit.prevent="noop">_x000D_
  <input type="text" v-model="emailAddress" v-on:keyup="validateEmailAddress" />_x000D_
  <button type="button" v-on:click="postEmailAddress" >Subscribe</button> _x000D_
  <br /><br />_x000D_
  <textarea v-model="log" rows="4"></textarea>  _x000D_

Vue.js - How to properly watch for nested data

VueJs deep watch in child objects

new Vue({
    el: "#myElement",
    data: {
        entity: {
            properties: []
    watch: {
        '': {
            handler: function (after, before) {
                // Changes detected. Do work...     
            deep: true

Height of status bar in Android

Toggled Fullscreen Solution:

This solution may look like a workaround, but it actually accounts for whether your app is fullscreen (aka hiding the status bar) or not:

Display display = getWindowManager().getDefaultDisplay();
Point size = new Point(); display.getSize(size);
int barheight = size.y - findViewById(;

This way, if your app is currently fullscreen, barheight will equal 0.

Personally I had to use this to correct absolute TouchEvent coordinates to account for the status bar as so:

public boolean onTouch(View view,MotionEvent event) {
    Display display = getWindowManager().getDefaultDisplay();
    Point size = new Point(); display.getSize(size);
    int YCoord = (int)event.getRawY() - size.y + rootView.getHeight());

And that will get the absolute y-coordinate whether the app be fullscreen or not.


When and how should I use a ThreadLocal variable?

Since Java 8 release, there is more declarative way to initialize ThreadLocal:

ThreadLocal<Cipher> local = ThreadLocal.withInitial(() -> "init value");

Until Java 8 release you had to do the following:

ThreadLocal<String> local = new ThreadLocal<String>(){
    protected String initialValue() {
        return "init value";

Moreover, if instantiation method (constructor, factory method) of class that is used for ThreadLocal does not take any parameters, you can simply use method references (introduced in Java 8):

class NotThreadSafe {
    // no parameters
    public NotThreadSafe(){}

ThreadLocal<NotThreadSafe> container = ThreadLocal.withInitial(NotThreadSafe::new);

Note: Evaluation is lazy since you are passing java.util.function.Supplier lambda that is evaluated only when ThreadLocal#get is called but value was not previously evaluated.

Redirection of standard and error output appending to the same log file

Like Unix shells, PowerShell supports > redirects with most of the variations known from Unix, including 2>&1 (though weirdly, order doesn't matter - 2>&1 > file works just like the normal > file 2>&1).

Like most modern Unix shells, PowerShell also has a shortcut for redirecting both standard error and standard output to the same device, though unlike other redirection shortcuts that follow pretty much the Unix convention, the capture all shortcut uses a new sigil and is written like so: *>.

So your implementation might be:

& myjob.bat *>> $logfile

Where can I download Spring Framework jars without using Maven?

Please edit to keep this list of mirrors current

I found this maven repo where you could download from directly a zip file containing all the jars you need.

Alternate solution: Maven

The solution I prefer is using Maven, it is easy and you don't have to download each jar alone. You can do it with the following steps:

  1. Create an empty folder anywhere with any name you prefer, for example spring-source

  2. Create a new file named pom.xml

  3. Copy the xml below into this file

  4. Open the spring-source folder in your console

  5. Run mvn install

  6. After download finished, you'll find spring jars in /spring-source/target/dependencies

    <project xmlns="" xmlns:xsi="" xsi:schemaLocation="">

Also, if you need to download any other spring project, just copy the dependency configuration from its corresponding web page.

For example, if you want to download Spring Web Flow jars, go to its web page, and add its dependency configuration to the pom.xml dependencies, then run mvn install again.


How to make a website secured with https

What kind of business data? Trade secrets or just stuff that they don't want people to see but if it got out, it wouldn't be a big deal? If we are talking trade secrets, financial information, customer information and stuff that's generally confidential. Then don't even go down that route.

I'm wondering whether I need to use a secured connection (https) or just the forms authentication is enough.

Use a secure connection all the way.

Do I need to alter the code / Config

Yes. Well may be not. You may want to have an expert do this for you.

Is SSL and https one and the same...

Mostly yes. People usually refer to those things as the same thing.

Do I need to apply with someone to get some license or something.

You probably want to have your certificate signed by a certificate authority. It will cost you or your client a bit of money.

Do I need to make all my pages secured or only the login page...

Use https throughout. Performance is usually not an issue if the site is meant for internal users.

I was searching Internet for answer, but I was not able to get all these points... Any whitepaper or other references would also be helpful...

Start here for some pointers:

Note that SSL is a minuscule piece of making your web site secure once it is accessible from the internet. It does not prevent most sort of hacking.

Remove carriage return from string


vbcrlf = environment.newline...

Dim MyString As String = "This is a Test" & Environment.NewLine & " This is the second line!"

Dim MyNewString As String = MyString.Replace(Environment.NewLine,String.Empty)

Test if a variable is a list or tuple

If you just need to know if you can use the foo[123] notation with the variable, you can check for the existence of a __getitem__ attribute (which is what python calls when you access by index) with hasattr(foo, '__getitem__')

How to play only the audio of a Youtube video using HTML 5?

// YouTube video ID
var videoID = "CMNry4PE93Y";

// Fetch video info (using a proxy to avoid CORS errors)
fetch('' + "" + videoID).then(response => {
  if (response.ok) {
    response.text().then(ytData => {
      // parse response to find audio info
      var ytData = parse_str(ytData);
      var getAdaptiveFormats = JSON.parse(ytData.player_response).streamingData.adaptiveFormats;
      var findAudioInfo = getAdaptiveFormats.findIndex(obj => obj.audioQuality);
      // get the URL for the audio file
      var audioURL = getAdaptiveFormats[findAudioInfo].url;
      // update the <audio> element src
      var youtubeAudio = document.getElementById('youtube');
      youtubeAudio.src = audioURL;

function parse_str(str) {
  return str.split('&').reduce(function(params, param) {
    var paramSplit = param.split('=').map(function(value) {
      return decodeURIComponent(value.replace('+', ' '));
    params[paramSplit[0]] = paramSplit[1];
    return params;
  }, {});
<audio id="youtube" controls></audio>

How to "add existing frameworks" in Xcode 4?

I would like to point out that if you can't find "Link Binaries With Libraries" in your build phases tab click the "Add build phase" button in the lower right corner.

Recommended way to save uploaded files in a servlet application

Store it anywhere in an accessible location except of the IDE's project folder aka the server's deploy folder, for reasons mentioned in the answer to Uploaded image only available after refreshing the page:

  1. Changes in the IDE's project folder does not immediately get reflected in the server's work folder. There's kind of a background job in the IDE which takes care that the server's work folder get synced with last updates (this is in IDE terms called "publishing"). This is the main cause of the problem you're seeing.

  2. In real world code there are circumstances where storing uploaded files in the webapp's deploy folder will not work at all. Some servers do (either by default or by configuration) not expand the deployed WAR file into the local disk file system, but instead fully in the memory. You can't create new files in the memory without basically editing the deployed WAR file and redeploying it.

  3. Even when the server expands the deployed WAR file into the local disk file system, all newly created files will get lost on a redeploy or even a simple restart, simply because those new files are not part of the original WAR file.

It really doesn't matter to me or anyone else where exactly on the local disk file system it will be saved, as long as you do not ever use getRealPath() method. Using that method is in any case alarming.

The path to the storage location can in turn be definied in many ways. You have to do it all by yourself. Perhaps this is where your confusion is caused because you somehow expected that the server does that all automagically. Please note that @MultipartConfig(location) does not specify the final upload destination, but the temporary storage location for the case file size exceeds memory storage threshold.

So, the path to the final storage location can be definied in either of the following ways:

  • Hardcoded:

      File uploads = new File("/path/to/uploads");
  • Environment variable via SET UPLOAD_LOCATION=/path/to/uploads:

      File uploads = new File(System.getenv("UPLOAD_LOCATION"));
  • VM argument during server startup via -Dupload.location="/path/to/uploads":

      File uploads = new File(System.getProperty("upload.location"));
  • *.properties file entry as upload.location=/path/to/uploads:

      File uploads = new File(properties.getProperty("upload.location"));
  • web.xml <context-param> with name upload.location and value /path/to/uploads:

      File uploads = new File(getServletContext().getInitParameter("upload.location"));
  • If any, use the server-provided location, e.g. in JBoss AS/WildFly:

      File uploads = new File(System.getProperty(""), "uploads");

Either way, you can easily reference and save the file as follows:

File file = new File(uploads, "somefilename.ext");

try (InputStream input = part.getInputStream()) {
    Files.copy(input, file.toPath());

Or, when you want to autogenerate an unique file name to prevent users from overwriting existing files with coincidentally the same name:

File file = File.createTempFile("somefilename-", ".ext", uploads);

try (InputStream input = part.getInputStream()) {
    Files.copy(input, file.toPath(), StandardCopyOption.REPLACE_EXISTING);

How to obtain part in JSP/Servlet is answered in How to upload files to server using JSP/Servlet? and how to obtain part in JSF is answered in How to upload file using JSF 2.2 <h:inputFile>? Where is the saved File?

Note: do not use Part#write() as it interprets the path relative to the temporary storage location defined in @MultipartConfig(location).

See also:

Going from MM/DD/YYYY to DD-MMM-YYYY in java

final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd-MM-yyyy");
LocalDate localDate =;
System.out.println("Formatted Date: " + formatter.format(localDate));

Java 8 LocalDate

How to change style of a default EditText

I solved the same issue 10 minutes ago, so I will give you a short effective fix: Place this inside the application tag or your manifest:


Also set the Theme of your XML layout to Holo, in the layout's graphical view.

Libraries will be useful if you need to change more complicated theme stuff, but this little fix will work, so you can move on with your app.

How to write to the Output window in Visual Studio?

Use the OutputDebugString function or the TRACE macro (MFC) which lets you do printf-style formatting:

int x = 1;
int y = 16;
float z = 32.0;
TRACE( "This is a TRACE statement\n" );    
TRACE( "The value of x is %d\n", x );
TRACE( "x = %d and y = %d\n", x, y );
TRACE( "x = %d and y = %x and z = %f\n", x, y, z );

For-loop vs while loop in R

And about timing:

fn1 <- function (N) {
    for(i in as.numeric(1:N)) { y <- i*i }
fn2 <- function (N) {
    while (i <= N) {
        y <- i*i
        i <- i + 1

# user  system elapsed 
# 0.06    0.00    0.07 
# user  system elapsed 
# 0.12    0.00    0.13

And now we know that for-loop is faster than while-loop. You cannot ignore warnings during timing.

Format number as percent in MS SQL Server

took the challenge to solve this issue. comment number 5 (M.Ali) asked for --"The required answer is 97.36 % (not 0.97 %) .." so for that i'm attaching a photo who compare between post number 3 (sqluser) to my solution. (i'm using the postgre_sql on a mac)

enter image description here

Correct way to push into state array

You can use .concat method to create copy of your array with new data:

this.setState({ myArray: this.state.myArray.concat('new value') })

But beware of special behaviour of .concat method when passing arrays - [1, 2].concat(['foo', 3], 'bar') will result in [1, 2, 'foo', 3, 'bar'].

Java: Get first item from a collection

In java 8:

Optional<String> firstElement =;

For older versions of java, there is a getFirst method in Guava Iterables:

Iterables.getFirst(iterable, defaultValue)

Visual Studio "Could not copy" .... during build

The fastest way is changing the Build configuration type and return to previous configuration again.

Why did Servlet.service() for servlet jsp throw this exception?

If your project is Maven-based, remember to set scope to provided for such dependencies as servlet-api, jsp-api. Otherwise, these jars will be exported to WEB-INF/lib and hence contaminate with those in Tomcat server. That causes painful problems.


Set default syntax to different filetype in Sublime Text 2

In the current version of Sublime Text 2 (Build: 2139), you can set the syntax for all files of a certain file extension using an option in the menu bar. Open a file with the extension you want to set a default for and navigate through the following menus: View -> Syntax -> Open all with current extension as... ->[your syntax choice].

Updated 2012-06-28: Recent builds of Sublime Text 2 (at least since Build 2181) have allowed the syntax to be set by clicking the current syntax type in the lower right corner of the window. This will open the syntax selection menu with the option to Open all with current extension as... at the top of the menu.

Updated 2016-04-19: As of now, this also works for Sublime Text 3.

GCC fatal error: stdio.h: No such file or directory

Mac OS Mojave

The accepted answer no longer works. When running the command xcode-select --install it tells you to use "Software Update" to install updates.

In this link is the updated method:

Open a Terminal and then:

cd /Library/Developer/CommandLineTools/Packages/
open macOS_SDK_headers_for_macOS_10.14.pkg

This will open an installation Wizard.

Update 12/2019

After updating to Mojave 10.15.1 it seems that using xcode-select --install works as intended.

Validation for 10 digit mobile number and focus input field on invalid

for email validation, <input type="email"> is enough..

for mobile no use pattern attribute for input as follows:

<input type="number" pattern="\d{3}[\-]\d{3}[\-]\d{4}" required>

you can check for more patterns on

for focusing on field, you can use onkeyup() event as:

function check()

    var mobile = document.getElementById('mobile');
    var message = document.getElementById('message');

   var goodColor = "#0C6";
    var badColor = "#FF9B37";
       = badColor; = badColor;
        message.innerHTML = "required 10 digits, match requested format!"

and your HTML code should be:

<input name="mobile"  id="mobile" type="number" required onkeyup="check(); return false;" ><span id="message"></span>

Difference between parameter and argument

Generally, the parameters are what are used inside the function and the arguments are the values passed when the function is called. (Unless you take the opposite view — Wikipedia mentions alternative conventions when discussing parameters and arguments).

double sqrt(double x)
    return x;

void other(void)
     double two = sqrt(2.0);

Under my thesis, x is the parameter to sqrt() and 2.0 is the argument.

The terms are often used at least somewhat interchangeably.

What is the difference between String and string in C#?

string is an alias (or shorthand) of System.String. That means, by typing string we meant System.String. You can read more in think link: 'string' is an alias/shorthand of System.String.

How to add manifest permission to an application?

I am late but i want to complete the answer.

An permission is added in manifest.xml like

<uses-permission android:name="android.permission.INTERNET"/>

This is enough for standard permissions where no permission is prompted to the user. However, it is not enough to add permission only to manifest if it is a dangerous permission. See android doc. Like Camera, Storage permissions.

<uses-permission android:name="android.permission.CAMERA"/>

You will need to ask permission from user. I use RxPermission library that is widely used library for asking permission. Because it is long code which we have to write to ask permission.

RxPermissions rxPermissions = new RxPermissions(this); // where this is an Activity instance // Must be done during an initialization phase like onCreate
    .subscribe(granted -> {
        if (granted) { // Always true pre-M
           // I can control the camera now
        } else {
           // Oups permission denied

Add this library to your app

allprojects {
    repositories {
        maven { url '' }

dependencies {
    implementation 'com.github.tbruyelle:rxpermissions:0.10.1'
    implementation 'com.jakewharton.rxbinding2:rxbinding:2.1.1'

How to add element in Python to the end of list using list.insert?

You'll have to pass the new ordinal position to insert using len in this case:

In [62]:

[1, 2, 3, 4, 5]

git rebase merge conflict

If you have a lot of commits to rebase, and some part of them are giving conflicts, that really hurts. But I can suggest a less-known approach how to "squash all the conflicts".

First, checkout temp branch and start standard merge

git checkout -b temp
git merge origin/master

You will have to resolve conflicts, but only once and only real ones. Then stage all files and finish merge.

git commit -m "Merge branch 'origin/master' into 'temp'"

Then return to your branch (let it be alpha) and start rebase, but with automatical resolving any conflicts.

git checkout alpha
git rebase origin/master -X theirs

Branch has been rebased, but project is probably in invalid state. That's OK, we have one final step. We just need to restore project state, so it will be exact as on branch 'temp'. Technically we just need to copy its tree (folder state) via low-level command git commit-tree. Plus merging into current branch just created commit.

git merge --ff $(git commit-tree temp^{tree} -m "Fix after rebase" -p HEAD)

And delete temporary branch

git branch -D temp

That's all. We did a rebase via hidden merge.

Also I wrote a script, so that can be done in a dialog manner, you can find it here.

When do you use Git rebase instead of Git merge?

It's simple. With rebase you say to use another branch as the new base for your work.

If you have, for example, a branch master, you create a branch to implement a new feature, and say you name it cool-feature, of course the master branch is the base for your new feature.

Now at a certain point you want to add the new feature you implemented in the master branch. You could just switch to master and merge the cool-feature branch:

$ git checkout master
$ git merge cool-feature

But this way a new dummy commit is added. If you want to avoid spaghetti-history you can rebase:

$ git checkout cool-feature
$ git rebase master

And then merge it in master:

$ git checkout master
$ git merge cool-feature

This time, since the topic branch has the same commits of master plus the commits with the new feature, the merge will be just a fast-forward.

Maven: how to override the dependency added by a library

Alternatively, you can just exclude the dependency that you don't want. STAX is included in JDK 1.6, so if you're using 1.6 you can just exclude it entirely.

My example below is slightly wrong for you - you only need one of the two exclusions but I'm not quite sure which one. There are other versions of Stax floating about, in my example below I was importing A which imported B which imported C & D which each (through yet more transitive dependencies) imported different versions of Stax. So in my dependency on 'A', I excluded both versions of Stax.

    <!--  STAX comes with Java 1.6 -->

How to send a pdf file directly to the printer using JavaScript?

a function to house the print trigger...

function printTrigger(elementId) {
    var getMyFrame = document.getElementById(elementId);

an button to give the user access...

(an onClick on an a or button or input or whatever you wish)

<input type="button" value="Print" onclick="printTrigger('iFramePdf');" />
an iframe pointing to your PDF...

<iframe id="iFramePdf" src="myPdfUrl.pdf" style="dispaly:none;"></iframe>

More :

Biggest differences of Thrift vs Protocol Buffers?

I think most of these points have missed the basic fact that Thrift is an RPC framework, which happens to have the ability to serialize data using a variety of methods (binary, XML, etc).

Protocol Buffers are designed purely for serialization, it's not a framework like Thrift.

Adding VirtualHost fails: Access Forbidden Error 403 (XAMPP) (Windows 7)

I am using xampp 1.7.3. Using inspiration from here: xampp 1.7.3 upgrade broken virtual hosts access forbidden

INSTEAD OF add <Directory> .. </Directory> in httpd-vhosts.conf, I add it in httpd.conf right after <Directory "D:/xampplite/cgi-bin"> .. </Directory>.

Here is what I add in httpd.conf:

<Directory "D:/CofeeShop">
    AllowOverride All
    Options  All
    Order allow,deny
    Allow from all

And here is what I add in httpd-vhosts.conf

<VirtualHost *:8001>
    ServerAdmin [email protected]
    DocumentRoot "D:/CofeeShop"
    ServerName localhost:8001

I also add Listen 8001 in httpd.conf to complete my setting.

Hope it helps

Caching a jquery ajax response in javascript/browser

        function getDatas() {
            let cacheKey = 'memories';

            if (cacheKey in localStorage) {
                let datas = JSON.parse(localStorage.getItem(cacheKey));

                // if expired
                if (datas['expires'] < {

                } else {
            } else {
                    "dataType": "json",
                    "success": function(datas, textStatus, jqXHR) {
                        let today = new Date();

                        datas['expires'] = today.setDate(today.getDate() + 7) // expires in next 7 days


                        localStorage.setItem(cacheKey, JSON.stringify(datas));
                    "url": "http://localhost/phunsanit/snippets/PHP/json.json_encode.php",

        function setDatas(datas) {
            // display json as text

            // your code here


        // call

enter link description here

How to cd into a directory with space in the name?


cd "Documents and Photos"

problem solved.

The reason I'm submitting this answer is you'll find that StackOverflow is being used by every day users (not just web devs, programmers or power users) and this was the number one result for a simple Windows user question on Google.

People are becoming more tech-savvy, but aren't necessarily familiar with command line in the cases above.

How to get primary key of table?

I've got it, finally!


function mysql_get_prim_key($table){
$sql = "SHOW INDEX FROM $table WHERE Key_name = 'PRIMARY'";
$gp = mysql_query($sql);
$cgp = mysql_num_rows($gp);
if($cgp > 0){
// Note I'm not using a while loop because I never use more than one prim key column
$agp = mysql_fetch_array($gp);


How to convert date to timestamp?

this refactored code will do it

let toTimestamp = strDate => Date.parse(strDate)

this works on all modern browsers except ie8-

What's the difference between a method and a function?

If you feel like reading here is "My introduction to OO methods"

The idea behind Object Oriented paradigm is to "threat" the software is composed of .. well "objects". Objects in real world have properties, for instance if you have an Employee, the employee has a name, an employee id, a position, he belongs to a department etc. etc.

The object also know how to deal with its attributes and perform some operations on them. Let say if we want to know what an employee is doing right now we would ask him.

employe whatAreYouDoing.

That "whatAreYouDoing" is a "message" sent to the object. The object knows how to answer to that questions, it is said it has a "method" to resolve the question.

So, the way objects have to expose its behavior are called methods. Methods thus are the artifact object have to "do" something.

Other possible methods are

employee whatIsYourName
employee whatIsYourDepartmentsName


Functions in the other hand are ways a programming language has to compute some data, for instance you might have the function addValues( 8 , 8 ) that returns 16

// pseudo-code
function addValues( int x, int y )  return x + y 
// call it 
result = addValues( 8,8 )
print result // output is 16...

Since first popular programming languages ( such as fortran, c, pascal ) didn't cover the OO paradigm, they only call to these artifacts "functions".

for instance the previous function in C would be:

int addValues( int x, int y ) 
   return x + y;

It is not "natural" to say an object has a "function" to perform some action, because functions are more related to mathematical stuff while an Employee has little mathematic on it, but you can have methods that do exactly the same as functions, for instance in Java this would be the equivalent addValues function.

public static int addValues( int x, int y ) {
    return x + y;

Looks familiar? That´s because Java have its roots on C++ and C++ on C.

At the end is just a concept, in implementation they might look the same, but in the OO documentation these are called method.

Here´s an example of the previously Employee object in Java.

public class Employee {

    Department department;
    String name;

    public String whatsYourName(){
    public String whatsYourDeparmentsName(){
    public String whatAreYouDoing(){
        return "nothing";
    // Ignore the following, only set here for completness
    public Employee( String name ) { = name;


// Usage sample.
Employee employee = new Employee( "John" ); // Creates an employee called John

// If I want to display what is this employee doing I could use its methods.
// to know it.
String name = employee.whatIsYourName():
String doingWhat = employee.whatAreYouDoint();

// Print the info to the console.

 System.out.printf("Employee %s is doing: %s", name, doingWhat );

Employee John is doing nothing.

The difference then, is on the "domain" where it is applied.

AppleScript have the idea of "natural language" matphor , that at some point OO had. For instance Smalltalk. I hope it may be reasonable easier for you to understand methods in objects after reading this.

NOTE: The code is not to be compiled, just to serve as an example. Feel free to modify the post and add Python example.

android: how to change layout on button click?

It is very simple, just do this:

t4.setOnClickListener(new OnClickListener(){

        public void onClick(View v) {

            launchQuiz2();          // TODO Auto-generated method stub


        private void launchQuiz2() {
            Intent i = new Intent(MainActivity.this, Quiz2.class);
            // TODO Auto-generated method stub



JFrame: How to disable window resizing?

You can use this.setResizable(false); or frameObject.setResizable(false);

Escape curly brace '{' in String.Format

Use double braces {{ or }} so your code becomes:

sb.AppendLine(String.Format("public {0} {1} {{ get; private set; }}", 
prop.Type, prop.Name));

// For prop.Type of "Foo" and prop.Name of "Bar", the result would be:
// public Foo Bar { get; private set; }

How do I remove the non-numeric character from a string in java?

One more approach for removing all non-numeric characters from a string:

String newString = oldString.replaceAll("[^0-9]", "");

How to remove focus from single editText

Just find another view and give it focus instead.

var refresher = FindViewById<MvxSwipeRefreshLayout>(Resource.Id.refresher);


Automatic prune with Git fetch or pull

Since git 1.8.5 (Q4 2013):

"git fetch" (hence "git pull" as well) learned to check "fetch.prune" and "remote.*.prune" configuration variables and to behave as if the "--prune" command line option was given.

That means that, if you set remote.origin.prune to true:

git config remote.origin.prune true

Any git fetch or git pull will automatically prune.

Note: Git 2.12 (Q1 2017) will fix a bug related to this configuration, which would make git remote rename misbehave.
See "How do I rename a git remote?".

See more at commit 737c5a9:

Without "git fetch --prune", remote-tracking branches for a branch the other side already has removed will stay forever.
Some people want to always run "git fetch --prune".

To accommodate users who want to either prune always or when fetching from a particular remote, add two new configuration variables "fetch.prune" and "remote.<name>.prune":

  • "fetch.prune" allows to enable prune for all fetch operations.
  • "remote.<name>.prune" allows to change the behaviour per remote.

The latter will naturally override the former, and the --[no-]prune option from the command line will override the configured default.

Since --prune is a potentially destructive operation (Git doesn't keep reflogs for deleted references yet), we don't want to prune without users consent, so this configuration will not be on by default.

JavaScript: clone a function

This answer is for people who see cloning a function as the answer to their desired usage, but who many not actually need to clone a function, because what they really want is simply to be able to attach different properties to the same function, but only declare that function one time.

Do this by creating a function-creating function:

function createFunction(param1, param2) {
   function doSomething() {
      console.log('in the function!');
   // Assign properties to `doSomething` if desired, perhaps based
   // on the arguments passed into `param1` and `param2`. Or,
   // even return a different function from among a group of them.
   return doSomething;

let a = createFunction();
a.something = 1;
let b = createFunction();
b.something = 2; // does not overwrite a.something

This is not exactly the same as you have outlined, however, it depends on how you want to use the function you're wishing to clone. This also uses more memory because it actually creates multiple copies of the function, once per invocation. However, this technique may solve some people's use case without the need for a complicated clone function.

select and echo a single field from mysql db using PHP

$eventid = $_GET['id'];
$field = $_GET['field'];
$result = mysql_query("SELECT $field FROM `events` WHERE `id` = '$eventid' ");
$row = mysql_fetch_array($result);
echo $row[$field];

but beware of sql injection cause you are using $_GET directly in a query. The danger of injection is particularly bad because there's no database function to escape identifiers. Instead, you need to pass the field through a whitelist or (better still) use a different name externally than the column name and map the external names to column names. Invalid external names would result in an error.

PostgreSQL: how to convert from Unix epoch to date?

select to_timestamp(cast(epoch_ms/1000 as bigint))::date

worked for me

How to install Android SDK on Ubuntu?

sudo add-apt-repository -y ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java7-installer oracle-java7-set-default
cd android-studio/bin

How to force a UIViewController to Portrait orientation in iOS 6

I disagree from @aprato answer, because the UIViewController rotation methods are declared in categories themselves, thus resulting in undefined behavior if you override then in another category. Its safer to override them in a UINavigationController (or UITabBarController) subclass

Also, this does not cover the scenario where you push / present / pop from a Landscape view into a portrait only VC or vice-versa. To solve this tough issue (never addressed by Apple), you should:

In iOS <= 4 and iOS >= 6:

UIViewController *vc = [[UIViewController alloc]init];
[self presentModalViewController:vc animated:NO];
[self dismissModalViewControllerAnimated:NO];
[vc release];

In iOS 5:

UIWindow *window = [[UIApplication sharedApplication] keyWindow];
UIView *view = [window.subviews objectAtIndex:0];
[view removeFromSuperview];
[window addSubview:view];

These will REALLY force UIKit to re-evaluate all your shouldAutorotate , supportedInterfaceOrientations, etc.

C# Inserting Data from a form into an access Database

This answer will help in case, If you are working with Data Bases then mostly take the help of try-catch block statement, which will help and guide you with your code. Here i am showing you that how to insert some values in Data Base with a Button Click Event.

 private void button2_Click(object sender, EventArgs e)
        System.Data.OleDb.OleDbConnection conn = new System.Data.OleDb.OleDbConnection();
        conn.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;" +
    @"Data source= C:\Users\pir fahim shah\Documents\TravelAgency.accdb";

           String ticketno=textBox1.Text.ToString();                 
           String Purchaseprice=textBox2.Text.ToString();
           String sellprice=textBox3.Text.ToString();
           String my_querry = "INSERT INTO Table1(TicketNo,Sellprice,Purchaseprice)VALUES('"+ticketno+"','"+sellprice+"','"+Purchaseprice+"')";

            OleDbCommand cmd = new OleDbCommand(my_querry, conn);

            MessageBox.Show("Data saved successfuly...!");
         catch (Exception ex)
             MessageBox.Show("Failed due to"+ex.Message);

Print specific part of webpage

I made this jQuery extension to print the HTML of the element selected: $('#div2').print();

    print: function() {
        var frameName = 'printIframe';
        var doc = window.frames[frameName];
        if (!doc) {
            $('<iframe>').hide().attr('name', frameName).appendTo(document.body);
            doc = window.frames[frameName];
        doc.document.body.innerHTML = this.html();
        return this;

See it in action here.

Get generic type of class at runtime

I did the same as @Moesio Above but in Kotlin it could be done this way:

class A<T : SomeClass>() {

    var someClassType : T

    this.someClassType = (javaClass.genericSuperclass as ParameterizedType).actualTypeArguments[0] as Class<T>


Unable to create Genymotion Virtual Device

I solved the problem.It was my mistake.
It works fine by running genymotion with administrative privileges.

How to "flatten" a multi-dimensional array to simple one in PHP?

A non-recursive solution (but order-destroying):

function flatten($ar) {
    $toflat = array($ar);
    $res = array();

    while (($r = array_shift($toflat)) !== NULL) {
        foreach ($r as $v) {
            if (is_array($v)) {
                $toflat[] = $v;
            } else {
                $res[] = $v;

    return $res;

Format SQL in SQL Server Management Studio

There is a special trick I discovered by accident.

  1. Select the query you wish to format.
  2. Ctrl+Shift+Q (This will open your query in the query designer)
  3. Then just go OK Voila! Query designer will format your query for you. Caveat is that you can only do this for statements and not procedural code, but its better than nothing.

Long Press in JavaScript?

Based on Maycow Moura's answer, I wrote this. It also ensures that the user didn't do a right click, which would trigger a long press and works on mobile devices. DEMO

var node = document.getElementsByTagName("p")[0];
var longpress = false;
var presstimer = null;
var longtarget = null;

var cancel = function(e) {
    if (presstimer !== null) {
        presstimer = null;


var click = function(e) {
    if (presstimer !== null) {
        presstimer = null;


    if (longpress) {
        return false;


var start = function(e) {

    if (e.type === "click" && e.button !== 0) {

    longpress = false;


    if (presstimer === null) {
        presstimer = setTimeout(function() {
            alert("long click");
            longpress = true;
        }, 1000);

    return false;

node.addEventListener("mousedown", start);
node.addEventListener("touchstart", start);
node.addEventListener("click", click);
node.addEventListener("mouseout", cancel);
node.addEventListener("touchend", cancel);
node.addEventListener("touchleave", cancel);
node.addEventListener("touchcancel", cancel);

You should also include some indicator using CSS animations:

p {
    background: red;
    padding: 100px;

.longpress {
    -webkit-animation: 1s longpress;
            animation: 1s longpress;

@-webkit-keyframes longpress {
    0%, 20% { background: red; }
    100% { background: yellow; }

@keyframes longpress {
    0%, 20% { background: red; }
    100% { background: yellow; }

How does "make" app know default target to build if no target is specified?

To save others a few seconds, and to save them from having to read the manual, here's the short answer. Add this to the top of your make file:

.DEFAULT_GOAL := mytarget

mytarget will now be the target that is run if "make" is executed and no target is specified.

If you have an older version of make (<= 3.80), this won't work. If this is the case, then you can do what anon mentions, simply add this to the top of your make file:

.PHONY: default
default: mytarget ;


Iterate a list with indexes in Python

Here it is a solution using map function:

>>> a = [3, 7, 19]
>>> map(lambda x: (x, a[x]), range(len(a)))
[(0, 3), (1, 7), (2, 19)]

And a solution using list comprehensions:

>>> a = [3,7,19]
>>> [(x, a[x]) for x in range(len(a))]
[(0, 3), (1, 7), (2, 19)]

Check if a string contains another string

There is also the InStrRev function which does the same type of thing, but starts searching from the end of the text to the beginning.

Per @rene's answer...

Dim pos As Integer
pos = InStrRev("find the comma, in the string", ",")

...would still return 15 to pos, but if the string has more than one of the search string, like the word "the", then:

Dim pos As Integer
pos = InStrRev("find the comma, in the string", "the")

...would return 20 to pos, instead of 6.

How do you reverse a string in place in JavaScript?

Keep it DRY and simple silly!!

function reverse(s){
let str = s;
var reverse = '';
for (var i=str.length;i>0;i--){

    var newstr = str.substring(0,i)
    reverse += newstr.substr(-1,1)
return reverse;

CURRENT_TIMESTAMP in milliseconds

For MySQL (5.6+) you can do this:


Which will return (e.g.):

1420998416685 --milliseconds

MySQL - Using COUNT(*) in the WHERE clause


FROM `gd`
group by gid
having count(*) > 10
ORDER BY max(lastupdated) DESC

How can JavaScript save to a local file?

It all depends on what you are trying to achieve with "saving locally". Do you want to allow the user to download the file? then <a download> is the way to go. Do you want to save it locally, so you can restore your application state? Then you might want to look into the various options of WebStorage. Specifically localStorage or IndexedDB. The FilesystemAPI allows you to create local virtual file systems you can store arbitrary data in.

NSOperation vs Grand Central Dispatch

Well, NSOperations are simply an API built on top of Grand Central Dispatch. So when you’re using NSOperations, you’re really still using Grand Central Dispatch. It’s just that NSOperations give you some fancy features that you might like. You can make some operations dependent on other operations, reorder queues after you sumbit items, and other things like that. In fact, ImageGrabber is already using NSOperations and operation queues! ASIHTTPRequest uses them under the hood, and you can configure the operation queue it uses for different behavior if you’d like. So which should you use? Whichever makes sense for your app. For this app it’s pretty simple so we just used Grand Central Dispatch directly, no need for the fancy features of NSOperation. But if you need them for your app, feel free to use it!

Line Break in XML?

In XML a line break is a normal character. You can do this:

  <text>some text
three lines</text>

and the contents of <text> will be

some text
three lines

If this does not work for you, you are doing something wrong. Special "workarounds" like encoding the line break are unnecessary. Stuff like \n won't work, on the other hand, because XML has no escape sequences*.

* Note that &#xA; is the character entity that represents a line break in serialized XML. "XML has no escape sequences" means the situation when you interact with a DOM document, setting node values through the DOM API.

This is where neither &#xA; nor things like \n will work, but an actual newline character will. How this character ends up in the serialized document (i.e. "file") is up to the API and should not concern you.

Since you seem to wonder where your line breaks go in HTML: Take a look into your source code, there they are. HTML ignores line breaks in source code. Use <br> tags to force line breaks on screen.

Here is a JavaScript function that inserts <br> into a multi-line string:

function nl2br(s) { return s.split(/\r?\n/).join("<br>"); }

Alternatively you can force line breaks at new line characters with CSS:

div.lines {
    white-space: pre-line;

Converting Java file:// URL to File(...) path, platform independent, including UNC paths

Java (at least 5 and 6, java 7 Paths solved most) has a problem with UNC and URI. Eclipse team wrapped it up here :

From javadocs, the UNC prefix is "////", and handles file:////host/path (four slashes).

More details on why this happens and possible problems it causes in other URI and URL methods can be found in the list of bugs at the end of the link given above.

Using these informations, Eclipse team developed org.eclipse.core.runtime.URIUtil class, which source code can probably help out when dealing with UNC paths.

Subset data.frame by date

Well, it's clearly not a number since it has dashes in it. The error message and the two comments tell you that it is a factor but the commentators are apparently waiting and letting the message sink in. Dirk is suggesting that you do this:

 EPL2011_12$Date2 <- as.Date( as.character(EPL2011_12$Date), "%d-%m-%y")

After that you can do this:

 EPL2011_12FirstHalf <- subset(EPL2011_12, Date2 > as.Date("2012-01-13") )

R date functions assume the format is either "YYYY-MM-DD" or "YYYY/MM/DD". You do need to compare like classes: date to date, or character to character.

Restarting cron after changing crontab file?

Depending on distribution, using "cron reload" might do nothing. To paste a snippet out of init.d/cron (debian squeeze):

reload|force-reload) log_daemon_msg "Reloading configuration files for periodic command scheduler" "cron"
    # cron reloads automatically
    log_end_msg 0

Some developer/maintainer relied on it reloading, but doesn't, and in this case there's not a way to force reload. I'm generating my crontab files as part of a deploy, and unless somehow the length of the file changes, the changes are not reloaded.

How to get the first non-null value in Java?

Following on from LES2's answer, you can eliminate some repetition in the efficient version, by calling the overloaded function:

public static <T> T coalesce(T a, T b) {
    return a != null ? a : b;
public static <T> T coalesce(T a, T b, T c) {
    return a != null ? a : coalesce(b,c);
public static <T> T coalesce(T a, T b, T c, T d) {
    return a != null ? a : coalesce(b,c,d);
public static <T> T coalesce(T a, T b, T c, T d, T e) {
    return a != null ? a : coalesce(b,c,d,e);

How can I find the first occurrence of a sub-string in a python string?

verse = "If you can keep your head when all about you\n Are losing theirs and blaming it on you,\nIf you can trust yourself when all men doubt you,\n But make allowance for their doubting too;\nIf you can wait and not be tired by waiting,\n Or being lied about, don’t deal in lies,\nOr being hated, don’t give way to hating,\n And yet don’t look too good, nor talk too wise:"

enter code here

#1. What is the length of the string variable verse?
verse_length = len(verse)
print("The length of verse is: {}".format(verse_length))
#2. What is the index of the first occurrence of the word 'and' in verse?
index = verse.find("and")
print("The index of the word 'and' in verse is {}".format(index))

How does String substring work in Swift

Heres a more generic implementation:

This technique still uses index to keep with Swift's standards, and imply a full Character.

extension String
    func subString <R> (_ range: R) -> String? where R : RangeExpression, String.Index == R.Bound
        return String(self[range])

    func index(at: Int) -> Index
        return self.index(self.startIndex, offsetBy: at)

To sub string from the 3rd character:

let item = "Fred looks funny"
item.subString(item.index(at: 2)...) // "ed looks funny"

I've used camel subString to indicate it returns a String and not a Substring.

how to set mongod --dbpath

sudo mongod --dbpath ~/data

This made it work for me.

"detached entity passed to persist error" with JPA/EJB code



because it is auto generate on the DB, and continue with persist command.

how to add or embed CKEditor in php page

<?php require("ckeditor/ckeditor.php"); ?>

 <script type="text/javascript" src="ckeditor/ckeditor.js"></script>
 <script type="text/javascript" src="somedirectory/ckeditor/ckeditor.js"></script>

<textarea class="ckeditor" name="editor1"></textarea>

How can I disable the UITableView selection?

To disable the highlighting of the UItableviewcell

cell.selectionStyle = UITableViewCellSelectionStyleNone;

And should not allow the user to interact with the cell.

cell.userInteractionEnabled = NO;

Typescript: Type X is missing the following properties from type Y length, pop, push, concat, and 26 more. [2740]

I got the same error message on GraphQL mutation input object then I found the problem, Actually in my case mutation expecting an object array as input but I'm trying to insert a single object as input. For example:

First try

const mutationName = await apolloClient.mutate<insert_mutation, insert_mutationVariables>({
      mutation: MUTATION,
      variables: {
        objects: {id: 1, name: "John Doe"},

Corrected mutation call as an array

const mutationName = await apolloClient.mutate<insert_mutation, insert_mutationVariables>({
      mutation: MUTATION,
      variables: {
        objects: [{id: 1, name: "John Doe"}],

Sometimes simple mistakes like this can cause the problems. Hope this'll help someone.

Add quotation at the start and end of each line in Notepad++

  1. Put your cursor at the begining of line 1.
  2. click Edit>ColumnEditor. Put " in the text and hit enter.
  3. Repeat 2 but put the cursor at the end of line1 and put ", and hit enter.

isolating a sub-string in a string before a symbol in SQL Server 2008

This can achieve using two SQL functions- SUBSTRING and CHARINDEX

You can read strings to a variable as shown in the above answers, or can add it to a SELECT statement as below:

SELECT SUBSTRING('Net Operating Loss - 2007' ,0, CHARINDEX('-','Net Operating Loss - 2007'))

@HostBinding and @HostListener: what do they do and what are they for?

Here is a basic hover example.

Component's template property:


<!-- attention, we have the c_highlight class -->
<!-- c_highlight is the selector property value of the directive -->

<p class="c_highlight">
    Some text.

And our directive

import {Component,HostListener,Directive,HostBinding} from '@angular/core';

    // this directive will work only if the DOM el has the c_highlight class
    selector: '.c_highlight'
export class HostDirective {

  // we could pass lots of thing to the HostBinding function. 
  // like class.valid or attr.required etc.

  @HostBinding('style.backgroundColor') c_colorrr = "red"; 

  @HostListener('mouseenter') c_onEnterrr() {
   this.c_colorrr= "blue" ;

  @HostListener('mouseleave') c_onLeaveee() {
   this.c_colorrr = "yellow" ;

C# windows application Event: CLR20r3 on application start

To solve CLR20r3 problem set - Local User Policy \ Computer Configuration \ Windows Settings \ Security Settings \ Local Policies \ Security Options - System cryptography: Use FIPS 140 compliant cryptographic algorithms, including encryption, hashing and signing - Disable

Check if application is installed - Android

Those who are looking for Kotlin solution can use this method,

Here I have shared full code, and also handled enabled status. Check If Application is Installed in Android Kotlin

fun isAppInstalled(packageName: String, context: Context): Boolean {
        return try {
            val packageManager = context.packageManager
            packageManager.getPackageInfo(packageName, 0)
        } catch (e: PackageManager.NameNotFoundException) {

How do I use a char as the case in a switch-case?

Using a char when the variable is a string won't work. Using

switch (hello.charAt(0)) 

you will extract the first character of the hello variable instead of trying to use the variable as it is, in string form. You also need to get rid of your space inside

case 'a '

Best way to handle list.index(might-not-exist) in python?

I have the same issue with the ".index()" method on lists. I have no issue with the fact that it throws an exception but I strongly disagree with the fact that it's a non-descriptive ValueError. I could understand if it would've been an IndexError, though.

I can see why returning "-1" would be an issue too because it's a valid index in Python. But realistically, I never expect a ".index()" method to return a negative number.

Here goes a one liner (ok, it's a rather long line ...), goes through the list exactly once and returns "None" if the item isn't found. It would be trivial to rewrite it to return -1, should you so desire.

indexOf = lambda list, thing: \
            reduce(lambda acc, (idx, elem): \
                   idx if (acc is None) and elem == thing else acc, list, None)

How to use:

>>> indexOf([1,2,3], 4)
>>> indexOf([1,2,3], 1)

How can I "disable" zoom on a mobile web page?

please try adding this meta-tag and style

<meta content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no" name="viewport"/>

        touch-action: manipulation;

define a List like List<int,string>?

Since your example uses a generic List, I assume you don't need an index or unique constraint on your data. A List may contain duplicate values. If you want to insure a unique key, consider using a Dictionary<TKey, TValue>().

var list = new List<Tuple<int,string>>();

list.Add(Tuple.Create(1, "Andy"));
list.Add(Tuple.Create(1, "John"));
list.Add(Tuple.Create(3, "Sally"));

foreach (var item in list)

Writing a dict to txt file and reading it back?

You can iterate through the key-value pair and write it into file

pair = {'name': name,'location': location}
with open('F:\\twitter.json', 'a') as f:
     f.writelines('{}:{}'.format(k,v) for k, v in pair.items())

how to make a specific text on TextView BOLD

Based on @mladj0ni's answer, I got the code below to work. The problem was that if you use String.format, it strips out the html markup, so you have to escape the bracket symbols in strings.xml:


<string name="welcome_messages">Hello, %1$s! You have &lt;b>%2$d new messages&lt;/b>.</string>

String unspanned = String.format(Locale.US, "%s%s", getResources().getString(R.string. welcome_messages), 99);

Spanned spanned;
if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.N) {
    spanned = Html.fromHtml(unspanned, Html.FROM_HTML_MODE_LEGACY);
} else {
    spanned = Html.fromHtml(unspanned);


It's simpler than SpannableStringBuilder. As for performance, if you're displaying just one string, then the user won't notice the extra millisecond to parse it.

See the documentation here.

how to set radio button checked in edit mode in MVC razor view

Don't do this at the view level. Just set the default value to the property in your view model's constructor. Clean and simple. In your post-backs, your selected value will automatically populate the correct selection.

For example

public class MyViewModel
        public MyViewModel()
            Gender = "Male";

 <td><label>@Html.RadioButtonFor(i => i.Gender, "Male")Male</label></td>_x000D_
 <td><label>@Html.RadioButtonFor(i => i.Gender, "Female")Female</label></td>_x000D_

Gets last digit of a number

public static void main(String[] args) {


public static int lastDigit(int number)
    //your code goes here. 
    int last = number % 10;

    return last;



executing shell command in background from script

Leave off the quotes

$cmd &
$othercmd &


nicholas@nick-win7 /tmp
$ cat test

cmd="ls -la"

$cmd &

nicholas@nick-win7 /tmp
$ ./test

nicholas@nick-win7 /tmp
$ total 6
drwxrwxrwt+ 1 nicholas root    0 2010-09-10 20:44 .
drwxr-xr-x+ 1 nicholas root 4096 2010-09-10 14:40 ..
-rwxrwxrwx  1 nicholas None   35 2010-09-10 20:44 test
-rwxr-xr-x  1 nicholas None   41 2010-09-10 20:43 test~

How should I make my VBA code compatible with 64-bit Windows?

I've already encountered this problem on people using my in-house tools on new 64 bit machines with Office 2010.

all I had to do was change lines of code like this:

Private Declare Function ShellExecute Lib "shell32.dll" Alias "ShellExecuteA" _
    (ByVal hwnd As Long, ByVal lpOperation As String, ByVal lpFile As String, ByVal lpParameters As String, ByVal lpDirectory As String, ByVal nShowCmd As Long) As Long

To This:

#If VBA7 Then
    Private Declare PtrSafe Function ShellExecute Lib "shell32.dll" Alias "ShellExecuteA" _
        (ByVal hwnd As Long, ByVal lpOperation As String, ByVal lpFile As String, ByVal lpParameters As String, ByVal lpDirectory As String, ByVal nShowCmd As Long) As Long
    Private Declare Function ShellExecute Lib "shell32.dll" Alias "ShellExecuteA" _
        (ByVal hwnd As Long, ByVal lpOperation As String, ByVal lpFile As String, ByVal lpParameters As String, ByVal lpDirectory As String, ByVal nShowCmd As Long) As Long
#End If

You will, of course want to make sure that the library you're using is available on both machines, but so far nothing I've used has been a problem.

Note that in the old VB6, PtrSafe isn't even a valid command, so it'll appear in red as though you have a compile error, but it won't actually ever give an error because the compiler will skip the first part of the if block.

code Appearance

Applications using the above code compile and run perfectly on Office 2003, 2007, and 2010 32 and 64 bit.

Validate that text field is numeric usiung jQuery

I'm not certain when this was implemented, but currently you can use

if($('#Field').val() != "")
    if($.isNumeric($('#Field').val()) {
        errors+= "Field must be numeric.<br/>";
        success = false;

Android. WebView and loadData

As I understand it, loadData() simply generates a data: URL with the data provide it.

Read the javadocs for loadData():

If the value of the encoding parameter is 'base64', then the data must be encoded as base64. Otherwise, the data must use ASCII encoding for octets inside the range of safe URL characters and use the standard %xx hex encoding of URLs for octets outside that range. For example, '#', '%', '\', '?' should be replaced by %23, %25, %27, %3f respectively.

The 'data' scheme URL formed by this method uses the default US-ASCII charset. If you need need to set a different charset, you should form a 'data' scheme URL which explicitly specifies a charset parameter in the mediatype portion of the URL and call loadUrl(String) instead. Note that the charset obtained from the mediatype portion of a data URL always overrides that specified in the HTML or XML document itself.

Therefore, you should either use US-ASCII and escape any special characters yourself, or just encode everything using Base64. The following should work, assuming you use UTF-8 (I haven't tested this with latin1):

String data = ...;  // the html data
String base64 = android.util.Base64.encodeToString(data.getBytes("UTF-8"), android.util.Base64.DEFAULT);
webView.loadData(base64, "text/html; charset=utf-8", "base64");

Python sum() function with list parameter

Have you used the variable sum anywhere else? That would explain it.

>>> sum = 1
>>> numbers = [1, 2, 3]
>>> numsum = (sum(numbers))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'int' object is not callable

The name sum doesn't point to the function anymore now, it points to an integer.

Solution: Don't call your variable sum, call it total or something similar.

Setting a max height on a table

In Tables, For minimum table cells height or rows height use css height: in place of min-height:


For Limiting max-height of all cells or rows in table with Javascript:

This script is good for horizontal overflow tables.

This script increase the table width 300px each time (maximum 4000px) until rows shrinks to max-height(160px) , and you can also edit numbers as your need.

var i = 0, row, table = document.getElementsByTagName('table')[0], j = table.offsetWidth;
while (row = table.rows[i++]) {
    while (row.offsetHeight > 160 && j < 4000) {
        j += 300; = j + 'px';

Source: HTML Table Solution Max Height Limit For Rows Or Cells By Increasing Table Width, Javascript

What is the fastest factorial function in JavaScript?

Since a factorial is simply degenerative multiplication from the number given down to 1, it would indeed be easier to just loop through the multiplication:

Math.factorial = function(n) {

  if (n === 0||n === 1) {

    return 1;

  } else {

    for(var i = n; i > 0; --i) { //always make sure to decrement the value BEFORE it's tacked onto the original as a product
      n *= i;

    return n;



Use superscripts in R axis labels

It works the same way for axes: parse(text='70^o*N') will raise the o as a superscript (the *N is to make sure the N doesn't get raised too).

labelsX=parse(text=paste(abs(seq(-100, -50, 10)), "^o ", "*W", sep=""))
labelsY=parse(text=paste(seq(50,100,10), "^o ", "*N", sep=""))
plot(-100:-50, 50:100, type="n", xlab="", ylab="", axes=FALSE)
axis(1, seq(-100, -50, 10), labels=labelsX)
axis(2, seq(50, 100, 10), labels=labelsY)

How can I calculate the number of years between two dates?

Bro, moment.js is awesome for this: The diff method is what you want:

The below function return array of years from the year to the current year.

const getYears = (from = 2017) => {_x000D_
  const diff = moment(new Date()).diff(new Date(`01/01/${from}`), 'years') ;_x000D_
  return [...Array(diff >= 0 ? diff + 1 : 0).keys()].map((num) => {_x000D_
    return from + num;_x000D_
<script src=""></script>

Seeding the random number generator in Javascript

A simple approach for a fixed seed:

function fixedrandom(p){
    const seed = 43758.5453123;
    return (Math.abs(Math.sin(p)) * seed)%1;

Convert string to Boolean in javascript

Actually you don't get the meaning of Boolean method.It always return true if the variable is not null or empty.

var variable = some value; Boolean(variable);

If my variable have some value then it will return true else return false You can't use Boolean as you think.

How to import spring-config.xml of one project into spring-config.xml of another project?

A small variation of Sean's answer:

<import resource="classpath*:spring-config.xml" />

With the asterisk in order to spring search files 'spring-config.xml' anywhere in the classpath.

Another reference: Divide Spring configuration across multiple projects

Spring classpath prefix difference

How do you set the title color for the new Toolbar?

This was annoying me a while and I didn't like any of the answers given, so I had a look at the source to see how it works.

FractalWrench is on the right path, but it can be used below API 23 and doesn't have to be set on the toolbar it's self.

As others have said you can set a style on the toolbar with


and in that style you can set the title text colour with

<item name="titleTextColor">#00f</item>

for pre API 23 or for 23+

<item name="android:titleTextColor">your colour</item>

Full xml


<style name="ActionBar" parent="@style/ThemeOverlay.AppCompat.ActionBar">
    <item name="android:titleTextStyle">@style/ActionBarTextStyle</item>
    <item name="titleTextColor">your colour</item>
    <item name="android:background">#ff9900</item>

Heres all the attributes that can be set for a toolbar

<declare-styleable name="Toolbar">
    <attr name="titleTextAppearance" format="reference" />
    <attr name="subtitleTextAppearance" format="reference" />
    <attr name="title" />
    <attr name="subtitle" />
    <attr name="gravity" />
    <attr name="titleMargins" format="dimension" />
    <attr name="titleMarginStart" format="dimension" />
    <attr name="titleMarginEnd" format="dimension" />
    <attr name="titleMarginTop" format="dimension" />
    <attr name="titleMarginBottom" format="dimension" />
    <attr name="contentInsetStart" />
    <attr name="contentInsetEnd" />
    <attr name="contentInsetLeft" />
    <attr name="contentInsetRight" />
    <attr name="maxButtonHeight" format="dimension" />
    <attr name="navigationButtonStyle" format="reference" />
    <attr name="buttonGravity">
        <!-- Push object to the top of its container, not changing its size. -->
        <flag name="top" value="0x30" />
        <!-- Push object to the bottom of its container, not changing its size. -->
        <flag name="bottom" value="0x50" />
    <!-- Icon drawable to use for the collapse button. -->
    <attr name="collapseIcon" format="reference" />
    <!-- Text to set as the content description for the collapse button. -->
    <attr name="collapseContentDescription" format="string" />
    <!-- Reference to a theme that should be used to inflate popups
         shown by widgets in the toolbar. -->
    <attr name="popupTheme" format="reference" />
    <!-- Icon drawable to use for the navigation button located at
         the start of the toolbar. -->
    <attr name="navigationIcon" format="reference" />
    <!-- Text to set as the content description for the navigation button
         located at the start of the toolbar. -->
    <attr name="navigationContentDescription" format="string" />
    <!-- Drawable to set as the logo that appears at the starting side of
         the Toolbar, just after the navigation button. -->
    <attr name="logo" />
    <!-- A content description string to describe the appearance of the
         associated logo image. -->
    <attr name="logoDescription" format="string" />
    <!-- A color to apply to the title string. -->
    <attr name="titleTextColor" format="color" />
    <!-- A color to apply to the subtitle string. -->
    <attr name="subtitleTextColor" format="color" />

Use JavaScript to place cursor at end of text in text input element

I wanted to put cursor at the end of a "div" element where contenteditable = true, and I got a solution with Xeoncross code:

<input type="button" value="Paste HTML" onclick="document.getElementById('test').focus(); pasteHtmlAtCaret('<b>INSERTED</b>'); ">

<div id="test" contenteditable="true">
    Here is some nice text

And this function do magic:

 function pasteHtmlAtCaret(html) {
    var sel, range;
    if (window.getSelection) {
        // IE9 and non-IE
        sel = window.getSelection();
        if (sel.getRangeAt && sel.rangeCount) {
            range = sel.getRangeAt(0);

            // Range.createContextualFragment() would be useful here but is
            // non-standard and not supported in all browsers (IE9, for one)
            var el = document.createElement("div");
            el.innerHTML = html;
            var frag = document.createDocumentFragment(), node, lastNode;
            while ( (node = el.firstChild) ) {
                lastNode = frag.appendChild(node);

            // Preserve the selection
            if (lastNode) {
                range = range.cloneRange();
    } else if (document.selection && document.selection.type != "Control") {
        // IE < 9

Works fine for most browsers, please check it, this code puts text and put focus at the end of the text in div element (not input element)

Thanks, Xeoncross

log4j configuration via JVM argument(s)?

Late to the party as since 2015, Log4J 1.x has reached EOL.

Log4J 2.x onwards the JVM option should be -Dlog4j.configurationFile=<filename>

P.S. <filename> could be a file relative to the class path without the file: as suggested in the other answers.

How does one extract each folder name from a path?

The quick answer is to use the .Split('\\') method.

PHP array() to javascript array()

This may be a easy solution.

var mydate = '<?php implode("##",$youdateArray); ?>';
var ret = mydate.split("##");

How to connect to LocalDB in Visual Studio Server Explorer?

The fastest way in Visual Studio 2017 is to go to Tools -> SQL Server -> New query.. Choose from Local databases and choose the desired Database name at the bottom.

Alternative way

Visual Studio 2017 Server name is:


Add the new connection using menu Tools -> Connect to Database...

Laravel: Get base url

I found an other way to just get the base url to to display the value of environment variable APP_URL


which will display the base url like http://domains_your//yours_website. beware it assumes that you had set the environment variable in .env file (that is present in the root folder).

How to remove leading whitespace from each line in a file

Here you go:

user@host:~$ sed 's/^[\t ]*//g' < file-in.txt


user@host:~$ sed 's/^[\t ]*//g' < file-in.txt > file-out.txt

Add to integers in a list

Yes, it is possible since lists are mutable.

Look at the built-in enumerate() function to get an idea how to iterate over the list and find each entry's index (which you can then use to assign to the specific list item).

How to output numbers with leading zeros in JavaScript?

NOTE: Potentially outdated. ECMAScript 2017 includes String.prototype.padStart.

You'll have to convert the number to a string since numbers don't make sense with leading zeros. Something like this:

function pad(num, size) {
    num = num.toString();
    while (num.length < size) num = "0" + num;
    return num;

Or, if you know you'd never be using more than X number of zeros, this might be better. This assumes you'd never want more than 10 digits.

function pad(num, size) {
    var s = "000000000" + num;
    return s.substr(s.length-size);

If you care about negative numbers you'll have to strip the - and read it.

php get values from json encode

json_decode() will return an object or array if second value it's true:

$json = '{"countryId":"84","productId":"1","status":"0","opId":"134"}';
$json = json_decode($json, true);
echo $json['countryId'];
echo $json['productId'];
echo $json['status'];
echo $json['opId'];

"android.view.WindowManager$BadTokenException: Unable to add window" on

In my case I refactored code and put the creation of the Dialog in a separate class. I only handed over the clicked View because a View contains a context object already. This led to the same error message although all ran on the MainThread.

I then switched to handing over the Activity as well and used its context in the dialog creation -> Everything works now.

    fun showDialogToDeletePhoto(baseActivity: BaseActivity, clickedParent: View, deletePhotoClickedListener: DeletePhotoClickedListener) {
        val dialog = AlertDialog.Builder(baseActivity) // <-- here

I , can't format the code snippet properly, sorry :(

How to enable copy paste from between host machine and virtual machine in vmware, virtual machine is ubuntu

This worked for me. Might want to try editing virtual machine settings:

Click on Edit virtual machine settings

Switch to Always Enabled in Options, Shared Folders

Permission denied (publickey). fatal: The remote end hung up unexpectedly while pushing back to git repository

Googled "Permission denied (publickey). fatal: The remote end hung up unexpectedly", first result an exact SO dupe:

GitHub: Permission denied (publickey). fatal: The remote end hung up unexpectedly which links here in the accepted answer (from the original poster, no less):

How to prevent rm from reporting that a file was not found?

Yes, -f is the most suitable option for this.

Float and double datatype in Java

Floating-point numbers, also known as real numbers, are used when evaluating expressions that require fractional precision. For example, calculations such as square root, or transcendentals such as sine and cosine, result in a value whose precision requires a floating-point type. Java implements the standard (IEEE–754) set of floatingpoint types and operators. There are two kinds of floating-point types, float and double, which represent single- and double-precision numbers, respectively. Their width and ranges are shown here:

   Name     Width in Bits   Range 
    double  64              1 .7e–308 to 1.7e+308
    float   32              3 .4e–038 to 3.4e+038


The type float specifies a single-precision value that uses 32 bits of storage. Single precision is faster on some processors and takes half as much space as double precision, but will become imprecise when the values are either very large or very small. Variables of type float are useful when you need a fractional component, but don't require a large degree of precision.

Here are some example float variable declarations:

float hightemp, lowtemp;


Double precision, as denoted by the double keyword, uses 64 bits to store a value. Double precision is actually faster than single precision on some modern processors that have been optimized for high-speed mathematical calculations. All transcendental math functions, such as sin( ), cos( ), and sqrt( ), return double values. When you need to maintain accuracy over many iterative calculations, or are manipulating large-valued numbers, double is the best choice.

How to pass parameter to click event in Jquery

        alert("The id is "+ );

no need to wrap it in a jquery object

DataTables: Uncaught TypeError: Cannot read property 'defaults' of undefined

I got the same error, I'm using laravel 5.4 with webpack, here package.json before:

  "devDependencies": {
    "jquery": "^1.12.4",
  "dependencies": {
    "": "^2.1.1",

I had to move jquery and npm packages under one of these "dependencies": {} or "devDependencies": {} in package.json and the error disappeared, after:

  "devDependencies": {
    "jquery": "^1.12.4",
    "": "^2.1.1",

I hope that helps!

Calling startActivity() from outside of an Activity context

Intent viewIntent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);    

i hope this will work.

JSONP call showing "Uncaught SyntaxError: Unexpected token : "

Working fiddle:

    url: '',
    dataType: 'JSONP',
    jsonpCallback: 'callback',
    type: 'GET',
    success: function (data) {

I had to manually set the callback to callback, since that's all the remote service seems to support. I also changed the url to specify that I wanted jsonp.

Create component to specific module with Angular-CLI

I am having the similar issues with multiple modules in application. A component can be created to any module so before creating a component we have to specify the name of the particular module.

'ng generate component newCompName --module= specify name of module'

Git undo local branch delete

If you deleted a branch via Source Tree, you could easily find the SHA1 of the deleted branch by going to View -> Show Command History.

It should have the next format:

Deleting branch ...
Deleted branch %NAME% (was %SHA1%)

Then just follow the original answer.

git branch branchName <sha1>

How can I use onItemSelected in Android?

spinner1.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {

               //check if spinner2 has a selected item and show the value in edittext


            public void onNothingSelected(AdapterView<?> parent) {

               // sometimes you need nothing here

spinner2.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {

               //check if spinner1 has a selected item and show the value in edittext


            public void onNothingSelected(AdapterView<?> parent) {

               // sometimes you need nothing here

Cannot open include file: 'unistd.h': No such file or directory

If you're using ZLib in your project, then you need to find :

#if 1

in zconf.h and replace(uncomment) it with :

#if HAVE_UNISTD_H /* ...the rest of the line

If it isn't ZLib I guess you should find some alternative way to do this. GL.

Pandas index column title or name

The solution for multi-indexes is inside jezrael's cyclopedic answer, but it took me a while to find it so I am posting a new answer:

df.index.names gives the names of a multi-index (as a Frozenlist).

Function to calculate R2 (R-squared) in R

You can also use the summary for linear models:

summary(lm(obs ~ mod, data=df))$r.squared 

Convert array to JSON

I made it that way:

if I have:

var jsonArg1 = new Object(); = 'calc this';
    jsonArg1.value = 3.1415;
var jsonArg2 = new Object(); = 'calc this again';
    jsonArg2.value = 2.73;

var pluginArrayArg = new Array();

to convert pluginArrayArg (which is pure javascript array) into JSON array:

var jsonArray = JSON.parse(JSON.stringify(pluginArrayArg))

Thread Safe C# Singleton Pattern

This is called Double checked locking mechanism, first, we will check whether the instance is created or not. If not then only we will synchronize the method and create the instance. It will drastically improve the performance of the application. Performing lock is heavy. So to avoid the lock first we need to check the null value. This is also thread safe and it is the best way to achieve the best performance. Please have a look at the following code.

public sealed class Singleton
    private static readonly object Instancelock = new object();
    private Singleton()
    private static Singleton instance = null;

    public static Singleton GetInstance
            if (instance == null)
                lock (Instancelock)
                    if (instance == null)
                        instance = new Singleton();
            return instance;

How can I use tabs for indentation in IntelliJ IDEA?

File > Settings > Editor > Code Style > Java > Tabs and Indents > Use tab character

Substitute weapon of choice for Java as required.

What is the purpose of the "final" keyword in C++11 for functions?

Supplement to Mario Knezovic 's answer:

class IA
  virtual int getNum() const = 0;

class BaseA : public IA
 inline virtual int getNum() const final {return ...};

class ImplA : public BaseA {...};

IA* pa = ...;
ImplA* impla = static_cast<ImplA*>(pa);

//the following line should cause compiler to use the inlined function BaseA::getNum(), 
//instead of dynamic binding (via vtable or something).
//any class/subclass of BaseA will benefit from it

int n = impla->getNum();

The above code shows the theory, but not actually tested on real compilers. Much appreciated if anyone paste a disassembled output.

How to take a screenshot programmatically on iOS

See this post it looks like you can use UIGetScreenImage() for now.

How do I remove an object from an array with JavaScript?

Use delete-keyword.

delete obj[1];

EDIT: see: Deleting array elements in JavaScript - delete vs splice delete will undefine the offset but not completly remove the entry. Splice would be correct like David said.

Simple line plots using seaborn

It's possible to get this done using seaborn.lineplot() but it involves some additional work of converting numpy arrays to pandas dataframe. Here's a complete example:

# imports
import seaborn as sns
import numpy as np
import pandas as pd

# inputs
In [41]: num = np.array([1, 2, 3, 4, 5])
In [42]: sqr = np.array([1, 4, 9, 16, 25])

# convert to pandas dataframe
In [43]: d = {'num': num, 'sqr': sqr}
In [44]: pdnumsqr = pd.DataFrame(d)

# plot using lineplot
In [45]: sns.set(style='darkgrid')
In [46]: sns.lineplot(x='num', y='sqr', data=pdnumsqr)
Out[46]: <matplotlib.axes._subplots.AxesSubplot at 0x7f583c05d0b8>

And we get the following plot:

square plot

How to define a variable in a Dockerfile?

You can use ARG variable defaultValue and during the run command you can even update this value using --build-arg variable=value. To use these variables in the docker file you can refer them as $variable in run command.

Note: These variables would be available for Linux commands like RUN echo $variable and they wouldn't persist in the image.

Warning: mysqli_query() expects parameter 1 to be mysqli, null given in

As mentioned in comments, this is a scoping issue. Specifically, $con is not in scope within your getPosts function.

You should pass your connection object in as a dependency, eg

function getPosts(mysqli $con) {
    // etc

I would also highly recommend halting execution if your connection fails or if errors occur. Something like this should suffice

mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT); // throw exceptions


Include another HTML file in a HTML file

Shameless plug of a library that I wrote the solve this.

<div data-include="/path/to/include.html"></div>

The above will take the contents of /path/to/include.html and replace the div with it.

ModuleNotFoundError: No module named 'sklearn'


Conda and pip install scikit-learn under ~/anaconda3/envs/$ENV/lib/python3.7/site-packages, however Jupyter notebook looks for the package under ~/anaconda3/lib/python3.7/site-packages.

Therefore, even when the environment is specified to conda, it does not work.

conda install -n $ENV scikit-learn # Does not work


pip 3 install the package under ~/anaconda3/lib/python3.7/site-packages.


After pip3, in a Jupyter notebook.

import sklearn


How to run vbs as administrator from vbs?

This is the universal and best solution for this:

If WScript.Arguments.Count <> 1 Then WScript.Quit 1

Sub RunAsAdmin()
    Set Shell = CreateObject("WScript.Shell")
    Set Env = Shell.Environment("VOLATILE")
    If Shell.Run("%ComSpec% /C ""NET FILE""", 0, True) <> 0 Then
        Env("CurrentDirectory") = Shell.CurrentDirectory
        ArgsList = ""
        For i = 1 To WScript.Arguments.Count
            ArgsList = ArgsList & """ """ & WScript.Arguments(i - 1)
        CreateObject("Shell.Application").ShellExecute WScript.FullName, """" & WScript.ScriptFullName & ArgsList & """", , "runas", 5
        WScript.Sleep 100
    End If
    If Env("CurrentDirectory") <> "" Then Shell.CurrentDirectory = Env("CurrentDirectory")
End Sub

Sub Main()
    'Your code here!
End Sub


1) The parameter injection is not possible.
2) The number of arguments does not change after the elevation to administrator and then you can check them before you elevate yourself.
3) You know for real and immediately if the script runs as an administrator. For example, if you call it from a control panel uninstallation entry, the RunAsAdmin function will not run unnecessarily because in that case you are already an administrator. Same thing if you call it from a script already elevated to administrator.
4) The window is kept at its current size and position, as it should be.
5) The current directory doesn't change after obtained administrative privileges.

Disadvantages: Nobody

Remove duplicated rows using dplyr

Here is a solution using dplyr >= 0.5.

df <- data.frame(
  x = sample(0:1, 10, replace = T),
  y = sample(0:1, 10, replace = T),
  z = 1:10

> df %>% distinct(x, y, .keep_all = TRUE)
    x y z
  1 0 1 1
  2 1 0 2
  3 1 1 4

How do I implement a progress bar in C#?

The idea behind reporting progress with the background worker is through sending a 'percent completed' event. You are yourself responsible for determining somehow 'how much' work has been completed. Unfortunately this is often the most difficult part.

In your case, the bulk of the work is database-related. There is to my knowledge no way to get progress information from the DB directly. What you can try to do however, is split up the work dynamically. E.g., if you need to read a lot of data, a naive way to implement this could be.

  • Determine how many rows are to be retrieved (SELECT COUNT(*) FROM ...)
  • Divide the actual reading in smaller chunks, reporting progress every time one chunk is completed:

    for (int i = 0; i < count; i++)
        bgWorker.ReportProgress((100 * i) / count);
        // ... (read data for step i)

How to align linearlayout to vertical center?

use RelativeLayout inside LinearLayout



Delete certain lines in a txt file via a batch file

If you have sed:

sed -e '/REFERENCE/d' -e '/ERROR/d' [FILENAME]

Where FILENAME is the name of the text file with the good & bad lines

Redirect with CodeIgniter

first, you need to load URL helper like this type or you can upload within autoload.php file:


if (!$user_logged_in)
  redirect('/account/login', 'refresh');

How do you find out the caller function in JavaScript?

You can get the full stacktrace:


Until caller is null.

Note: it cause an infinite loop on recursive functions.

How can I copy a conditional formatting from one document to another?

If you want to copy conditional formatting to another document you can use the "Copy to..." feature for the worksheet (click the tab with the name of the worksheet at the bottom) and copy the worksheet to the other document.

Then you can just copy what you want from that worksheet and right-click select "Paste special" -> "Paste conditional formatting only", as described earlier.

Problems after upgrading to Xcode 10: Build input file cannot be found

This worked for me

  1. try deleting the red colored files
  2. delete the files in derived data
  3. clean the build folder
  4. then try building by using "new build system" from file->workspace settings

Check if an apt-get package is installed and then install it if it's not on Linux

which <command>
if [ $? == 1 ]; then
    <pkg-manager> -y install <command>

how to count the total number of lines in a text file using python

For the people saying to use with open ("filename.txt","r") as f you can do anyname = open("filename.txt","r")

def main():

    file = open("infile.txt",'r')
    count = 0
    for line in file:

    print (count)

main ()

java: Class.isInstance vs Class.isAssignableFrom

For brevity, we can understand these two APIs like below:

  1. X.class.isAssignableFrom(Y.class)

If X and Y are the same class, or X is Y's super class or super interface, return true, otherwise, false.

  1. X.class.isInstance(y)

Say y is an instance of class Y, if X and Y are the same class, or X is Y's super class or super interface, return true, otherwise, false.

Android getting value from selected radiobutton

Thanks a lot to Chris.

This is my solution:

RadioGroup radgroup_opcionesEventos = null;

 private static String[] arrayEventos = {
            "Congestión", "Derrumbe", "Accidente"
    protected void onCreate(Bundle savedInstanceState)
        radgroup_opcionesEventos = (RadioGroup)findViewById(;
        int i=0;//
        for(String evento : arrayEventos) {
            //RadioButton nuevoRadio = crearRadioButton(evento);//a.old.ln
            RadioButton nuevoRadio = crearRadioButton(evento,i);//

        RadioButton primerRadio = (RadioButton) radgroup_opcionesEventos.getChildAt(0);

private RadioButton crearRadioButton(String evento, int n)
        //RadioButton nuevoRadio = new RadioButton(this);//a.old.ln
        RadioButton nuevoRadio = new RadioButton(getApplicationContext());//

        LinearLayout.LayoutParams params = new RadioGroup.LayoutParams(
        return nuevoRadio;

    protected void onResume()
        radgroup_opcionesEventos.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
            public void onCheckedChanged(RadioGroup group, int checkedId) {
                RadioButton radioButton = (RadioButton) group.findViewById(checkedId);
                //int mySelectedIndex = (int) radioButton.getTag();
                String mySelectedIndex = radioButton.getTag().toString();

Finding Key associated with max Value in a Java Map

An answer that returns an Optional since the map may have no max value if it is empty: map.entrySet().stream().max(Map.Entry.comparingByValue()).map(Map.Entry::getKey);

How to implement Android Pull-to-Refresh

If you don't want your program to look like an iPhone program that is force fitted into Android, aim for a more native look and feel and do something similar to Gingerbread:

alt text