Programs & Examples On #Mongodb

MongoDB is a scalable, high-performance, open source, document-oriented NoSQL database. It supports a large number of languages and application development platforms. Questions about server administration can be asked on

What are naming conventions for MongoDB?

Even if no convention is specified about this, manual references are consistently named after the referenced collection in the Mongo documentation, for one-to-one relations. The name always follows the structure <document>_id.

For example, in a dogs collection, a document would have manual references to external documents named like this:

  name: 'fido',
  owner_id: '5358e4249611f4a65e3068ab',
  race_id: '5358ee549611f4a65e3068ac',
  colour: 'yellow'

This follows the Mongo convention of naming _id the identifier for every document.

MongoDB "root" user

While out of the box, MongoDb has no authentication, you can create the equivalent of a root/superuser by using the "any" roles to a specific user to the admin database.

Something like this:

use admin
db.addUser( { user: "<username>",
          pwd: "<password>",
          roles: [ "userAdminAnyDatabase",

] } )

Update for 2.6+

While there is a new root user in 2.6, you may find that it doesn't meet your needs, as it still has a few limitations:

Provides access to the operations and all the resources of the readWriteAnyDatabase, dbAdminAnyDatabase, userAdminAnyDatabase and clusterAdmin roles combined.

root does not include any access to collections that begin with the system. prefix.

Update for 3.0+

Use db.createUser as db.addUser was removed.

Update for 3.0.7+

root no longer has the limitations stated above.

The root has the validate privilege action on system. collections. Previously, root does not include any access to collections that begin with the system. prefix other than system.indexes and system.namespaces.

MongoDB query multiple collections at once

Perform multiple queries or use embedded documents or look at "database references".

Check the current number of connections to MongoDb

I tried to see all connections for mongo database by following command.

netstat -anp --tcp --udp | grep mongo

This command can show every tcp connection for mongodb in more detail.

tcp        0      0               ESTABLISHED 1442/./mongod       
tcp        0      0               ESTABLISHED 1442/./mongod  
tcp        0      0            ESTABLISHED 1442/./mongod       
tcp        0      0            ESTABLISHED 1442/./mongod       
tcp        0      0            ESTABLISHED 1442/./mongod 
tcp        0      0            ESTABLISHED 1442/./mongod       
tcp        0      0            ESTABLISHED 1442/./mongod       
tcp        0      0            ESTABLISHED 1442/./mongod   

How to list all databases in the mongo shell?

To list mongodb database on shell

 show databases     //Print a list of all available databases.
 show dbs   // Print a list of all databases on the server.

Few more basic commands

use <db>    // Switch current database to <db>. The mongo shell variable db is set to the current database.
show collections    //Print a list of all collections for current database.
show users  //Print a list of users for current database.
show roles  //Print a list of all roles, both user-defined and built-in, for the current database.

How to get the Mongo database specified in connection string in C#

The answer below is apparently obsolete now, but works with older drivers. See comments.

If you have the connection string you could also use MongoDatabase directly:

var db =  MongoDatabase.Create(connectionString);
var coll = db.GetCollection("MyCollection");

MongoDB relationships: embed or reference?

MongoDB gives freedom to be schema-less and this feature can result in pain in the long term if not thought or planned well,

There are 2 options either Embed or Reference. I will not go through definitions as the above answers have well defined them.

When embedding you should answer one question is your embedded document going to grow, if yes then how much (remember there is a limit of 16 MB per document) So if you have something like a comment on a post, what is the limit of comment count, if that post goes viral and people start adding comments. In such cases, reference could be a better option (but even reference can grow and reach 16 MB limit).

So how to balance it, the answer is a combination of different patterns, check these links, and create your own mix and match based on your use case.

Unable to connect to mongodb Error: couldn't connect to server at src/mongo/shell/mongo.js:L112

Mongo DB requires space to store it files. So you should create folder structure for Mongo DB before starting the Mongodb server/client.

for e.g. MongoDb/Dbfiles where Mongo DB is installed.

Then in cmd promt exe mongod.exe and mongo.exe for client and done.

How can I rename a field for all documents in MongoDB?

please try db.collectionName.update({}, { $rename : { 'name.additional' : 'name.last' } }, { multi: true } )

and read this :)

$lookup on ObjectId's in an array

use $unwind you will get the first object instead of array of objects


    $match: {
      status: "AVAILABLE",
      vehicleTypeId: {
        $in: Array.from(newSet(d.vehicleTypeIds))
    $lookup: {
      from: "servicelocations",
      localField: "locationId",
      foreignField: "serviceLocationId",
      as: "locations"
    $unwind: "$locations"


    "_id" : ObjectId("59c3983a647101ec58ddcf90"),
    "vehicleId" : "45680",
    "regionId" : 1.0,
    "vehicleTypeId" : "10TONBOX",
    "locationId" : "100",
    "description" : "Isuzu/2003-10 Ton/Box",
    "deviceId" : "",
    "earliestStart" : 36000.0,
    "latestArrival" : 54000.0,
    "status" : "AVAILABLE",
    "accountId" : 1.0,
    "locations" : {
        "_id" : ObjectId("59c3afeab7799c90ebb3291f"),
        "serviceLocationId" : "100",
        "regionId" : 1.0,
        "zoneId" : "DXBZONE1",
        "description" : "Masafi Park Al Quoz",
        "locationPriority" : 1.0,
        "accountTypeId" : 0.0,
        "locationType" : "DEPOT",
        "location" : {
            "makani" : "",
            "lat" : 25.123091,
            "lng" : 55.21082
        "deliveryDays" : "MTWRFSU",
        "timeWindow" : {
            "timeWindowTypeId" : "1"
        "address1" : "",
        "address2" : "",
        "phone" : "",
        "city" : "",
        "county" : "",
        "state" : "",
        "country" : "",
        "zipcode" : "",
        "imageUrl" : "",
        "contact" : {
            "name" : "",
            "email" : ""
        "status" : "",
        "createdBy" : "",
        "updatedBy" : "",
        "updateDate" : "",
        "accountId" : 1.0,
        "serviceTimeTypeId" : "1"

    "_id" : ObjectId("59c3983a647101ec58ddcf91"),
    "vehicleId" : "81765",
    "regionId" : 1.0,
    "vehicleTypeId" : "10TONBOX",
    "locationId" : "100",
    "description" : "Hino/2004-10 Ton/Box",
    "deviceId" : "",
    "earliestStart" : 36000.0,
    "latestArrival" : 54000.0,
    "status" : "AVAILABLE",
    "accountId" : 1.0,
    "locations" : {
        "_id" : ObjectId("59c3afeab7799c90ebb3291f"),
        "serviceLocationId" : "100",
        "regionId" : 1.0,
        "zoneId" : "DXBZONE1",
        "description" : "Masafi Park Al Quoz",
        "locationPriority" : 1.0,
        "accountTypeId" : 0.0,
        "locationType" : "DEPOT",
        "location" : {
            "makani" : "",
            "lat" : 25.123091,
            "lng" : 55.21082
        "deliveryDays" : "MTWRFSU",
        "timeWindow" : {
            "timeWindowTypeId" : "1"
        "address1" : "",
        "address2" : "",
        "phone" : "",
        "city" : "",
        "county" : "",
        "state" : "",
        "country" : "",
        "zipcode" : "",
        "imageUrl" : "",
        "contact" : {
            "name" : "",
            "email" : ""
        "status" : "",
        "createdBy" : "",
        "updatedBy" : "",
        "updateDate" : "",
        "accountId" : 1.0,
        "serviceTimeTypeId" : "1"

Failed to auto-configure a DataSource: 'spring.datasource.url' is not specified

I ran into this problem when I simply mistyped my jdbc url in Hope this helps someone: before:




How to get all count of mongoose model?

The highest voted answers here are perfectly fine I just want to add up the use of await so that the functionality asked for can be archived:

const documentCount = await userModel.count({});
console.log( "Number of users:", documentCount );

It's recommended to use countDocuments() over 'count()' as it will be deprecated going on. So, for now, the perfect code would be:

const documentCount = await userModel.countDocuments({});
console.log( "Number of users:", documentCount );

How to export collection to CSV in MongoDB?

Below command used to export collection to CSV format.

Note: naag is database, employee1_json is a collection.

mongoexport --db naag--collection employee1_json --type csv --out /home/orienit/work/mongodb/employee1_csv_op1

Pretty print in MongoDB shell as default

Got to the question but could not figure out how to print it from externally-loaded mongo. So:

This works is for console: and is prefered in console, but does not work in external mongo-loaded javascript:


This works in external mongo-loaded javscript:


MongoDB - Update objects in a document's array (nested updating)

There is no way to do this in single query. You have to search the document in first query:

If document exists: {user_id : 123456 , "items.item_name" : "my_item_two" } , 
                {$inc : {"items.$.price" : 1} } , 
                false , 

Else {user_id : 123456 } , 
                {$addToSet : {"items" : {'item_name' : "my_item_two" , 'price' : 1 }} } ,
                false , 

No need to add condition {$ne : "my_item_two" }.

Also in multithreaded enviourment you have to be careful that only one thread can execute the second (insert case, if document did not found) at a time, otherwise duplicate embed documents will be inserted.

How can you remove all documents from a collection with Mongoose?

.remove() is deprecated. instead we can use deleteMany

DateTime.deleteMany({}, callback).

What's a clean way to stop mongod on Mac OS X?

It's probably because launchctl is managing your mongod instance. If you want to start and shutdown mongod instance, unload that first:

launchctl unload -w ~/Library/LaunchAgents/org.mongodb.mongod.plist

Then start mongod manually:

mongod -f path/to/mongod.conf --fork

You can find your mongod.conf location from ~/Library/LaunchAgents/org.mongodb.mongod.plist.

After that, db.shutdownServer() would work just fine.

Added Feb 22 2014:

If you have mongodb installed via homebrew, homebrew actually has a handy brew services command. To show current running services:

brew services list

To start mongodb:

brew services start mongodb-community

To stop mongodb if it's already running:

brew services stop mongodb-community


As edufinn pointed out in the comment, brew services is now available as user-defined command and can be installed with following command: brew tap gapple/services.

Best way to store date/time in mongodb

One datestamp is already in the _id object, representing insert time

So if the insert time is what you need, it's already there:

Login to mongodb shell

ubuntu@ip-10-0-1-223:~$ mongo
MongoDB shell version: 2.4.9
connecting to:

Create your database by inserting items

> db.penguins.insert({"penguin": "skipper"})
> db.penguins.insert({"penguin": "kowalski"})

Lets make that database the one we are on now

> use penguins
switched to db penguins

Get the rows back:

> db.penguins.find()
{ "_id" : ObjectId("5498da1bf83a61f58ef6c6d5"), "penguin" : "skipper" }
{ "_id" : ObjectId("5498da28f83a61f58ef6c6d6"), "penguin" : "kowalski" }

Get each row in yyyy-MM-dd HH:mm:ss format:

> db.penguins.find().forEach(function (doc){ d = doc._id.getTimestamp(); print(d.getFullYear()+"-"+(d.getMonth()+1)+"-"+d.getDate() + " " + d.getHours() + ":" + d.getMinutes() + ":" + d.getSeconds()) })
2014-12-23 3:4:41
2014-12-23 3:4:53

If that last one-liner confuses you I have a walkthrough on how that works here:

Mongoose: CastError: Cast to ObjectId failed for value "[object Object]" at path "_id"

For the record: I had this error trying to fill a subdocument in a wrong way:

[CastError: Cast to ObjectId failed for value "[object Object]" at path "_id"]
message: 'Cast to ObjectId failed for value "[object Object]" at path "_id"',
name: 'CastError',
type: 'ObjectId',
path: '_id'
  [ { timestamp: '2014-07-03T00:23:45-04:00',
  date_start: '2014-07-03T00:23:45-04:00',
  date_end: '2014-07-03T00:23:45-04:00',
  operation: 'Deactivation' } ],

look ^ value is an array containing an object: wrong!

Explanation: I was sending data from php to a node.js API in this way:

$history = json_encode(
  'timestamp'  => date('c', time()),
  'date_start' => date('c', time()),
  'date_end'   => date('c', time()),
  'operation'  => 'Deactivation'

As you can see $history is an array containing an array. That's why mongoose try to fill _id (or any other field) with an array instead than a Scheme.ObjectId (or any other data type). The following works:

$history = json_encode(
  'timestamp'  => date('c', time()),
  'date_start' => date('c', time()),
  'date_end'   => date('c', time()),
  'operation'  => 'Deactivation'

Mongoose and multiple database in single node.js project

Mongoose and multiple database in single node.js project

use useDb to solve this issue


//product databse

const myDB = mongoose.connection.useDb('product');

module.exports = myDB.model("Snack", snackSchema);

//user databse

const myDB = mongoose.connection.useDb('user');

module.exports = myDB.model("User", userSchema);

Get the _id of inserted document in Mongo database in NodeJS

I actually did a console.log() for the second parameter in the callback function for insert. There is actually a lot of information returned apart from the inserted object itself. So the code below explains how you can access it's id.

collection.insert(objToInsert, function (err, result){
    else {
        // The above statement will output the id of the 
        // inserted object

"continue" in cursor.forEach()

In my opinion the best approach to achieve this by using the filter method as it's meaningless to return in a forEach block; for an example on your snippet:

// Fetch all objects in SomeElements collection
var elementsCollection = SomeElements.find();
.filter(function(element) {
  return element.shouldBeProcessed;

This will narrow down your elementsCollection and just keep the filtred elements that should be processed.

How to use mongoimport to import csv

use :

mongoimport -d 'database_name' -c 'collection_name' --type csv --headerline --file filepath/file_name.csv

How do I connect to mongodb with node.js (and authenticate)?

Here is new may to authenticate from "admin" and then switch to your desired DB for further operations:

   var MongoClient = require('mongodb').MongoClient;
var Db = require('mongodb').Db, Server = require('mongodb').Server ,
    assert = require('assert');

var user = 'user';
var password = 'password';

MongoClient.connect('mongodb://'+user+':'+password+'@localhost:27017/opsdb',{native_parser:true, authSource:'admin'}, function(err,db){
        console.log("Auth Failed");
    db.collection("cols").find({loc:{ $eq: null } }, function(err, docs) {
        docs.each(function(err, doc) {
          if(doc) {



MongoNetworkError: failed to connect to server [localhost:27017] on first connect [MongoNetworkError: connect ECONNREFUSED]

Many of them don't add this, especially in AWS EC2 Instance, I had the same issue and tried different solutions. Solution: one of my database URL inside the code was missing this parameter 'authSource', adding this worked for me.


Get names of all keys in the collection

Try this:

for (key in doc) print(key);

MongoDB or CouchDB - fit for production?

This question has already accepted answer but now a days one more NoSQL DB is in trend for many of its great features. It is Couchbase; which runs as CouchbaseLite on mobile platform and Couchbase Server on your server side.

Here is some of main features of Couchbase Lite.

Couchbase Lite is a lightweight, document-oriented (NoSQL), syncable database engine suitable for embedding into mobile apps.

Lightweight means:

Embedded—the database engine is a library linked into the app, not a separate server process. Small code size—important for mobile apps, which are often downloaded over cell networks. Quick startup time—important because mobile devices have relatively slow CPUs. Low memory usage—typical mobile data sets are relatively small, but some documents might have large multimedia attachments. Good performance—exact figures depend on your data and application, of course.

Document-oriented means:

Stores records in flexible JSON format instead of requiring predefined schemas or normalization. Documents can have arbitrary-sized binary attachments, such as multimedia content. Application data format can evolve over time without any need for explicit migrations. MapReduce indexing provides fast lookups without needing to use special query languages.

Syncable means:

Any two copies of a database can be brought into sync via an efficient, reliable, proven replication algorithm. Sync can be on-demand or continuous (with a latency of a few seconds). Devices can sync with a subset of a large database on a remote server. The sync engine supports intermittent and unreliable network connections. Conflicts can be detected and resolved, with app logic in full control of merging. Revision trees allow for complex replication topologies, including server-to-server (for multiple data centers) and peer-to-peer, without data loss or false conflicts. Couchbase Lite provides native APIs for seamless iOS (Objective-C) and Android (Java) development. In addition, it includes the Couchbase Lite Plug-in for PhoneGap, which enables you to build iOS and Android apps that you develop by using familiar web-application programming techniques and the PhoneGap mobile development framework.

You can explore more on Couchbase Lite

and Couchbase Server

This is going to the next big thing.

How do you query for "is not null" in Mongo?

Sharing for future readers.

This query worked for us (query executed from MongoDB compass):

  "fieldName": {
    "$nin": [

Uninstall mongoDB from ubuntu

To uninstalling existing MongoDB packages. I think this link will helpful.

How do I perform the SQL Join equivalent in MongoDB?

You can run SQL queries including join on MongoDB with mongo_fdw from Postgres.

Combine two OR-queries with AND in Mongoose

It's probably easiest to create your query object directly as:

      $and: [
          { $or: [{a: 1}, {b: 1}] },
          { $or: [{c: 1}, {d: 1}] }
  }, function (err, results) {

But you can also use the Query#and helper that's available in recent 3.x Mongoose releases:

          { $or: [{a: 1}, {b: 1}] },
          { $or: [{c: 1}, {d: 1}] }
      .exec(function (err, results) {

Mongoose.js: Find user by username LIKE value

Here my code with expressJS:

    .get(function(request, response) {
            var word = request.params.word;       
            Word.find({'sentence' : new RegExp(word, 'i')}, function(err, words){
               if (err) {response.send(err);}

MySQL vs MongoDB 1000 reads

Here is a little research that explored RDBMS vs NoSQL using MySQL vs Mongo, the conclusions were inline with @Sean Reilly's response. In short, the benefit comes from the design, not some raw speed difference. Conclusion on page 35-36:

RDBMS vs NoSQL: Performance and Scaling Comparison

The project tested, analysed and compared the performance and scalability of the two database types. The experiments done included running different numbers and types of queries, some more complex than others, in order to analyse how the databases scaled with increased load. The most important factor in this case was the query type used as MongoDB could handle more complex queries faster due mainly to its simpler schema at the sacrifice of data duplication meaning that a NoSQL database may contain large amounts of data duplicates. Although a schema directly migrated from the RDBMS could be used this would eliminate the advantage of MongoDB’s underlying data representation of subdocuments which allowed the use of less queries towards the database as tables were combined. Despite the performance gain which MongoDB had over MySQL in these complex queries, when the benchmark modelled the MySQL query similarly to the MongoDB complex query by using nested SELECTs MySQL performed best although at higher numbers of connections the two behaved similarly. The last type of query benchmarked which was the complex query containing two JOINS and and a subquery showed the advantage MongoDB has over MySQL due to its use of subdocuments. This advantage comes at the cost of data duplication which causes an increase in the database size. If such queries are typical in an application then it is important to consider NoSQL databases as alternatives while taking in account the cost in storage and memory size resulting from the larger database size.

Mongoose's find method with $or condition does not work properly

I implore everyone to use Mongoose's query builder language and promises instead of callbacks:

User.find().or([{ name: param }, { nickname: param }])
    .then(users => { /*logic here*/ })
    .catch(error => { /*error logic here*/ })

Read more about Mongoose Queries.

how to query child objects in mongodb

If it is exactly null (as opposed to not set):

db.states.find({"": null})

(but as javierfp points out, it also matches documents that have no cities array at all, I'm assuming that they do).

If it's the case that the property is not set:

db.states.find({"": {"$exists": false}})

I've tested the above with a collection created with these two inserts:

db.states.insert({"cities": [{name: "New York"}, {name: null}]})
db.states.insert({"cities": [{name: "Austin"}, {color: "blue"}]})

The first query finds the first state, the second query finds the second. If you want to find them both with one query you can make an $or query:

db.states.find({"$or": [
  {"": null}, 
  {"": {"$exists": false}}

Cannot start MongoDB as a service

Just try to run mongod.exe locally in command line, you can get here exception, that mongod calls and try to solve it. In my case it was small free space on local disc, so I just change location of directories and change Mongocofig file and now it run ok.

Mongoose, Select a specific field with find

The _id field is always present unless you explicitly exclude it. Do so using the - syntax:

exports.someValue = function(req, res, next) {
    //query with mongoose
    var query = dbSchemas.SomeValue.find({}).select('name -_id');

    query.exec(function (err, someValue) {
        if (err) return next(err);

Or explicitly via an object:

exports.someValue = function(req, res, next) {
    //query with mongoose
    var query = dbSchemas.SomeValue.find({}).select({ "name": 1, "_id": 0});

    query.exec(function (err, someValue) {
        if (err) return next(err);

nodejs mongodb object id to string

function encodeToken(token){
    //token must be a string .
    token = typeof token == 'string' ? token : String(token)

User.findOne({name: 'elrrrrrrr'}, function(err, it) {

In mongoose , the objectId is an object (console.log(typeof it._id)).

Dump Mongo Collection into JSON format

If you want to dump all collections, run this command:

mongodump -d {DB_NAME}   -o /tmp 

It will generate all collections data in json and bson extensions into /tmp/{DB_NAME} directory

How to sort a collection by date in MongoDB?


This will sort your collection in descending order based on the date of insertion

Which SchemaType in Mongoose is Best for Timestamp?

The current version of Mongoose (v4.x) has time stamping as a built-in option to a schema:

var mySchema = new mongoose.Schema( {name: String}, {timestamps: true} );

This option adds createdAt and updatedAt properties that are timestamped with a Date, and which does all the work for you. Any time you update the document, it updates the updatedAt property. Schema Timestamps Docs.

How do I search for an object by its ObjectId in the mongo console?

If you're using Node.js:

> var ObjectId = require('mongodb').ObjectId; 
> var id = req.params.gonderi_id;       
> var o_id = new ObjectId(id);
> db.test.find({_id:o_id})

Edit: corrected to new ObjectId(id), not new ObjectID(id)

Location of the mongodb database on mac

I had the same problem, with version 3.4.2

to run it (if you installed it with homebrew) run the process like this:

$ mongod --dbpath /usr/local/var/mongodb

Random record from MongoDB

The following aggregation operation randomly selects 3 documents from the collection:

db.users.aggregate( [ { $sample: { size: 3 } } ] )

MongoDB vs Firebase

Firebase is a suite of features .

  • Realtime Database
  • Hosting
  • Authentication
  • Storage
  • Cloud Messaging
  • Remote Config
  • Test Lab
  • Crash Reporting
  • Notifications
  • App Indexing
  • Dynamic Links
  • Invites
  • AdWords
  • AdMob

I believe you are trying to compare Firebase Realtime Database with Mongo DB . Firebase Realtime Database stores data as JSON format and syncs to all updates of the data to all clients listening to the data . It abstracts you from all complexity that is needed to setup and scale any database . I will not recommend firebase where you have lot of complex scenarios where aggregation of data is needed .(Queries that need SUM/AVERAGE kind of stuff ) . Though this is recently achievable using Firebase functions . Modeling data in Firebase is tricky . But it is the best way to get you started instantaneously . MongoDB is a database. This give you lot of powerful features. But MongoDB when installed in any platform you need to manage it by yourself .

When i try to choose between Firebase or MongoDB(or any DB ) . I try to answer the following .

  1. Are there many aggregation queries that gets executed .(Like in case of reporting tool or BI tool ) . If Yes dont go for Firebase
  2. Do i need to perform lot of transaction . (If yes then i would not like to go with firebase) (Tranactions are somewhat easy though after introduction of functions but that is also a overhead if lot of transactions needs to be maintained)
  3. What timeline do i have to get things up and running .(Firebase is very easy to setup and integrate ).
  4. Do i have expertise to scale up the DB and trouble shoot DB related stuffs . (Firebase is more like SAAS so no need to worry about scaleability)

How to secure MongoDB with username and password

First run mongoDB on terminal using


now run mongo shell use following commands

    use admin
    user: "myUserAdmin",
    pwd: "abc123",
    roles: [ { role: "userAdminAnyDatabase", db: "admin" } ]

Re-start the MongoDB instance with access control.

mongod --auth

Now authenticate yourself from the command line using

mongo --port 27017 -u "myUserAdmin" -p "abc123" --authenticationDatabase "admin"

I read it from

How to Import .bson file format on mongodb

Run the following from command line and you should be in the Mongo bin directory.

mongorestore -d db_name -c collection_name path/file.bson

Mongodb: Failed to connect to, reason: errno:10061

The problem is that I missed out 'db' folder for the dbpath in the command:

C:\mongodb\bin> mongod --directoryperdb --dbpath C:\mongodb\data\db --logpath C:\mongodb\log\mongodb.log --logappend -rest --install

Comparing mongoose _id and strings

The accepted answers really limit what you can do with your code. For example, you would not be able to search an array of Object Ids by using the equals method. Instead, it would make more sense to always cast to string and compare the keys.

Here's an example answer in case if you need to use indexOf() to check within an array of references for a specific id. assume query is a query you are executing, assume someModel is a mongo model for the id you are looking for, and finally assume results.idList is the field you are looking for your object id in.

   var array ={ return v.toString(); });
   var exists = array.indexOf(someModel._id.toString()) >= 0;

How to Update Multiple Array Elements in mongodb

With the release of MongoDB 3.6 ( and available in the development branch from MongoDB 3.5.12 ) you can now update multiple array elements in a single request.

This uses the filtered positional $[<identifier>] update operator syntax introduced in this version:

  { "events.profile":10 },
  { "$set": { "events.$[elem].handled": 0 } },
  { "arrayFilters": [{ "elem.profile": 10 }], "multi": true }

The "arrayFilters" as passed to the options for .update() or even .updateOne(), .updateMany(), .findOneAndUpdate() or .bulkWrite() method specifies the conditions to match on the identifier given in the update statement. Any elements that match the condition given will be updated.

Noting that the "multi" as given in the context of the question was used in the expectation that this would "update multiple elements" but this was not and still is not the case. It's usage here applies to "multiple documents" as has always been the case or now otherwise specified as the mandatory setting of .updateMany() in modern API versions.

NOTE Somewhat ironically, since this is specified in the "options" argument for .update() and like methods, the syntax is generally compatible with all recent release driver versions.

However this is not true of the mongo shell, since the way the method is implemented there ( "ironically for backward compatibility" ) the arrayFilters argument is not recognized and removed by an internal method that parses the options in order to deliver "backward compatibility" with prior MongoDB server versions and a "legacy" .update() API call syntax.

So if you want to use the command in the mongo shell or other "shell based" products ( notably Robo 3T ) you need a latest version from either the development branch or production release as of 3.6 or greater.

See also positional all $[] which also updates "multiple array elements" but without applying to specified conditions and applies to all elements in the array where that is the desired action.

Also see Updating a Nested Array with MongoDB for how these new positional operators apply to "nested" array structures, where "arrays are within other arrays".

IMPORTANT - Upgraded installations from previous versions "may" have not enabled MongoDB features, which can also cause statements to fail. You should ensure your upgrade procedure is complete with details such as index upgrades and then run

   db.adminCommand( { setFeatureCompatibilityVersion: "3.6" } )

Or higher version as is applicable to your installed version. i.e "4.0" for version 4 and onwards at present. This enabled such features as the new positional update operators and others. You can also check with:

   db.adminCommand( { getParameter: 1, featureCompatibilityVersion: 1 } )

To return the current setting

MongoDB what are the default user and password?

In addition with what @Camilo Silva already mentioned, if you want to give free access to create databases, read, write databases, etc, but you don't want to create a root role, you can change the 3rd step with the following:

use admin
    user: "myUserAdmin",
    pwd: "abc123",
    roles: [ { role: "userAdminAnyDatabase", db: "admin" }, 
             { role: "dbAdminAnyDatabase", db: "admin" }, 
             { role: "readWriteAnyDatabase", db: "admin" } ]

Visually managing MongoDB documents and collections

MongoVue is the best I found till now, it has great features like database or collection copy and text mode viewing for records which is extremely useful

How do you rename a MongoDB database?

No there isn't. See

Unfortunately, this is not an simple feature for us to implement due to the way that database metadata is stored in the original (default) storage engine. In MMAPv1 files, the namespace (e.g.: dbName.collection) that describes every single collection and index includes the database name, so to rename a set of database files, every single namespace string would have to be rewritten. This impacts:

  • the .ns file
  • every single numbered file for the collection
  • the namespace for every index
  • internal unique names of each collection and index
  • contents of system.namespaces and system.indexes (or their equivalents in the future)
  • other locations I may be missing

This is just to accomplish a rename of a single database in a standalone mongod instance. For replica sets the above would need to be done on every replica node, plus on each node every single oplog entry that refers this database would have to be somehow invalidated or rewritten, and then if it's a sharded cluster, one also needs to add these changes to every shard if the DB is sharded, plus the config servers have all the shard metadata in terms of namespaces with their full names.

There would be absolutely no way to do this on a live system.

To do it offline, it would require re-writing every single database file to accommodate the new name, and at that point it would be as slow as the current "copydb" command...

How to use mongoose findOne

You might want to consider using console.log with the built-in "arguments" object:

console.log(arguments); // would have shown you [0] null, [1] yourResult

This will always output all of your arguments, no matter how many arguments you have.

How to remove array element in mongodb?

This below code will remove the complete object element from the array, where the phone number is '+1786543589455'

  { _id: id },
  { $pull: { 'contact': { number: '+1786543589455' } } }

Error: getaddrinfo ENOTFOUND in nodejs for get call

I also had same problem and I fixed it by using right proxy. Please double check your proxy settings if you are using proxy network.

Hope this will help you -

Populate nested array in mongoose

That works for me:

  .populate({ path: 'pages' })
  .exec(function(err, docs) {

    var options = {
      path: 'pages.components',
      model: 'Component'

    if (err) return res.json(500);
    Project.populate(docs, options, function (err, projects) {

Documentation: Model.populate

MongoDB query with an 'or' condition

MongoDB query with an 'or' condition


MongoDB query with an 'or', 'and', condition combined.


MongoDB: Server has startup warnings ''Access control is not enabled for the database''

Mongodb v3.4

You need to do the following to create a secure database:

Make sure the user starting the process has permissions and that the directories exist (/data/db in this case).

1) Start MongoDB without access control.

mongod --port 27017 --dbpath /data/db

2) Connect to the instance.

mongo --port 27017

3) Create the user administrator (in the admin authentication database).

use admin
    user: "myUserAdmin",
    pwd: "abc123",
    roles: [ { role: "userAdminAnyDatabase", db: "admin" } ]

4) Re-start the MongoDB instance with access control.

mongod --auth --port 27017 --dbpath /data/db

5) Connect and authenticate as the user administrator.

mongo --port 27017 -u "myUserAdmin" -p "abc123" --authenticationDatabase "admin"

6) Create additional users as needed for your deployment (e.g. in the test authentication database).

use test
    user: "myTester",
    pwd: "xyz123",
    roles: [ { role: "readWrite", db: "test" },
             { role: "read", db: "reporting" } ]

7) Connect and authenticate as myTester.

mongo --port 27017 -u "myTester" -p "xyz123" --authenticationDatabase "test"

I basically just explained the short version of the official docs here:

Create an ISO date object in javascript

Try using the ISO string

var isodate = new Date().toISOString()

See also: method definition at MDN.

Unable to create/open lock file: /data/mongod.lock errno:13 Permission denied

For mac users:
Run ls -ld /data/db/
Output should be something like drwrx-xr-x 20 singh wheel 680 21 Jul 05:49 /data/db/
Where singh is the owner and wheel is the group it belongs to.
Run sudo chown -R singh:wheel /data/db
Run mongod

MongoDb query condition on comparing 2 fields

You can use $expr ( 3.6 mongo version operator ) to use aggregation functions in regular query.

Compare query operators vs aggregation comparison operators.

Regular Query:

db.T.find({$expr:{$gt:["$Grade1", "$Grade2"]}})

Aggregation Query:

db.T.aggregate({$match:{$expr:{$gt:["$Grade1", "$Grade2"]}}})

mongodb: insert if not exists

In general, using update is better in MongoDB as it will just create the document if it doesn't exist yet, though I'm not sure how to work that with your python adapter.

Second, if you only need to know whether or not that document exists, count() which returns only a number will be a better option than find_one which supposedly transfer the whole document from your MongoDB causing unnecessary traffic.

return query based on date

Just been implementing something similar in Mongo v3.2.3 using Node v0.12.7 and v4.4.4 and used:

{ $gte: new Date(dateVar).toISOString() }

I'm passing in an ISODate (e.g. 2016-04-22T00:00:00Z) and this works for a .find() query with or without the toISOString function. But when using in an .aggregate() $match query it doesn't like the toISOString function!

Date query with ISODate in mongodb doesn't seem to work

In json strict mode, you'll have to keep the order:

    "dt": {
        "$gte": {
            "$date": "2013-10-01T00:00:00.000Z"

Only thing which worked to define my search queries on


If you need multiple columns to group by, follow this model. Here I am conducting a count by status and type:

    "$group": {
        _id: {
            status: "$status",
            type: "$type"
        count: {
            $sum: 1

Printing Mongo query output to a file while in the mongo shell

Combining several conditions:

  • write mongo query in JS file and send it from terminal
  • switch/define a database programmatically
  • output all found records
  • cut initial output lines
  • save the output into JSON file


// Switch current database to "mydatabase"
db = db.getSiblingDB('mydatabase');

// The mark for cutting initial output off

// Main output
// "toArray()" method allows to get all records
printjson( db.getCollection('jobs').find().toArray() );

Sending the query from terminal

-z key of sed allows treat output as a single multi-line string

$> mongo localhost --quiet myScriptFile.js | sed -z 's/^.*CUT_TO_HERE\n//' > output.json

When to Redis? When to MongoDB?

If your project budged allows you to have enough RAM memory on your environment - answer is Redis. Especially taking in account new Redis 3.2 with cluster functionality.

MongoDB and "joins"

The database does not do joins -- or automatic "linking" between documents. However you can do it yourself client side. If you need to do 2, that is ok, but if you had to do 2000, the number of client/server turnarounds would make the operation slow.

In MongoDB a common pattern is embedding. In relational when normalizing things get broken into parts. Often in mongo these pieces end up being a single document, so no join is needed anyway. But when one is needed, one does it client-side.

Consider the classic ORDER, ORDER-LINEITEM example. One order and 8 line items are 9 rows in relational; in MongoDB we would typically just model this as a single BSON document which is an order with an array of embedded line items. So in that case, the join issue does not arise. However the order would have a CUSTOMER which probably is a separate collection - the client could read the cust_id from the order document, and then go fetch it as needed separately.

There are some videos and slides for schema design talks on the web site I belive.

Formatting ISODate from Mongodb

you can use mongo query like this yearMonthDayhms: { $dateToString: { format: "%Y-%m-%d-%H-%M-%S", date: {$subtract:["$cdt",14400000]}}}

HourMinute: { $dateToString: { format: "%H-%M-%S", date: {$subtract:["$cdt",14400000]}}}

enter image description here

Find document with array that contains a specific value

I know this topic is old, but for future people who could wonder the same question, another incredibly inefficient solution could be to do:

PersonModel.find({$where : 'this.favouriteFoods.indexOf("sushi") != -1'});

This avoids all optimisations by MongoDB so do not use in production code.

How to query MongoDB with "like"?

Just in case, someone is looking for a sql LIKE kind of query for a key that holds an Array of Strings instead of a String, here it is:

db.users.find({"name": {$in: [/.*m.*/]}})

Referencing another schema in Mongoose

It sounds like the populate method is what your looking for. First make small change to your post schema:

var postSchema = new Schema({
    name: String,
    postedBy: {type: mongoose.Schema.Types.ObjectId, ref: 'User'},
    dateCreated: Date,
    comments: [{body:"string", by: mongoose.Schema.Types.ObjectId}],

Then make your model:

var Post = mongoose.model('Post', postSchema);

Then, when you make your query, you can populate references like this:

Post.findOne({_id: 123})
.exec(function(err, post) {
    // do stuff with post

What is the correct way to start a mongod service on linux / OS X?

With recent builds of mongodb community edition, this is straightforward.

When you install via brew, it tells you what exactly to do. There is no need to create a new launch control file.

$ brew install mongodb
==> Downloading ### 100.0%
==> Pouring mongodb-3.0.6.yosemite.bottle.tar.gz
==> Caveats
To have launchd start mongodb at login:
  ln -sfv /usr/local/opt/mongodb/*.plist ~/Library/LaunchAgents
Then to load mongodb now:
  launchctl load ~/Library/LaunchAgents/homebrew.mxcl.mongodb.plist
Or, if you don't want/need launchctl, you can just run:
  mongod --config /usr/local/etc/mongod.conf
==> Summary
  /usr/local/Cellar/mongodb/3.0.6: 17 files, 159M

Cannot access mongodb through browser - It looks like you are trying to access MongoDB over HTTP on the native driver port

I am in ubuntu 14.04 and mongod is registered as an upstart service. The answers in this post sent me in the right direction. The only adaptation I had to do to make things work with the upstart service was to edit /etc/mongod.conf. Look for the lines that read:

# Enable the HTTP interface (Defaults to port 28017).
# httpinterface = true

Just remove the # in front of httpinterface and restart the mongod service:

sudo restart mongod

Note: You can also enable the rest interface by adding a line that reads rest=true right below the httpinterface line mentioned above.

Is there a way to 'pretty' print MongoDB shell output to a file?

Using this answer from Asya Kamsky, I wrote a one-line bat script for Windows. The line looks like this:

mongo --quiet %1 --eval "printjson(db.%2.find().toArray())" > output.json

Then one can run it:

exportToJson.bat DbName CollectionName

Couldn't connect to server

The log indicates that mongodb is terminating because there is an old lock file.

If you are not and were not running with journaling, remove the lock file, run repair, and start mongodb again.

If you are or were running with journaling turned on, see the relevant Mongo DB docs. Note that they say "If you are running with Journaling you should not do a repair to recover to a consistent state." So if you were journaling, the repair may have made things worse.

How to enable authentication on MongoDB through Docker?

The Dockerfile for the official mongo image is here. The default command is mongod but you can override to add the --auth switch assuming user's are already configured.

docker run -d .... mongodb:latest mongod --auth

If the user has to be created then you need to volume mount a startup script into / to replace the default startup script and then have that script create users and start mongo with the auth switch.

docker run -d .... -v $PWD/ mongodb:latest

How can I list all collections in the MongoDB shell?

For MongoDB 3.0 deployments using the WiredTiger storage engine, if you run db.getCollectionNames() from a version of the mongo shell before 3.0 or a version of the driver prior to 3.0 compatible version, db.getCollectionNames() will return no data, even if there are existing collections.

For further details, please refer to this.

Auto increment in MongoDB to store sequence of Unique User ID

You can, but you should not

Each object in mongo already has an id, and they are sortable in insertion order. What is wrong with getting collection of user objects, iterating over it and use this as incremented ID? Er go for kind of map-reduce job entirely

mongodb service is not starting up

Removing the .lock file and reinstalling did not solve the issue on my machine (Ubuntu 19.10). The problem was that after unexpected shutdown, the MongoDB sock does not belong to the MongoDB group and user anymore.

So, I follow the steps below:

  1. cd /tmp
  2. ls *.sock
  3. Change the user:group permission:

    chown mongodb:mongodb <YOUR_SOCK>
  4. sudo systemctl start mongod

  5. sudo systemctl status mongod

How do I partially update an object in MongoDB so the new object will overlay / merge with the existing one

I had success doing it this way:

db.collection.update(  { _id:...} , { $set: { 'key.another_key' : new_info  } } );

I have a function that handles my profile updates dynamically

function update(prop, newVal) {
  const str = `profile.${prop}`;
  db.collection.update( { _id:...}, { $set: { [str]: newVal } } );

Note: 'profile' is specific to my implementation, it is just the string of the key that you would like to modify.

Mongoose, update values in array of objects

I had similar issues. Here is the cleanest way to do it.

    const personQuery = {
       _id: 1  

    const itemID = 2;

    Person.findOne(personQuery).then(item => {
       const audioIndex = =>;
       item.items[audioIndex].name = 'Name value';;

Is mongodb running?

I know this is for php, but I got here looking for a solution for node. Using mongoskin:

mongodb.admin().ping(function(err) {
    if(err === null)
        // true - you got a conntion, congratulations
    else if(err.message.indexOf('failed to connect') !== -1)
        // false - database isn't around
        // actual error, do something about it

With other drivers, you can attempt to make a connection and if it fails, you know the mongo server's down. Mongoskin needs to actually make some call (like ping) because it connects lazily. For php, you can use the try-to-connect method. Make a script!


$dbIsRunning = true
try {
  $m = new MongoClient('localhost:27017');
} catch($e) {
  $dbIsRunning = false

Cannot find module '../build/Release/bson'] code: 'MODULE_NOT_FOUND' } js-bson: Failed to load c++ bson extension, using pure JS version

I tried this in mongo-sync version 4.1.2

but they made some changes and it is not working with the solutions provided here

the solution which worked for me

Path node_modules/mongo-sync/node_modules/bson/ext/index.js

Old Code

try {
    // Load the precompiled win32 binary
    if (process.platform == "win32" && process.arch == "x64") {
        bson = require('./win32/x64/bson');
    } else if (process.platform == "win32" && process.arch == "ia32") {
        bson = require('./win32/ia32/bson');
    } else {
        bson = require('../build/Release/bson');
} catch (err) {
    // Attempt to load the release bson version
    try {
        bson = require('../build/Release/bson');
    } catch (err) {
        console.error("js-bson: Failed to load c++ bson extension, using pure JS version");
        bson = require('../lib/bson/bson');

Change in the try block (copy the bson initialization from catch block)

bson = require('../lib/bson/bson');

So it will look like

try {
    // Load the precompiled win32 binary
    if(process.platform == "win32" && process.arch == "x64") {
      bson = require('./win32/x64/bson');  
    } else if(process.platform == "win32" && process.arch == "ia32") {
      bson = require('./win32/ia32/bson');  
    } else {
      bson = require('../build/Release/bson');  
} catch(err) {
    // Attempt to load the release bson version
    try {
        bson = require('../lib/bson/bson');
    } catch (err) {
        console.error("js-bson: Failed to load c++ bson extension, using pure JS version");
        bson = require('../lib/bson/bson');

Properly close mongoose's connection once you're done

You will get an error if you try to close/disconnect outside of the method. The best solution is to close the connection in both callbacks in the method. The dummy code is here.

const newTodo = new Todo({text:'cook dinner'}); => {
  console.log('todo saved',docs);
},(e) => {
  console.log('unable to save');

When to use MongoDB or other document oriented database systems?

to store this unstructured data

As you said, MongoDB is best suitable to store unstructured data. And this can organize your data into document format. These RDBMS altenatives called NoSQL data stores (MongoDB, CouchDB, Voldemort) are very useful for applications that scales massively and require faster data access from these big data stores.

And the implementation of these databases are simpler than the regular RDBMS. Since these are simple key-valued or document style binary objects directly serialized into disk. These data stores don't enforce the ACID properties, and any schemas. This doesn't provide any transaction abilities. So this can scale big and we can achieve faster access (both read and write).

But in contrast, RDBM enforces ACID and schemas on datas. If you wanted to work with structured data you can go ahead with RDBM.

I would choose MySQL for creating forums for this kind of stuff. Because this is not going to scale big. And this is a very simple (common) application which has structured relations among the data.

How do I update/upsert a document in Mongoose?

I just came back to this issue after a while, and decided to publish a plugin based on the answer by Aaron Mast.

Use it as a mongoose plugin. It sets up a static method which will recursively merge the object passed in.

Model.upsert({unique: 'value'}, updateObject});

How to remove a field completely from a MongoDB document?

you can also do this in aggregation by using project at 3.4

{$project: {"tags.words": 0} }

New to MongoDB Can not run command mongo

This worked for me (if it applies that you also see the lock file):

first>youridhere@ubuntu:/var/lib/mongodb$ sudo service mongodb start 
then >youridhere@ubuntu:/var/lib/mongodb$ sudo rm mongod.lock*

Connection refused to MongoDB errno 111

In my case previous version was 3.2. I have upgraded to 3.6 but data files was not compatible to new version so I removed all data files as it was not usable for me and its works.

You can check logs using /var/log/mongodb

Mongoose: Get full list of users

There was the very easy way to list your data :

server.get('/userlist' , function (req , res) {
 User.find({}).then(function (users) {

Server Discovery And Monitoring engine is deprecated

Add the useUnifiedTopology option and set it to true.

Set other 3 configuration of the mongoose.connect options which will deal with other remaining DeprecationWarning.

This configuration works for me!

const url = 'mongodb://localhost:27017/db_name';
        useNewUrlParser: true, 
        useUnifiedTopology: true,
        useCreateIndex: true,
        useFindAndModify: false

This will solve 4 DeprecationWarning.

  1. Current URL string parser is deprecated, and will be removed in a future version. To use the new parser, pass option { useNewUrlParser: true } to MongoClient.connect.
  2. Current Server Discovery and Monitoring engine is deprecated, and will be removed in a future version. To use the new Server Discover and Monitoring engine, pass option { useUnifiedTopology: true } to the MongoClient constructor.
  3. Collection.ensureIndex is deprecated. Use createIndexes instead.
  4. DeprecationWarning: Mongoose: findOneAndUpdate() and findOneAndDelete() without the useFindAndModify option set to false are deprecated. See:

Hope it helps.

Redirect output of mongo query to a csv file

Mongo's in-built export is working fine, unless you want to any data manipulation like format date, covert data types etc.

Following command works as charm.

    mongoexport -h localhost -d databse -c collection --type=csv 
    --fields erpNum,orderId,time,status 
    -q '{"time":{"$gt":1438275600000}, "status":{"$ne" :"Cancelled"}}' 
    --out report.csv

How to update values using pymongo?

in python the operators should be in quotes: db.ProductData.update({'fromAddress':'http://localhost:7000/'}, {"$set": {'fromAddress': 'http://localhost:5000/'}},{"multi": True})

sudo service mongodb restart gives "unrecognized service error" in ubuntu 14.0.4

You need to make sure the file (ex. /etc/init.d/mongodb) has execute permissions.

chmod +x /etc/init.d/mongodb

BadValue Invalid or no user locale set. Please ensure LANG and/or LC_* environment variables are set correctly

Amazon Linux AMI

Permanent solution for ohmyzsh:

$ vim ~/.zshrc

Write there below:

export LC_ALL=en_US.UTF-8
export LANG=en_US.UTF-8
export LANGUAGE=en_US.UTF-8

Update changes in current shell by: $ source ~/.zshrc

How can I generate an ObjectId with mongoose?

I needed to generate mongodb ids on client side.

After digging into the mongodb source code i found they generate ObjectIDs using npm bson lib.

If ever you need only to generate an ObjectID without installing the whole mongodb / mongoose package, you can import the lighter bson library :

const bson = require('bson');
new bson.ObjectId(); // 5cabe64dcf0d4447fa60f5e2

Note: There is also an npm project named bson-objectid being even lighter

Retrieve only the queried element in an object array in MongoDB collection

Another interesing way is to use $redact, which is one of the new aggregation features of MongoDB 2.6. If you are using 2.6, you don't need an $unwind which might cause you performance problems if you have large arrays.

    { $match: { 
         shapes: { $elemMatch: {color: "red"} } 
    { $redact : {
         $cond: {
             if: { $or : [{ $eq: ["$color","red"] }, { $not : "$color" }]},
             then: "$$DESCEND",
             else: "$$PRUNE"

$redact "restricts the contents of the documents based on information stored in the documents themselves". So it will run only inside of the document. It basically scans your document top to the bottom, and checks if it matches with your if condition which is in $cond, if there is match it will either keep the content($$DESCEND) or remove($$PRUNE).

In the example above, first $match returns the whole shapes array, and $redact strips it down to the expected result.

Note that {$not:"$color"} is necessary, because it will scan the top document as well, and if $redact does not find a color field on the top level this will return false that might strip the whole document which we don't want.

How to retrieve the last autoincremented ID from a SQLite table?

Sample code from @polyglot solution

SQLiteCommand sql_cmd;
sql_cmd.CommandText = "select seq from sqlite_sequence where name='myTable'; ";
int newId = Convert.ToInt32( sql_cmd.ExecuteScalar( ) );

Error: 'int' object is not subscriptable - Python

x is already integer(x=0) and again you trying to make x again integer and also you gave indexing which is beyound the limit because x already has only one indexing (0) and you are trying to give indexing same as age so thats why you get this error. use this simple code

name1 = input("What's your name? ")
age1 = int(input ("how old are you?" ))
twentyone = str(21-age1)
print("Hi, " +name1+ " you will be 21 in: " + twentyone + " years.")

How to merge remote master to local branch

I found out it was:

$ git fetch upstream
$ git merge upstream/master

Fragment onCreateView and onActivityCreated called twice

I have had the same problem with a simple Activity carrying only one fragment (which would get replaced sometimes). I then realized I use onSaveInstanceState only in the fragment (and onCreateView to check for savedInstanceState), not in the activity.

On device turn the activity containing the fragments gets restarted and onCreated is called. There I did attach the required fragment (which is correct on the first start).

On the device turn Android first re-created the fragment that was visible and then called onCreate of the containing activity where my fragment was attached, thus replacing the original visible one.

To avoid that I simply changed my activity to check for savedInstanceState:

protected void onCreate(Bundle savedInstanceState) {

if (savedInstanceState != null) {
/**making sure you are not attaching the fragments again as they have 
 *already added
  // following code to attach fragment initially


I did not even Overwrite onSaveInstanceState of the activity.

Detect If Browser Tab Has Focus

Surprising to see nobody mentioned document.hasFocus

if (document.hasFocus()) console.log('Tab is active')

MDN has more information.

Limit number of characters allowed in form input text field

<input type="text" maxlength="5">

the maximum amount of letters that can be in the input is 5.

Generate PDF from Swagger API documentation

You can modify your REST project, so as to produce the needed static documents (html, pdf etc) upon building the project.

If you have a Java Maven project you can use the pom snippet below. It uses a series of plugins to generate a pdf and an html documentation (of the project's REST resources).

  1. rest-api -> swagger.json : swagger-maven-plugin
  2. swagger.json -> Asciidoc : swagger2markup-maven-plugin
  3. Asciidoc -> PDF : asciidoctor-maven-plugin

Please be aware that the order of execution matters, since the output of one plugin, becomes the input to the next:

                    <title>Put your REST service's name here</title>
                    <description>Add some description</description>
            <!-- fx process-classes phase -->
        <!-- specify location to place asciidoc files -->
        <!-- You will need to create an .adoc file. This is the input to this plugin -->
            <!-- this path is referenced in swagger.adoc file. The given file will simply 
                point to the previously create adoc files/assemble them. -->
                <!-- specify location to place html file -->
                <!-- specify location to place pdf file -->

The asciidoctor plugin assumes the existence of an .adoc file to work on. You can create one that simply collects the ones that were created by the swagger2markup plugin:


If you want your generated html document to become part of your war file you have to make sure that it is present on the top level - static files in the WEB-INF folder will not be served. You can do this in the maven-war-plugin:

            <!-- Add swagger.pdf to WAR file, so as to make it available as static content. -->
            <!-- Add swagger.html to WAR file, so as to make it available as static content. -->

The war plugin works on the generated documentation - as such, you must make sure that those plugins have been executed in an earlier phase.

Access parent DataContext from DataTemplate

I had problems with the relative source in Silverlight. After searching and reading I did not find a suitable solution without using some additional Binding library. But, here is another approach for gaining access to the parent DataContext by directly referencing an element of which you know the data context. It uses Binding ElementName and works quite well, as long as you respect your own naming and don't have heavy reuse of templates/styles across components:

<ItemsControl x:Name="level1Lister" ItemsSource={Binding MyLevel1List}>
      <Button Content={Binding MyLevel2Property}
              Command={Binding ElementName=level1Lister,
              CommandParameter={Binding MyLevel2Property}>

This also works if you put the button into Style/Template:

  <Style x:Key="buttonStyle" TargetType="Button">
    <Setter Property="Template">
        <ControlTemplate TargetType="Button">
          <Button Command={Binding ElementName=level1Lister,
                  CommandParameter={Binding MyLevel2Property}>

<ItemsControl x:Name="level1Lister" ItemsSource={Binding MyLevel1List}>
      <Button Content="{Binding MyLevel2Property}" 
              Style="{StaticResource buttonStyle}"/>

At first I thought that the x:Names of parent elements are not accessible from within a templated item, but since I found no better solution, I just tried, and it works fine.

How to solve 'Redirect has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header'?

When you have this problem with Chrome, you don't need an Extension.
Start Chrome from the Console:

chrome.exe --user-data-dir="C:/Chrome dev session" --disable-web-security

Maybe you have to close all Tabs in Chrome and restart it.

Concat scripts in order with Gulp

The sort-stream may also be used to ensure specific order of files with gulp.src. Sample code that puts the backbone.js always as the last file to process:

var gulp = require('gulp');
var sort = require('sort-stream');
gulp.task('scripts', function() {
gulp.src(['./source/js/*.js', './source/js/**/*.js'])
  .pipe(sort(function(a, b){
    aScore = a.path.match(/backbone.js$/) ? 1 : 0;
    bScore = b.path.match(/backbone.js$/) ? 1 : 0;
    return aScore - bScore;

Python: tf-idf-cosine: to find document similarity

Let me give you another tutorial written by me. It answers your question, but also makes an explanation why we are doing some of the things. I also tried to make it concise.

So you have a list_of_documents which is just an array of strings and another document which is just a string. You need to find such document from the list_of_documents that is the most similar to document.

Let's combine them together: documents = list_of_documents + [document]

Let's start with dependencies. It will become clear why we use each of them.

from nltk.corpus import stopwords
import string
from nltk.tokenize import wordpunct_tokenize as tokenize
from nltk.stem.porter import PorterStemmer
from sklearn.feature_extraction.text import TfidfVectorizer
from scipy.spatial.distance import cosine

One of the approaches that can be uses is a bag-of-words approach, where we treat each word in the document independent of others and just throw all of them together in the big bag. From one point of view, it looses a lot of information (like how the words are connected), but from another point of view it makes the model simple.

In English and in any other human language there are a lot of "useless" words like 'a', 'the', 'in' which are so common that they do not possess a lot of meaning. They are called stop words and it is a good idea to remove them. Another thing that one can notice is that words like 'analyze', 'analyzer', 'analysis' are really similar. They have a common root and all can be converted to just one word. This process is called stemming and there exist different stemmers which differ in speed, aggressiveness and so on. So we transform each of the documents to list of stems of words without stop words. Also we discard all the punctuation.

porter = PorterStemmer()
stop_words = set(stopwords.words('english'))

modified_arr = [[porter.stem(i.lower()) for i in tokenize(d.translate(None, string.punctuation)) if i.lower() not in stop_words] for d in documents]

So how will this bag of words help us? Imagine we have 3 bags: [a, b, c], [a, c, a] and [b, c, d]. We can convert them to vectors in the basis [a, b, c, d]. So we end up with vectors: [1, 1, 1, 0], [2, 0, 1, 0] and [0, 1, 1, 1]. The similar thing is with our documents (only the vectors will be way to longer). Now we see that we removed a lot of words and stemmed other also to decrease the dimensions of the vectors. Here there is just interesting observation. Longer documents will have way more positive elements than shorter, that's why it is nice to normalize the vector. This is called term frequency TF, people also used additional information about how often the word is used in other documents - inverse document frequency IDF. Together we have a metric TF-IDF which have a couple of flavors. This can be achieved with one line in sklearn :-)

modified_doc = [' '.join(i) for i in modified_arr] # this is only to convert our list of lists to list of strings that vectorizer uses.
tf_idf = TfidfVectorizer().fit_transform(modified_doc)

Actually vectorizer allows to do a lot of things like removing stop words and lowercasing. I have done them in a separate step only because sklearn does not have non-english stopwords, but nltk has.

So we have all the vectors calculated. The last step is to find which one is the most similar to the last one. There are various ways to achieve that, one of them is Euclidean distance which is not so great for the reason discussed here. Another approach is cosine similarity. We iterate all the documents and calculating cosine similarity between the document and the last one:

l = len(documents) - 1
for i in xrange(l):
    minimum = (1, None)
    minimum = min((cosine(tf_idf[i].todense(), tf_idf[l + 1].todense()), i), minimum)
print minimum

Now minimum will have information about the best document and its score.

Dart SDK is not configured

I am using Win10 Pro;

If you are using Android Studio and getting this message 'Error: Dart SDK is not found in specified location',

My fix was this.

  1. Go to File/Settings or Ctrl+Alt+S to bring up the settings window.
  2. Go down to 'Language & Frameworks and click on Dart
  3. Check Enable Dart support for the project 'YOUR_PROJECT_NAME'
  4. For the Path Dart SDK path: enter the location where you are storing the flutter directory.
  5. Drill down that directory till you see the Dart SDK directory C:\flutter\bin\cache\dart-sdk. You can also Check SDK update by checking the box and clicking on Check now to get the latest version.

This worked for me.

Visual Studio build fails: unable to copy exe-file from obj\debug to bin\debug

When I have come across this problem it is to do with the Fact that the project I am trying to build is set as the Startup project in the solution making the .exe in the obj folder locked ( it also appears in your task manager,) right click another project in your solution and choose set startup project. This will release the lock, remove it from task manager and should let you build.

How can I get a resource content from a static context?

I load shader for openGL ES from static function.

Remember you must use lower case for your file and directory name, or else the operation will be failed

public class MyGLRenderer implements GLSurfaceView.Renderer {


    public static int loadShader() {
        //    Read file as input stream
        InputStream inputStream = MyGLRenderer.class.getResourceAsStream("/res/raw/vertex_shader.txt");

        //    Convert input stream to string
        Scanner s = new Scanner(inputStream).useDelimiter("\\A");
        String shaderCode = s.hasNext() ? : "";



How to implement class constructor in Visual Basic?

Not sure what you mean with "class constructor" but I'd assume you mean one of the ones below.

Instance constructor:

Public Sub New()

End Sub

Shared constructor:

Shared Sub New()

End Sub

How to check if a column exists in a SQL Server table?

Try this...

    [TABLE_NAME] = 'Employees'
    AND [COLUMN_NAME] = 'EmployeeID')
  ALTER TABLE [Employees]
    ADD [EmployeeID] INT NULL

how to call url of any other website in php

As other's have mentioned, PHP's cURL functions will allow you to perform advanced HTTP requests. You can also use file_get_contents to access REST APIs:

$payload = file_get_contents('');

Starting with PHP 5 you can also create a stream context which will allow you to change headers or post data to the service.

Android Studio - Auto complete and other features not working

  1. Close Android Studio

  2. Go to c_users_path_on_windows/.AndroidStudio3.5/system/

  3. Delete the cache folder

  4. Start Android Studio

    This works for me.

How to install Visual C++ Build tools?

The current version (2019/03/07) is Build Tools for Visual Studio 2017. It's an online installer, you need to include at least the individual components:

  • VC++ 2017 version xx.x tools
  • Windows SDK to use standard libraries.

Print text in Oracle SQL Developer SQL Worksheet window

You could put your text in a select statement such as...

SELECT 'Querying Table1' FROM dual;

How to force div to appear below not next to another?

what u can also do i place an extra "dummy" div before your last div.

Make it 1 px heigh and the width as much needed to cover the container div/body

This will make the last div appear under it, starting from the left.

How to find memory leak in a C++ code/project?

AddressSanitizer (ASan) is a fast memory error detector. It finds use-after-free and {heap,stack,global}-buffer overflow bugs in C/C++ programs. It finds:

  • Use after free (dangling pointer dereference)
  • Heap buffer overflow
  • Stack buffer overflow
  • Global buffer overflow
  • Use after return
  • Initialization order bugs

This tool is very fast. The average slowdown of the instrumented program is ~2x.

Can you write nested functions in JavaScript?

Not only can you return a function which you have passed into another function as a variable, you can also use it for calculation inside but defining it outside. See this example:

    function calculate(a,b,fn) {
      var c = a * 3 + b + fn(a,b);
      return  c;

    function sum(a,b) {
      return a+b;

    function product(a,b) {
      return a*b;

    document.write(calculate (10,20,sum)); //80
    document.write(calculate (10,20,product)); //250

Awaiting multiple Tasks with different results

In case you are trying to log all errors make sure you keep Task.WhenAll line in your code, lot of comments suggest that you can remove it and wait for individual tasks. Task.WhenAll is really important for error handling. Without this line you potentially leaving your code open for unobserved exceptions.

var catTask = FeedCat();
var houseTask = SellHouse();
var carTask = BuyCar();

await Task.WhenAll(catTask, houseTask, carTask);

var cat = await catTask;
var house = await houseTask;
var car = await carTask;

Imagine FeedCat throws exception in the following code:

var catTask = FeedCat();
var houseTask = SellHouse();
var carTask = BuyCar();

var cat = await catTask;
var house = await houseTask;
var car = await carTask;

In that case you will never await on houseTask nor carTask. There are 3 possible scenarios here:

  1. SellHouse is already completed successfully when FeedCat failed. In this case you are fine.

  2. SellHouse is not complete and fails with exception at some point. Exception is not observed and will be rethrown on finalizer thread.

  3. SellHouse is not complete and contains awaits inside it. In case your code runs in ASP.NET SellHouse will fail as soon as some of the awaits will completed inside it. This happens because you basically made fire & forget call and synchronization context was lost as soon as FeedCat failed.

Here is error that you will get for case (3):

System.AggregateException: A Task's exception(s) were not observed either by Waiting on the Task or accessing its Exception property. As a result, the unobserved exception was rethrown by the finalizer thread. ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Web.ThreadContext.AssociateWithCurrentThread(Boolean setImpersonationContext)
   at System.Web.HttpApplication.OnThreadEnterPrivate(Boolean setImpersonationContext)
   at System.Web.HttpApplication.System.Web.Util.ISyncContext.Enter()
   at System.Web.Util.SynchronizationHelper.SafeWrapCallback(Action action)
   at System.Threading.Tasks.Task.Execute()
   --- End of inner exception stack trace ---
---> (Inner Exception #0) System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Web.ThreadContext.AssociateWithCurrentThread(Boolean setImpersonationContext)
   at System.Web.HttpApplication.OnThreadEnterPrivate(Boolean setImpersonationContext)
   at System.Web.HttpApplication.System.Web.Util.ISyncContext.Enter()
   at System.Web.Util.SynchronizationHelper.SafeWrapCallback(Action action)
   at System.Threading.Tasks.Task.Execute()<---

For case (2) you will get similar error but with original exception stack trace.

For .NET 4.0 and later you can catch unobserved exceptions using TaskScheduler.UnobservedTaskException. For .NET 4.5 and later unobserved exceptions are swallowed by default for .NET 4.0 unobserved exception will crash your process.

More details here: Task Exception Handling in .NET 4.5

Is there a portable way to get the current username in Python?

You best bet would be to combine os.getuid() with pwd.getpwuid():

import os
import pwd

def get_username():
    return pwd.getpwuid( os.getuid() )[ 0 ]

Refer to the pwd docs for more details:

how to make div click-able?

If this div is a function I suggest use cursor:pointer in your style like style="cursor:pointer" and can use onclick function.

like this

<div onclick="myfunction()" style="cursor:pointer"></div>

but I suggest you use a JS framework like jquery or extjs

Where does one get the "sys/socket.h" header/source file?

Given that Windows has no sys/socket.h, you might consider just doing something like this:

#ifdef __WIN32__
# include <winsock2.h>
# include <sys/socket.h>

I know you indicated that you won't use WinSock, but since WinSock is how TCP networking is done under Windows, I don't see that you have any alternative. Even if you use a cross-platform networking library, that library will be calling WinSock internally. Most of the standard BSD sockets API calls are implemented in WinSock, so with a bit of futzing around, you can make the same sockets-based program compile under both Windows and other OS's. Just don't forget to do a

#ifdef __WIN32__
   WORD versionWanted = MAKEWORD(1, 1);
   WSADATA wsaData;
   WSAStartup(versionWanted, &wsaData);

at the top of main()... otherwise all of your socket calls will fail under Windows, because the WSA subsystem wasn't initialized for your process.

Deploying Maven project throws invalid LOC header (bad signature)

The solution for me was to run mvn with -X:

$ mvn package -X

Then look backwards through the output until you see the failure and then keep going until you see the last jar file that mvn tried to process:

... <<output ommitted>>
[DEBUG] Processing JAR /Users/snowch/.m2/repository/org/eclipse/jetty/jetty-server/9.2.15.v20160210/jetty-server-9.2.15.v20160210.jar
[INFO] ------------------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3.607 s
[INFO] Finished at: 2017-10-04T14:30:13+01:00
[INFO] Final Memory: 23M/370M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-shade-plugin:3.1.0:shade (default) on project kafka-connect-on-cloud-foundry: Error creating shaded jar: invalid LOC header (bad signature) -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.maven.plugins:maven-shade-plugin:3.1.0:shade (default) on project kafka-connect-on-cloud-foundry: Error creating shaded jar: invalid LOC header (bad signature)

Look at the last jar before it failed and remove that from the local repository, i.e.

$ rm -rf /Users/snowch/.m2/repository/org/eclipse/jetty/jetty-server/9.2.15.v20160210/

How to filter wireshark to see only dns queries that are sent/received from/by my computer?

Rather than using a DisplayFilter you could use a very simple CaptureFilter like

port 53

See the "Capture only DNS (port 53) traffic" example on the CaptureFilters wiki.

json.dumps vs flask.jsonify

This is flask.jsonify()

def jsonify(*args, **kwargs):
    if __debug__:
    return current_app.response_class(json.dumps(dict(*args, **kwargs),
        indent=None if request.is_xhr else 2), mimetype='application/json')

The json module used is either simplejson or json in that order. current_app is a reference to the Flask() object i.e. your application. response_class() is a reference to the Response() class.

What is the way of declaring an array in JavaScript?

In your first example, you are making a blank array, same as doing var x = []. The 2nd example makes an array of size 3 (with all elements undefined). The 3rd and 4th examples are the same, they both make arrays with those elements.

Be careful when using new Array().

var x = new Array(10); // array of size 10, all elements undefined
var y = new Array(10, 5); // array of size 2: [10, 5]

The preferred way is using the [] syntax.

var x = []; // array of size 0
var y = [10] // array of size 1: [1]

var z = []; // array of size 0
z[2] = 12;  // z is now size 3: [undefined, undefined, 12]

What's a clean way to stop mongod on Mac OS X?

The solutions provided by others used to work for me but is not working for me anymore, which is as below.

brew services stop mongodb
brew services start mongodb

brew services list gives

Name              Status  User      Plist
mongodb-community started XXXXXXXXX /Users/XXXXXXXXX/Library/LaunchAgents/homebrew.mxcl.mongodb-community.plist

So I used mongodb-community instead of mongodb which worked for me

brew services stop mongodb-community
brew services start mongodb-community

UIButton action in table view cell

The accepted answer using button.tag as information carrier which button has actually been pressed is solid and widely accepted but rather limited since a tag can only hold Ints.

You can make use of Swift's awesome closure-capabilities to have greater flexibility and cleaner code.

I recommend this article: How to properly do buttons in table view cells using Swift closures by Jure Zove.

Applied to your problem:

  1. Declare a variable that can hold a closure in your tableview cell like

    var buttonTappedAction : ((UITableViewCell) -> Void)?
  2. Add an action when the button is pressed that only executes the closure. You did it programmatically with cell.yes.targetForAction("connected", withSender: self) but I would prefer an @IBAction outlet :-)

    @IBAction func buttonTap(sender: AnyObject) {
  3. Now pass the content of func connected(sender: UIButton!) { ... } as a closure to cell.tapAction = {<closure content here...>}. Please refer to the article for a more precise explanation and please don't forget to break reference cycles when capturing variables from the environment.

How to get first character of string?

You can even use slice to cut-off all other characters:

x.slice(0, 1);

convert strtotime to date time format in php

$unixtime = 1307595105;
echo $time = date("m/d/Y h:i:s A T",$unixtime);


Android: Test Push Notification online (Google Cloud Messaging)

Postman is a good solution and so is php fiddle. However to avoid putting in the GCM URL and the header information every time, you can also use this nifty GCM Notification Test Tool

Safe Area of Xcode 9

I want to mention something that caught me first when I was trying to adapt a SpriteKit-based app to avoid the round edges and "notch" of the new iPhone X, as suggested by the latest Human Interface Guidelines: The new property safeAreaLayoutGuide of UIView needs to be queried after the view has been added to the hierarchy (for example, on -viewDidAppear:) in order to report a meaningful layout frame (otherwise, it just returns the full screen size).

From the property's documentation:

The layout guide representing the portion of your view that is unobscured by bars and other content. When the view is visible onscreen, this guide reflects the portion of the view that is not covered by navigation bars, tab bars, toolbars, and other ancestor views. (In tvOS, the safe area reflects the area not covered the screen's bezel.) If the view is not currently installed in a view hierarchy, or is not yet visible onscreen, the layout guide edges are equal to the edges of the view.

(emphasis mine)

If you read it as early as -viewDidLoad:, the layoutFrame of the guide will be {{0, 0}, {375, 812}} instead of the expected {{0, 44}, {375, 734}}

jQuery UI autocomplete with JSON

I understand that its been answered already. but I hope this will help someone in future and saves so much time and pain.

complete code is below: This one I did for a textbox to make it Autocomplete in CiviCRM. Hope it helps someone

CRM.$( 'input[id^=custom_78]' ).autocomplete({
            autoFill: true,
            select: function (event, ui) {
                    var label = ui.item.label;
                    var value = ui.item.value;
                    // Update subject field to add book year and book product
                    var book_year_value = CRM.$('select[id^=custom_77]  option:selected').text().replace('Book Year ','');
                    //book_year_value.replace('Book Year ','');
                    var subject_value = book_year_value + '/' + ui.item.label;
                    CRM.$( 'input[name=product_select_id]' ).val(ui.item.value);
                    return false;
            source: function(request, response) {
                    url: productUrl,
                        data: {
                                        'subCategory' : cj('select[id^=custom_77]').val(),
                                        's': request.term,
                    beforeSend: function( xhr ) {
                        xhr.overrideMimeType( "text/plain; charset=x-user-defined" );

                    success: function(result){
                                result = jQuery.parseJSON( result);
                                response(CRM.$.map(result, function (val,key) {
                                                         return {
                                                                 label: val,
                                                                 value: key
                .done(function( data ) {
                    if ( console && console.log ) {
                     // console.log( "Sample of dataas:", data.slice( 0, 100 ) );

PHP code on how I'm returning data to this jquery ajax call in autocomplete:

 * This class contains all product related functions that are called using AJAX (jQuery)
class CRM_Civicrmactivitiesproductlink_Page_AJAX {
  static function getProductList() {
        $name   = CRM_Utils_Array::value( 's', $_GET );
    $name   = CRM_Utils_Type::escape( $name, 'String' );
    $limit  = '10';

        $strSearch = "description LIKE '%$name%'";

        $subCategory   = CRM_Utils_Array::value( 'subCategory', $_GET );
    $subCategory   = CRM_Utils_Type::escape( $subCategory, 'String' );

        if (!empty($subCategory))
                $strSearch .= " AND sub_category = ".$subCategory;

        $query = "SELECT id , description as data FROM abc_books WHERE $strSearch";
        $resultArray = array();
        $dao = CRM_Core_DAO::executeQuery( $query );
        while ( $dao->fetch( ) ) {
            $resultArray[$dao->id] = $dao->data;//creating the array to send id as key and data as value
        echo json_encode($resultArray);

json_encode function: special characters

Your input has to be encoded as UTF-8 or ISO-8859-1.

Because if you try to convert an array of non-utf8 characters you'll be getting 0 as return value.

Since 5.5.0 The return value on failure was changed from null string to FALSE.

How to have image and text side by side

Use following code :


<div class='container2'>
        <div class="left">
            <img src='' class='iconDetails'>
    <div   class="right" >
    <div style="font-size:.7em;width:160px;float:left;">fine location, GPS, coarse location</div>
    <div style="float:right;font-size:.7em">0 mins ago</div>


.iconDetails {

.container2 {
.left {float:left;width:45px;}
.right {float:left;margin:0 0 0 5px;width:215px;}

How to access the ith column of a NumPy multidimensional array?

>>> test[:,0]
array([1, 3, 5])


>>> test[1,:]
array([3, 4])

lets you access rows. This is covered in Section 1.4 (Indexing) of the NumPy reference. This is quick, at least in my experience. It's certainly much quicker than accessing each element in a loop.

How can one pull the (private) data of one's own Android app?

Backed up Game data with apk. Nougat Oneplus 2.

**adb backup "-apk com.nekki.shadowfight" -f "c:\myapk\samsung2.ab"**

Using Tempdata in ASP.NET MVC - Best practice

Just be aware of TempData persistence, it's a bit tricky. For example if you even simply read TempData inside the current request, it would be removed and consequently you don't have it for the next request. Instead, you can use Peek method. I would recommend reading this cool article:

MVC Tempdata , Peek and Keep confusion

Excel - match data from one range to another and get the value from the cell to the right of the matched data

Put this formula in cell d31 and copy down to d39


Here's what is going on. VLOOKUP:

  • Takes a value (here the contents of b31),
  • Looks for it in the first column of a range (f3:f12 in the range f3:g12), and
  • Returns the value for the corresponding row in a column in that range (in this case, the 2nd column or g3:g12 of the range f3:g12).

As you know, the last argument of VLOOKUP sets the match type, with FALSE or 0 indicating an exact match.

Finally, IFERROR handles the #N/A when VLOOKUP does not find a match.

Error HRESULT E_FAIL has been returned from a call to a COM component VS2012 when debugging

I had this problem because I tried to open the SSIS Projects and test Attunity Driver for Oracle from SSDT 2013 (TFS) in SSDT 2017. In a new SSIS Project would the Attunity Driver work fine but in upgraded SSIS Project it would show the error when i try to test connection. The solution is to fix the old Project.

Why isn't my Pandas 'apply' function referencing multiple columns working?

All of the suggestions above work, but if you want your computations to by more efficient, you should take advantage of numpy vector operations (as pointed out here).

import pandas as pd
import numpy as np

df = pd.DataFrame ({'a' : np.random.randn(6),
             'b' : ['foo', 'bar'] * 3,
             'c' : np.random.randn(6)})

Example 1: looping with pandas.apply():

def my_test2(row):
    return row['a'] % row['c']

df['Value'] = df.apply(my_test2, axis=1)

The slowest run took 7.49 times longer than the fastest. This could mean that an intermediate result is being cached. 1000 loops, best of 3: 481 µs per loop

Example 2: vectorize using pandas.apply():

df['a'] % df['c']

The slowest run took 458.85 times longer than the fastest. This could mean that an intermediate result is being cached. 10000 loops, best of 3: 70.9 µs per loop

Example 3: vectorize using numpy arrays:

df['a'].values % df['c'].values

The slowest run took 7.98 times longer than the fastest. This could mean that an intermediate result is being cached. 100000 loops, best of 3: 6.39 µs per loop

So vectorizing using numpy arrays improved the speed by almost two orders of magnitude.

Which is faster: Stack allocation or Heap allocation

Never do premature assumption as other application code and usage can impact your function. So looking at function is isolation is of no use.

If you are serious with application then VTune it or use any similar profiling tool and look at hotspots.


How to send list of file in a folder to a txt file in Linux

If only names of regular files immediately contained within a directory (assume it's ~/dirs) are needed, you can do

find ~/docs -type f -maxdepth 1 > filenames.txt

How to compare datetime with only date in SQL Server

Please try this. This query can be used for date comparison

select * from [User] U where convert(varchar(10),U.DateCreated, 120) = '2014-02-07'

How do you add PostgreSQL Driver as a dependency in Maven?

From site PostgreSQL, of date 02/04/2016 (

"This is the current version of the driver. Unless you have unusual requirements (running old applications or JVMs), this is the driver you should be using. It supports Postgresql 7.2 or newer and requires a 1.6 or newer JVM. It contains support for SSL and the javax.sql package. If you are using the 1.6 then you should use the JDBC4 version. If you are using 1.7 then you should use the JDBC41 version. If you are using 1.8 then you should use the JDBC42 versionIf you are using a java version older than 1.6 then you will need to use a JDBC3 version of the driver, which will by necessity not be current"

ReportViewer Client Print Control "Unable to load client print control"?

Found a Fix:

  1. First ensure that printing is working from Report Manager (open a report in Report Manager and print from there).

  2. If it works go to Step 3, if you received the same error you need to install the following patches on the Report Server.

  3. Download and install the following update:

Transform DateTime into simple Date in Ruby on Rails

I recently wrote a gem to simplify this process and to neaten up your views, etc etc.

Check it out at:

How do I add an element to array in reducer of React native redux?

Two different options to add item to an array without mutation

case ADD_ITEM :
    return { 
        arr: [...state.arr, action.newItem]


case ADD_ITEM :
    return { 
        arr: state.arr.concat(action.newItem)

Format JavaScript date as yyyy-mm-dd

None of these answers quite satisfied me. I wanted a cross-platform solution that gave me the day in the local timezone without using any external libraries.

This is what I came up with:

function localDay(time) {
  var minutesOffset = time.getTimezoneOffset()
  var millisecondsOffset = minutesOffset*60*1000
  var local = new Date(time - millisecondsOffset)
  return local.toISOString().substr(0, 10)

That should return the day of the date, in YYYY-MM-DD format, in the timezone the date references.

So for example, localDay(new Date("2017-08-24T03:29:22.099Z")) will return "2017-08-23" even though it's already the 24th at UTC.

You'll need to polyfill Date.prototype.toISOString for it to work in Internet Explorer 8, but it should be supported everywhere else.

PHP, MySQL error: Column count doesn't match value count at row 1

The number of column parameters in your insert query is 9, but you've only provided 8 values.

INSERT INTO dbname (id, Name, Description, shortDescription, Ingredients, Method, Length, dateAdded, Username) VALUES ('', '%s', '%s', '%s', '%s', '%s', '%s', '%s')

The query should omit the "id" parameter, because it is auto-generated (or should be anyway):

INSERT INTO dbname (Name, Description, shortDescription, Ingredients, Method, Length, dateAdded, Username) VALUES ('', '%s', '%s', '%s', '%s', '%s', '%s', '%s')

Check for column name in a SqlDataReader object

To keep your code robust and clean, use a single extension function, like this:

    Public Module Extensions

        Public Function HasColumn(r As SqlDataReader, columnName As String) As Boolean

            Return If(String.IsNullOrEmpty(columnName) OrElse r.FieldCount = 0, False, Enumerable.Range(0, r.FieldCount).Select(Function(i) r.GetName(i)).Contains(columnName, StringComparer.OrdinalIgnoreCase))

        End Function

    End Module

best way to preserve numpy arrays on disk

savez() save data in a zip file, It may take some time to zip & unzip the file. You can use save() & load() function:

f = file("tmp.bin","wb"),a),b),c)

f = file("tmp.bin","rb")
aa = np.load(f)
bb = np.load(f)
cc = np.load(f)

To save multiple arrays in one file, you just need to open the file first, and then save or load the arrays in sequence.

At least one JAR was scanned for TLDs yet contained no TLDs

(tomcat 8.0.28) Above method did not work for me. This is what worked:

  1. Add this line to the end of your {CATALINA-HOME}/conf/

    org.apache.jasper.level = FINEST
  2. Shut down the server (if started).

  3. Open console and run (in case of Windows):

    %CATALINA_HOME%\bin\catalina.bat run
  4. Enjoy logs, e.g. (again, for Windows):


I gave up on integrating this with Eclipse launch configuration so be aware that this works only from console, launching the server from Eclipse won't produce additional log messages.

What does it mean if a Python object is "subscriptable" or not?

A scriptable object is an object that records the operations done to it and it can store them as a "script" which can be replayed.

For example, see: Application Scripting Framework

Now, if Alistair didn't know what he asked and really meant "subscriptable" objects (as edited by others), then (as mipadi also answered) this is the correct one:

A subscriptable object is any object that implements the __getitem__ special method (think lists, dictionaries).

Laravel 5.4 Specific Table Migration

php artisan migrate --path=/database/migrations/fileName.php

You don't have to refresh for migration because refresh means Rollback all migrations and run them all again.

Executors.newCachedThreadPool() versus Executors.newFixedThreadPool()

If you look at the source code, you will see, they are calling ThreadPoolExecutor. internally and setting their properties. You can create your one to have a better control of your requirement.

public static ExecutorService newFixedThreadPool(int nThreads) {
   return new ThreadPoolExecutor(nThreads, nThreads,0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>());

public static ExecutorService newCachedThreadPool() {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue<Runnable>());

How to undo a git pull?


Undo a merge or pull inside a dirty working tree

$ git pull           (1)
Auto-merging nitfol
Merge made by recursive.
 nitfol               |   20 +++++----
$ git reset --merge ORIG_HEAD      (2)

Even if you may have local modifications in your working tree, you can safely say git pull when you know that the change in the other branch does not overlap with them.

After inspecting the result of the merge, you may find that the change in the other branch is unsatisfactory. Running git reset --hard ORIG_HEAD will let you go back to where you were, but it will discard your local changes, which you do not want. git reset --merge keeps your local changes.

See also

Windows 7 - 'make' is not recognized as an internal or external command, operable program or batch file

I am using windows 8. I had the same problem. I added the path "C:\MinGW\bin" to system environment variable named 'path' then it worked. May be, you can try the same. Hope it'll help!

Is there an effective tool to convert C# code to Java code?

They don't convert directly, but it allows for interoperability between .NET and J2EE.

vertical-align: middle doesn't work

You must wrap your element in a table-cell, within a table using display.

Like this:

  <span class='twoline'>Two line text</span>
  <span class='float'>Float right</span>


.float {
    display: table-cell;
    vertical-align: middle;
    text-align: right;
.twoline {
    width: 50px;
    display: table-cell;
div {
    display: table;
    border: solid 1px blue;
    width: 500px;
    height: 100px;

Shown here:

What is the backslash character (\\)?

It is used to escape special characters and print them as is. E.g. to print a double quote which is used to enclose strings, you need to escape it using the backslash character.


System.out.println("printing \"this\" in quotes");


printing "this" in quotes

how to install gcc on windows 7 machine?

I use msysgit to install gcc on Windows, it has a nice installer which installs most everything that you might need. Most devs will need more than just the compiler, e.g. the shell, shell tools, make, git, svn, etc. msysgit comes with all of that.

edit: I am now using msys2. Msys2 uses pacman from Arch Linux to install packages, and includes three environments, for building msys2 apps, 32-bit native apps, and 64-bit native apps. (You probably want to build 32-bit native apps.)

You could also go full-monty and install code::blocks or some other gui editor that comes with a compiler. I prefer to use vim and make.

SQL Server equivalent to MySQL enum data type?

The best solution I've found in this is to create a lookup table with the possible values as a primary key, and create a foreign key to the lookup table.

Constructor overloading in Java - best practice

Well, here's an example for overloaded constructors.

public class Employee
   private String name;
   private int age;

   public Employee()
      System.out.println("We are inside Employee() constructor");

   public Employee(String name)
      System.out.println("We are inside Employee(String name) constructor"); = name;

   public Employee(String name, int age)
      System.out.println("We are inside Employee(String name, int age) constructor"); = name;
      this.age = age;

   public Employee(int age)
      System.out.println("We are inside Employee(int age) constructor");
      this.age = age; 

   public String getName()
      return name;

   public void setName(String name)
   { = name;

   public int getAge()
      return age;

   public void setAge(int age)
      this.age = age;

In the above example you can see overloaded constructors. Name of the constructors is same but each constructors has different parameters.

Here are some resources which throw more light on constructor overloading in java,


Constructor explanation.

What Vim command(s) can be used to quote/unquote words?

Here's some mapping that could help:

:nnoremap <Leader>q" ciw""<Esc>P
:nnoremap <Leader>q' ciw''<Esc>P
:nnoremap <Leader>qd daW"=substitute(@@,"'\\\|\"","","g")<CR>P

If you haven't changed the mapleader variable, then activate the mapping with \q" \q' or \qd. They add double quote around the word under the cursor, single quote around the word under the cursor, delete any quotes around the word under the cursor respectively.

How to change maven java home

Great helps above, but if you having the similar environment like I did, this is how I get it to work.

  • having a few jdk running, openjdk, oracle jdk and a few versions.
  • install apache-maven via yum, package is apache-maven-3.2.1-1.el6.noarch

Edit this file /etc/profile.d/, such as the following, note that it will affect the whole system.

$ cat /etc/profile.d/
# change below to the jdk you want mvn to reference.
export M2_HOME
export PATH
export JAVA_HOME

Regex AND operator

Example of a Boolean (AND) plus Wildcard search, which I'm using inside a javascript Autocomplete plugin:

String to match: "my word"

String to search: "I'm searching for my funny words inside this text"

You need the following regex: /^(?=.*my)(?=.*word).*$/im


^ assert position at start of a line

?= Positive Lookahead

.* matches any character (except newline)

() Groups

$ assert position at end of a line

i modifier: insensitive. Case insensitive match (ignores case of [a-zA-Z])

m modifier: multi-line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)

Test the Regex here:

So, you can create a javascript function that:

  1. Replace regex reserved characters to avoid errors
  2. Split your string at spaces
  3. Encapsulate your words inside regex groups
  4. Create a regex pattern
  5. Execute the regex match


function fullTextCompare(myWords, toMatch){_x000D_
    //Replace regex reserved characters_x000D_
    myWords=myWords.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&');_x000D_
    //Split your string at spaces_x000D_
    arrWords = myWords.split(" ");_x000D_
    //Encapsulate your words inside regex groups_x000D_
    arrWords = n ) {_x000D_
        return ["(?=.*"+n+")"];_x000D_
    //Create a regex pattern_x000D_
    sRegex = new RegExp("^"+arrWords.join("")+".*$","im");_x000D_
    //Execute the regex match_x000D_
//Using it:_x000D_
    fullTextCompare("my word","I'm searching for my funny words inside this text")_x000D_
    fullTextCompare("y wo","I'm searching for my funny words inside this text")_x000D_

How to prevent IFRAME from redirecting top-level window

Try using the onbeforeunload property, which will let the user choose whether he wants to navigate away from the page.


In HTML5 you can use sandbox property. Please see Pankrat's answer below.

How to delete last character in a string in C#?

It's better if you use string.Join.

 class Product
   public int ProductID { get; set; }
 static void Main(string[] args)
   List<Product> products = new List<Product>()
         new Product { ProductID = 1 },
         new Product { ProductID = 2 },
         new Product { ProductID = 3 }
   string theURL = string.Join("&", products.Select(p => string.Format("productID={0}", p.ProductID)));

command/usr/bin/codesign failed with exit code 1- code sign error

I had the same error on January 2018 with xcode 8.2.1

Before I try to open xcode I couldn't because the system was updating. I tried sometime later and it let me working on it, and then I got the same error.

I followed most of the solutions described in this article but they didn't work for me.

Then I remembered the message about the system updating and I tried to reboot the machine.

And that did the magic. It worked for me.

pass JSON to HTTP POST Request

You don't want multipart, but a "plain" POST request (with Content-Type: application/json) instead. Here is all you need:

var request = require('request');

var requestData = {
  request: {
    slice: [
        origin: "ZRH",
        destination: "DUS",
        date: "2014-12-02"
    passengers: {
      adultCount: 1,
      infantInLapCount: 0,
      infantInSeatCount: 0,
      childCount: 0,
      seniorCount: 0
    solutions: 2,
    refundable: false

        { json: true, body: requestData },
        function(err, res, body) {
  // `body` is a js object if request was successful

header location not working in my php code

It took me some time to figure this out: My php-file was encoded in UTF-8. And the BOM prevented header location to work properly. In Notepad++ I set the file encoding to "UTF-8 without BOM" and the problem was gone.

How do you assert that a certain exception is thrown in JUnit 4 tests?

Just make a Matcher that can be turned off and on, like this:

public class ExceptionMatcher extends BaseMatcher<Throwable> {
    private boolean active = true;
    private Class<? extends Throwable> throwable;

    public ExceptionMatcher(Class<? extends Throwable> throwable) {
        this.throwable = throwable;

    public void on() { = true;

    public void off() { = false;

    public boolean matches(Object object) {
        return active && throwable.isAssignableFrom(object.getClass());

    public void describeTo(Description description) {
        description.appendText("not the covered exception type");

To use it:

add public ExpectedException exception = ExpectedException.none();, then:

ExceptionMatcher exMatch = new ExceptionMatcher(MyException.class);

How do I delete a Git branch locally and remotely?

Now you can do it with the GitHub Desktop application.

After launching the application

  1. Click on the project containing the branch
  2. Switch to the branch you would like to delete

    Switching branch

  3. From the "Branch" menu, select, "Unpublish...", to have the branch deleted from the GitHub servers.

    Unpublish branch

  4. From the "Branch" menu, select, 'Delete "branch_name"...', to have the branch deleted off of your local machine (AKA the machine you are currently working on)

    Delete local branch

Remove last character from C++ string

buf.erase(buf.size() - 1);

This assumes you know that the string is not empty. If so, you'll get an out_of_range exception.

How do you append rows to a table using jQuery?

The following code works

<script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript">
function AddRow()
    $('#myTable').append('<tr><td>test 2</td></tr>')
<input type="button" id="btnAdd" onclick="AddRow()"/>
<a href="">test</a>
<table id="myTable">
  <tbody >

Note this will work as of jQuery 1.4 even if the table includes a <tbody> element:

jQuery since version 1.4(?) automatically detects if the element you are trying to insert (using any of the append(), prepend(), before(), or after() methods) is a <tr> and inserts it into the first <tbody> in your table or wraps it into a new <tbody> if one doesn't exist.

How to declare 2D array in bash

For simulating a 2-dimensional array, I first load the first n-elements (the elements of the first column)

local pano_array=()  


for line in $(grep  "filename" "$file")
  url=$(extract_url_from_xml $line)

To add the second column, I define the size of the first column and calculate the values in an offset variable



while [[ $i -lt $array_len ]]
  found_file=$(get_file $url)


Returning from a void function

An old question, but I'll answer anyway. The answer to the actual question asked is that the bare return is redundant and should be left out.

Furthermore, the suggested value is false for the following reason:

if (ret<0) return;

Redefining a C reserved word as a macro is a bad idea on the face of it, but this particular suggestion is simply unsupportable, both as an argument and as code.

How do you run `apt-get` in a dockerfile behind a proxy?

Updated on 02/10/2018

With new feature in docker option --config, you needn't set Proxy in Dockerfile any more. You can have same Dockerfile to be used in and out corporate environment.

--config string      Location of client config files (default "~/.docker")

or environment variable DOCKER_CONFIG

`DOCKER_CONFIG` The location of your client configuration files.

$ export DOCKER_CONFIG=~/.docker

I recommend to set proxy with httpProxy, httpsProxy, ftpProxy and noProxy (The official document misses the variable ftpProxy which is useful sometimes)

     "httpProxy": "",
     "httpsProxy": "",
     "ftpProxy": "",
     "noProxy": "*,"

Adjust proxy IP and port if needed and save to ~/.docker/config.json

After yo set properly with it, you can run docker build and docker run as normal.

$ docker build -t demo . 

$ docker run -ti --rm demo env|grep -ri proxy
(standard input):http_proxy=
(standard input):HTTPS_PROXY=
(standard input):https_proxy=
(standard input):NO_PROXY=*,
(standard input):no_proxy=*,
(standard input):FTP_PROXY=
(standard input):ftp_proxy=
(standard input):HTTP_PROXY=

Old answer (Decommissioned)

Below setting in Dockerfile works for me. I tested in CoreOS, Vagrant and boot2docker. Suppose the proxy port is 3128

In Centos:

ENV http_proxy=ip:3128 
ENV https_proxy=ip:3128

In Ubuntu:

ENV http_proxy 'http://ip:3128'
ENV https_proxy 'http://ip:3128'

Be careful of the format, some have http in it, some haven't, some with single quota. if the IP address is, then the setting will be:

In Centos:

ENV http_proxy= 
ENV https_proxy=

In Ubuntu:

ENV http_proxy ''
ENV https_proxy ''

If you need set proxy in coreos, for example to pull the image

cat /etc/systemd/system/docker.service.d/http-proxy.conf


How to convert string to integer in PowerShell


2.032 MB (2,131,022 bytes)


$u=$u.trimend(" bytes)") #yields 2.032 MB (2,131,022

$u=$u.Split("(") #yields `$u[1]` as 2,131,022


The result is 2131022 in integer form.

typeof operator in C

Since typeof is a compiler extension, there is not really a definition for it, but in the tradition of C it would be an operator, e.g sizeof and _Alignof are also seen as an operators.

And you are mistaken, C has dynamic types that are only determined at run time: variable modified (VM) types.

size_t n = strtoull(argv[1], 0, 0);
double A[n][n];
typeof(A) B;

can only be determined at run time.

AngularJS : Custom filters and ng-repeat

You can call more of 1 function filters in the same ng-repeat filter

<article data-ng-repeat="result in results | filter:search() | filter:filterFn()" class="result">

How can I list all tags for a Docker image on a remote registry?

If folks want to read tags from the RedHat registry at then the steps are:

# example nodejs-12 image
# Get an oAuth token based on a service account username and password
TOKEN=$(curl --silent -u "$REGISTRY_USER":"$REGISTRY_PASSWORD" "" |  jq --raw-output '.token')
# Grab the tags
wget -q --header="Accept: application/json" --header="Authorization: Bearer $TOKEN" -O - "$REDHAT_REGISTRY_API/tags/list" | jq -r '."tags"[]' 

If you want to compare what you have in your local openshift registry against what is in the upstream then here is a complete script.

No suitable records were found verify your bundle identifier is correct

Double check the Bundle OS Type code in your App's info.plist, for me, the only way around this error was to set it to APPL.

The weird thing is that the error was regarding to my frameworks bundle id, tho changing the above in my app solved it.

Schedule automatic daily upload with FileZilla

FileZilla does not have any command line arguments (nor any other way) that allow an automatic transfer.

Some references:

Though you can use any other client that allows automation.

You have not specified, what protocol you are using. FTP or SFTP? You will definitely be able to use WinSCP, as it supports all protocols that FileZilla does (and more).

Combine WinSCP scripting capabilities with Windows Scheduler:

A typical WinSCP script for upload (with SFTP) looks like:

open sftp://user:[email protected]/ -hostkey="ssh-rsa 2048 xxxxxxxxxxx...="
put c:\mypdfs\*.pdf /home/user/

With FTP, just replace the sftp:// with the ftp:// and remove the -hostkey="..." switch.

Similarly for download: How to schedule an automatic FTP download on Windows?

WinSCP can even generate a script from an imported FileZilla session.

For details, see the guide to FileZilla automation.

(I'm the author of WinSCP)

Another option, if you are using SFTP, is the psftp.exe client from PuTTY suite.

Using sessions & session variables in a PHP Login Script


//extract data from submit post 

    if($user=="user" && $pass=="pass")    
        $_SESSION['user']= $user;       
        //if correct password and name store in session 
    } else {
        echo "Invalid user and password";

Converting a string to an integer on Android

See the Integer class and the static parseInt() method:


You will need to catch NumberFormatException though in case of problems whilst parsing, so:

int myNum = 0;

try {
    myNum = Integer.parseInt(et.getText().toString());
} catch(NumberFormatException nfe) {
   System.out.println("Could not parse " + nfe);
} Software caused connection abort: recv failed

This usually means that there was a network error, such as a TCP timeout. I would start by placing a sniffer (wireshark) on the connection to see if you can see any problems. If there is a TCP error, you should be able to see it. Also, you can check your router logs, if this is applicable. If wireless is involved anywhere, that is another source for these kind of errors.

Convert list of dictionaries to a pandas DataFrame

Supposing d is your list of dicts, simply:

df = pd.DataFrame(d)

Note: this does not work with nested data.

On delete cascade with doctrine2

There are two kinds of cascades in Doctrine:

1) ORM level - uses cascade={"remove"} in the association - this is a calculation that is done in the UnitOfWork and does not affect the database structure. When you remove an object, the UnitOfWork will iterate over all objects in the association and remove them.

2) Database level - uses onDelete="CASCADE" on the association's joinColumn - this will add On Delete Cascade to the foreign key column in the database:

@ORM\JoinColumn(name="father_id", referencedColumnName="id", onDelete="CASCADE")

I also want to point out that the way you have your cascade={"remove"} right now, if you delete a Child object, this cascade will remove the Parent object. Clearly not what you want.

How to sum data.frame column values?

to order after the colsum :


if more than 20+ columns

order(colSums(people[,c(5:25)],decreasing=TRUE) ##in case of keeping the first 4 columns remaining.

jQuery select change show/hide div event

I used the following jQuery-based snippet to have a select-element show a div-element that has an id that matches the value of the option-element while hiding the divs that do not match. Not sure that it's the best way, but it is a way.

    var myID = $(this).val();_x000D_
        myID === $(this).attr('id') ? $(this).show() : $(this).hide();_x000D_
.panel {display: none;}_x000D_
#one {display: block;}
<select id="sectionChooser">_x000D_
    <option value="one" selected>Thing One</option>_x000D_
    <option value="two">Thing Two</option>_x000D_
    <option value="three">Thing Three</option>_x000D_
<div class="panel" id="one">_x000D_
    <p>Thing One</p>_x000D_
<div class="panel" id="two">_x000D_
    <p>Thing Two</p>_x000D_
<div class="panel" id="three">_x000D_
    <p>Thing Three</p>_x000D_
<script src=""></script>

How can I use grep to find a word inside a folder?

Why not do a recursive search to find all instances in sub directories:

grep -r 'text' *

This works like a charm.

Get SSID when WIFI is connected

I listen for WifiManager.NETWORK_STATE_CHANGED_ACTION in a broadcast receiver

if (WifiManager.NETWORK_STATE_CHANGED_ACTION.equals (action)) {
        NetworkInfo netInfo = intent.getParcelableExtra (WifiManager.EXTRA_NETWORK_INFO);
        if (ConnectivityManager.TYPE_WIFI == netInfo.getType ()) {

I check for netInfo.isConnected (). Then I am able to use

WifiManager wifiManager = (WifiManager) getSystemService (Context.WIFI_SERVICE);
WifiInfo info = wifiManager.getConnectionInfo ();
String ssid  = info.getSSID();


From android 8.0 onwards we wont be getting SSID of the connected network unless GPS is turned on.

How do I concatenate two lists in Python?

You could use the append() method defined on list objects:

mergedlist =[]
for elem in listone:
for elem in listtwo:

Pandas: create two new columns in a dataframe with values calculated from a pre-existing column

I'd just use zip:

In [1]: from pandas import *

In [2]: def calculate(x):
   ...:     return x*2, x*3

In [3]: df = DataFrame({'a': [1,2,3], 'b': [2,3,4]})

In [4]: df
   a  b
0  1  2
1  2  3
2  3  4

In [5]: df["A1"], df["A2"] = zip(*df["a"].map(calculate))

In [6]: df
   a  b  A1  A2
0  1  2   2   3
1  2  3   4   6
2  3  4   6   9

Difference between Arrays.asList(array) and new ArrayList<Integer>(Arrays.asList(array))

package com.copy;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;

public class CopyArray {

    public static void main(String[] args) {
        List<Integer> list1, list2 = null;
        Integer[] intarr = { 3, 4, 2, 1 };
        list1 = new ArrayList<Integer>(Arrays.asList(intarr));
        list2 = Arrays.asList(intarr);
        // list2.add(40); Here, we can't modify the existing list,because it's a wrapper
        Iterator<Integer> itr1 = list1.iterator();
        while (itr1.hasNext()) {
        Iterator<Integer> itr2 = list2.iterator();
        while (itr2.hasNext()) {

Hive: Filtering Data between Specified Dates when Date is a String

You have to convert string formate to required date format as following and then you can get your required result.

hive> select * from salesdata01 where from_unixtime(unix_timestamp(Order_date, 'dd-MM-yyyy'),'yyyy-MM-dd') >= from_unixtime(unix_timestamp('2010-09-01', 'yyyy-MM-dd'),'yyyy-MM-dd') and from_unixtime(unix_timestamp(Order_date, 'dd-MM-yyyy'),'yyyy-MM-dd') <= from_unixtime(unix_timestamp('2011-09-01', 'yyyy-MM-dd'),'yyyy-MM-dd') limit 10;
1   3   13-10-2010  Low 6.0 261.54  0.04    Regular Air -213.25 38.94
80  483 10-07-2011  High    30.0    4965.7593   0.08    Regular Air 1198.97 195.99
97  613 17-06-2011  High    12.0    93.54   0.03    Regular Air -54.04  7.3
98  613 17-06-2011  High    22.0    905.08  0.09    Regular Air 127.7   42.76
103 643 24-03-2011  High    21.0    2781.82 0.07    Express Air -695.26 138.14
127 807 23-11-2010  Medium  45.0    196.85  0.01    Regular Air -166.85 4.28
128 807 23-11-2010  Medium  32.0    124.56  0.04    Regular Air -14.33  3.95
160 995 30-05-2011  Medium  46.0    1815.49 0.03    Regular Air 782.91  39.89
229 1539    09-03-2011  Low 33.0    511.83  0.1 Regular Air -172.88 15.99
230 1539    09-03-2011  Low 38.0    184.99  0.05    Regular Air -144.55 4.89
Time taken: 0.166 seconds, Fetched: 10 row(s)
hive> select * from salesdata01 where from_unixtime(unix_timestamp(Order_date, 'dd-MM-yyyy'),'yyyy-MM-dd') >= from_unixtime(unix_timestamp('2010-09-01', 'yyyy-MM-dd'),'yyyy-MM-dd') and from_unixtime(unix_timestamp(Order_date, 'dd-MM-yyyy'),'yyyy-MM-dd') <= from_unixtime(unix_timestamp('2010-12-01', 'yyyy-MM-dd'),'yyyy-MM-dd') limit 10;
1   3   13-10-2010  Low 6.0 261.54  0.04    Regular Air -213.25 38.94
127 807 23-11-2010  Medium  45.0    196.85  0.01    Regular Air -166.85 4.28
128 807 23-11-2010  Medium  32.0    124.56  0.04    Regular Air -14.33  3.95
256 1792    08-11-2010  Low 28.0    370.48  0.04    Regular Air -5.45   13.48
381 2631    23-09-2010  Low 27.0    1078.49 0.08    Regular Air 252.66  40.96
656 4612    19-09-2010  Medium  9.0 89.55   0.06    Regular Air -375.64 4.48
769 5506    07-11-2010  Critical    22.0    129.62  0.05    Regular Air 4.41    5.88
1457    10499   16-11-2010  Not Specified   29.0    6250.936    0.01    Delivery Truck  31.21   262.11
1654    11911   10-11-2010  Critical    25.0    397.84  0.0 Regular Air -14.75  15.22
2323    16741   30-09-2010  Medium  6.0 157.97  0.01    Regular Air -42.38  22.84
Time taken: 0.17 seconds, Fetched: 10 row(s)

Express.js req.body undefined

As already posted under one comment, I solved it using


instead of


I still don't know why the simple express.bodyParser() is not working...

Removing Data From ElasticSearch

You can delete the index by Kibana Console:

Console Icon

To get all index:

GET /_cat/indices?v

To delete a specific index:


How to reload page the page with pagination in Angular 2?

This should technically be achievable using window.location.reload():


<button (click)="refresh()">Refresh</button>


refresh(): void {


Here is a basic StackBlitz example showing the refresh in action. Notice the URL on "/hello" path is retained when window.location.reload() is executed.

Eclipse, regular expression search and replace

Using ...
search = (^.*import )(.*)(\(.*\):)
replace = $1$2

...replaces ...

from checks import checklist(_list):


from checks import checklist

Blocks in regex are delineated by parenthesis (which are not preceded by a "\")

(^.*import ) finds "from checks import " and loads it to $1 (eclipse starts counting at 1)

(.*) find the next "everything" until the next encountered "(" and loads it to $2. $2 stops at the "(" because of the next part (see next line below)

(\(.*\):) says "at the first encountered "(" after starting block $2...stop block $2 and start $3. $3 gets loaded with the "('any text'):" or, in the example, the "(_list):"

Then in the replace, just put the $1$2 to replace all three blocks with just the first two.


How do you easily create empty matrices javascript?

With ES6 spread operator: Array(9).fill([...Array(9)])

How to get MAC address of your machine using a C program?

  1. On Linux, use the service of "Network Manager" over the DBus.

  2. There is also good'ol shell program which can be invoke and the result grabbed (use an exec function under C):

$ /sbin/ifconfig | grep HWaddr

How to pass html string to webview on android

i have successfully done by below line

 //data == html data which you want to load
 String data = "Your data which you want to load";

 WebView webview = (WebView)this.findViewById(;
 webview.loadData(data, "text/html; charset=utf-8", "UTF-8");

Or You can try

 webview.loadDataWithBaseURL(null, data, "text/html", "utf-8", null);

Get the selected value in a dropdown using jQuery.

$('#availability').find('option:selected').val() // For Value 
$('#availability').find('option:selected').text() // For Text
$('#availability option:selected').val() // For Value 
$('#availability option:selected').text() // For Text

How to add extra whitespace in PHP?


echo "<p>hello\n";
echo "world</p>";

echo "\n\n";

echo "<p>\n\tindented\n</p>\n";

echo "
  easy formatting<br />
  across multiple lines!




  easy formatting<br /> 
  across multiple lines!

Is there a JavaScript strcmp()?

What about


How to shutdown my Jenkins safely?

Use http://[jenkins-server]/exit

This page shows how to use URL commands.

The system cannot find the file specified in java

I have copied your code and it runs fine.

I suspect you are simply having some problem in the actual file name of hello.txt, or you are running in a wrong directory. Consider verifying by the method suggested by @Eng.Fouad

Are there any Open Source alternatives to Crystal Reports?

Report Manager has been around for quite a few years. It's written in Delphi (at least it was originally) and has components that can be used in Delphi, but is usable via ActiveX or dll from just about any language. Now has a native .NET library too. Has a nifty report-serving webserver you can set up too. The designer gui looks and feels a little rough around the edges but it works.

Format y axis as percent

Based on the answer of @erwanp, you can use the formatted string literals of Python 3,

x = '2'
percentage = f'{x}%' # 2%

inside the FuncFormatter() and combined with a lambda expression.

All wrapped:

ax.yaxis.set_major_formatter(FuncFormatter(lambda y, _: f'{y}%'))

How to kill all processes with a given partial name?

Also you can use killall -r my_pattern. -r Interpret process name pattern as an extended regular expression.

killall -r my_pattern

How to send email in ASP.NET C#

    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Web;
    using System.Globalization;
    using System.Text.RegularExpressions;
    /// <summary>
    /// Summary description for RegexUtilities
    /// </summary>
    public class RegexUtilities
        bool InValid = false;
        public bool IsValidEmail(string strIn)
            InValid = false;
            if (String.IsNullOrEmpty(strIn))
                return false;
            // Use IdnMapping class to convert Unicode domain names.
            strIn = Regex.Replace(strIn, @"(@)(.+)$", this.DomainMapper);
            if (InValid)
                return false;
            // Return true if strIn is in valid e-mail format. 
            return Regex.IsMatch(strIn, @"^(?("")(""[^""]+?""@)|(([0-9a-z]((\.(?!\.))|[-!#\$%&'\*\+/=\?\^`\{\}\|~\w])*)(?<=[0-9a-z])@))" + @"(?(\[)(\[(\d{1,3}\.){3}\d{1,3}\])|(([0-9a-z][-\w]*[0-9a-z]*\.)+[a-z0-9]{2,17}))$",
        private string DomainMapper(Match match)
            // IdnMapping class with default property values.
            IdnMapping idn = new IdnMapping();
            string domainName = match.Groups[2].Value;
                domainName = idn.GetAscii(domainName);
            catch (ArgumentException)
                InValid = true;
            return match.Groups[1].Value + domainName;

 private void GetSendEmInfo()
        #region For Get All Type Email Informations..!!
        IPL.DoId = ddlName.SelectedValue;
        DataTable dt = IdBL.GetEmailS(IPL);
        if (dt.Rows.Count > 0)
            hid_MailId.Value = dt.Rows[0]["MailId"].ToString();
            hid_UsedPName.Value = dt.Rows[0]["UName"].ToString();
            hid_EmailSubject.Value = dt.Rows[0]["EmailSubject"].ToString();
            hid_EmailBody.Value = dt.Rows[0]["EmailBody"].ToString();
            hid_EmailIdName.Value = dt.Rows[0]["EmailIdName"].ToString();
            hid_EmPass.Value = dt.Rows[0]["EPass"].ToString();
            hid_SeName.Value = dt.Rows[0]["SenName"].ToString();
            hid_TNo.Value = dt.Rows[0]["TeNo"].ToString();
            hid_EmaLimit.Value = dt.Rows[0]["EmailLimit"].ToString();
            hidlink.Value = dt.Rows[0][link"].ToString();

        #region For Set Some Local Variables..!!
        int StartLmt, FinalLmt, SendCurrentMail;
        StartLmt = FinalLmt = SendCurrentMail = 0;
        bool Valid_LimitMail;
        Valid_LimitMail = true;
        /**For Get Finalize Limit For Send Mail**/
        FinalLmt = Convert.ToInt32(hid_EmailmaxLimit.Value);
        #region For Check Email Valid Limits..!!
        if (FinalLmt > 0)
            Valid_LimitMail = true;
            Valid_LimitMail = false;
        /**For Get Finalize Limit For Send Mail**/

        if (Valid_LimitMail == true)
            #region For Send Current Email Status..!!
            bool EmaiValid;
            string CreateFileName;
            string retmailflg = null;
            EmaiValid = false;

            #region For Set Start Limit And FinalLimit Send No Of Email..!!
            mPL.SendDate = DateTime.Now.ToString("dd-MMM-yyyy");
            DataTable dtsendEmail = m1BL.GetEmailSendLog(mPL);
            if (dtsendEmail.Rows.Count > 0)
                StartLmt = Convert.ToInt32(dtsendEmail.Rows[0]["SendNo_Of_Email"].ToString());
                StartLmt = 0;

            #region For Find Grid View Controls..!!
            for (int i = 0; i < GrdEm.Rows.Count; i++)
                #region For Find Grid view Controls..!!
                CheckBox Chk_SelectOne = (CheckBox)GrdEmp.Rows[i].FindControl("chkSingle");
                Label lbl_No = (Label)GrdEmAtt.Rows[i].FindControl("lblGrdCode");
                lblCode.Value = lbl_InNo.Text;

                Label lbl_EmailId = (Label)GrdEomAtt.Rows[i].FindControl("lblGrdEmpEmail");


                /**Region For If Check Box Checked Then**/
                if (Chk_SelectOne.Checked == true)
                    if (!string.IsNullOrEmpty(lbl_EmailId.Text))
                        #region For When Check Box Checked..!!
                        /**If Start Limit Less Or Equal To Then Condition Performs**/
                        if (StartLmt < FinalLmt)
                            StartLmt = StartLmt + 1;
                            Valid_LimitMail = false;
                            EmaiValid = false;
                        /**End Region**/
                        string[] SplitClients_Email = lbl_EmailId.Text.Split(',');
                        string Send_Email, Hold_Email;
                        Send_Email = Hold_Email = "";

                        int CountEmail;/**Region For Count Total Email**/
                        CountEmail = 0;/**First Time Email Counts Zero**/

                        Hold_Email = SplitClients_Email[0].ToString().Trim().TrimEnd().TrimStart().ToString();
                        /**Region For If Clients Have One Email**/
                        #region For First Emails Send On Client..!!
                        if (SplitClients_Email[0].ToString() != "")
                            if (EmailRegex.IsValidEmail(Hold_Email))
                                Send_Email = Hold_Email;
                                CountEmail = 1;
                                EmaiValid = true;
                                EmaiValid = false;
                        /**Region For If Clients Have One Email**/
                        /**Region For If Clients Have Two Email**/

                        /**Region For If Clients Have Two Email**/
                        if (EmaiValid == true)
                            #region For Create Email Body And Create File Name..!!
                            //fofile = Server.MapPath("PDFs");
                            fofile = Server.MapPath("~/vvv/vvvv/") + "/";
                            CreateFileName = lbl_INo.Text.ToString() + "_1" + ".Pdf";/**Create File Name**/
                            string[] orimail = Send_Email.Split(',');
                            string Billbody, TempInvoiceId;
                            // DateTime dtLstdate = new DateTime(Convert.ToInt32(txtYear.Text), Convert.ToInt32(ddlMonth.SelectedValue), 16);

                            //  DateTime IndtLmt = dtLstdate.AddMonths(1);
                            TempInvoiceId = "";

                            //byte[] Buffer = Encrypt.Encryptiondata(lbl_InvoiceNo.Text.ToString());
                            //TempInvoiceId = Convert.ToBase64String(Buffer);

                            #region Create Encrypted Path

                            byte[] EncCode = Encrypt.Encryptiondata(lbl_INo.Text);
                            hidEncrypteCode.Value = Convert.ToBase64String(EncECode);


                            //#region Create Email Body !!
                            //body = hid_EmailBody.Value.Replace("@greeting", lbl_CoName.Text).Replace("@free", hid_ToNo.Value).Replace("@llnk", "<a style='font-family: Tahoma; font-size: 10pt; color: #800000; font-weight: bold' href='http://1ccccc/ccc/ccc/ccc.aspx?EC=" + hidEncryptedCode.Value+ "' > C cccccccc </a>");

                            body = hid_EmailBody.Value.Replace("@greeting", "Hii").Replace("@No", hid_No.Value);/*For Mail*/

                            #region For Email Sender Informations..!!
                            for (int j = 0; j < CountEmail; j++)
                                //if (File.Exists(fofile + "\\" + CreateFileName))
                                lbl_EmailId.Text = orimail[j];
                                retmailflg = "";

                                /**Region For Send Email For Clients**/
                                //retmailflg = SendPreMail("Wp From " + lbl_CName.Text + "", body, lbl_EmailId.Text, lbl_IeNo.Text, hid_EmailIdName.Value, hid_EmailPassword.Value);
                                retmailflg = SendPreMail(hid_EmailSubject.Value, Body, lbl_EmailId.Text, lbl_No.Text, hid_EmailIdName.Value, hid_EmailPassword.Value);
                                /**End Region**/

                                /**Region For Create Send Email Log  When Email Send Successfully**/
                                if (retmailflg == "True")
                                    SendCurrentMail = Convert.ToInt32(SendCurrentMail) + 1;
                                    StartLmt = Convert.ToInt32(StartLmt) + 1;

                                    if (SendCurrentMail > 0)
                                        CreateEmailLog(lbl_InNo.Text, StartLmt, hid_EmailIdName.Value, lbl_EmailId.Text);

                                /**End Region**/
                /**End Region**/

    private void CreateEmailLog(string UniqueId, int StartLmt, string FromEmailId, string TotxtEmailId)
        FPL.EmailId_From = FromEmailId;
        FPL.To_EmailId = TotxtEmailId;
        FPL.SendDate = DateTime.Now.ToString("dd-MMM-yyyy");
        FPL.EmailUniqueId = UniqueId;
        FPL.SendNo_Of_Email = StartLmt.ToString();
        FPL.LoginUserId = Session["LoginUserId"].ToString();
        int i = FBL.InsertEmaDoc(FPL);

    public string SendPreMail(string emsub, string embody, string EmailId, string FileId, string EmailFromId, string Password)
        string retval = "False";
            string emailBody, emailSubject, emailToList, emailFrom,
            accountPassword, smtpServer;
            bool enableSSL;
            int port;

            emailBody = embody;
            emailSubject = emsub;
            emailToList = EmailId;
            emailFrom = EmailFromId;
            accountPassword = Password;
            smtpServer = "";
            enableSSL = true;
            port = 587;

            string crefilename;
            string fofile;
            fofile = Server.MapPath("PDF");
            crefilename = FileId + ".Pdf";

            string[] att = { crefilename };

            string retemail, insertqry;
            retemail = "";

            retemail = SendEmail(emailBody, emailSubject, emailFrom, emailToList, att, smtpServer, enableSSL, accountPassword, port);

            if (retemail == "True")

                retval = retemail;
            retval = "False";

        return retval;

    public string SendEmail(string emailBody, string emailSubject, string emailFrom, string emailToList, string[] attachedFiles, string smtpIPAddress, bool enableSSL, string accountPassword, int port)
        MailMessage mail = new MailMessage();
        string retflg;
        retflg = "False";
            mail.From = new MailAddress(emailFrom);
            if (emailToList.Contains(";"))
                emailToList = emailToList.Replace(";", ",");

            mail.Subject = emailSubject;
            mail.IsBodyHtml = true;
            mail.Body = emailBody;

            SmtpClient smtp = new SmtpClient();
            smtp.Host = "";
            smtp.EnableSsl = true;
            NetworkCredential NetworkCred = new NetworkCredential(emailFrom, accountPassword);
            smtp.UseDefaultCredentials = true;
            smtp.Credentials = NetworkCred;
            smtp.Port = 587;
            retflg = "True";

            retflg = "False";
        return retflg;

ActionBarActivity: cannot be resolved to a type

Add this line to dependencies in build.gradle:

dependencies {
compile ''


Errors in pom.xml with dependencies (Missing artifact...)

It means maven is not able to download artifacts from repository. Following steps will help you:

  1. Go to repository browser and check if artifact exist.
  2. Check settings.xml to see if proper respository is specified.
  3. Check proxy settings.

How to set default values in Rails?

Generate a migration and use change_column_default, is succinct and reversible:

class SetDefaultAgeInPeople < ActiveRecord::Migration[5.2]
  def change
    change_column_default :people, :age, { from: nil, to: 0 }

Usages of doThrow() doAnswer() doNothing() and doReturn() in mockito

To add a bit to accepted answer ...

If you get an UnfinishedStubbingException, be sure to set the method to be stubbed after the when closure, which is different than when you write Mockito.when

Mockito.doNothing().when(mock).method()    //method is declared after 'when' closes

Mockito.when(mock.method()).thenReturn(something)   //method is declared inside 'when'

How to check if a function exists on a SQL database

I've found you can use a very non verbose and straightforward approach to checking for the existence various SQL Server objects this way:

IF OBJECTPROPERTY (object_id('schemaname.scalarfuncname'), 'IsScalarFunction') = 1
IF OBJECTPROPERTY (object_id('schemaname.tablefuncname'), 'IsTableFunction') = 1
IF OBJECTPROPERTY (object_id('schemaname.procname'), 'IsProcedure') = 1

This is based on the OBJECTPROPERTY function which is available in SQL 2005+. The MSDN article can be found here.

The OBJECTPROPERTY function uses the following signature:

OBJECTPROPERTY ( id , property ) 

You pass a literal value into the property parameter, designating the type of object you are looking for. There's a massive list of values you can supply.

how to create insert new nodes in JsonNode?

These methods are in ObjectNode: the division is such that most read operations are included in JsonNode, but mutations in ObjectNode and ArrayNode.

Note that you can just change first line to be:

ObjectNode jNode = mapper.createObjectNode();
// version ObjectMapper has should return ObjectNode type


ObjectNode jNode = (ObjectNode) objectCodec.createObjectNode();
// ObjectCodec is in core part, must be of type JsonNode so need cast

Calling UserForm_Initialize() in a Module

From a module:


Just make sure that in your userform, you update the sub like so:

Public Sub UserForm_Initialize() so it can be called from outside the form.

Alternately, if the Userform hasn't been loaded:

UserFormName.Show will end up calling UserForm_Initialize because it loads the form.

How to open a different activity on recyclerView item onclick

iconView = (ImageView) itemLayoutView .findViewById(;

        itemLayoutView.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {

                Intent intent = new Intent(v.getContext(), SecondPage.class);
                Toast.makeText(v.getContext(), "os version is: " + feed.getTitle(), Toast.LENGTH_SHORT).show();

How to disable manual input for JQuery UI Datepicker field?

I think you should add style="background:white;" to make looks like it is writable

<input type="text" size="23" name="dateMonthly" id="dateMonthly" readonly="readonly"   style="background:white;"/>

Circular gradient in android

Here is the complete xml with gradient, stoke & circular shape.

<?xml version="1.0" encoding="utf-8"?>

    android:shape="oval" >

    <!-- You can use gradient with below attributes-->
        android:type="linear" />

    <!-- You can omit below tag if you don't need stroke -->
   <stroke android:color="#3b91d7" android:width="5dp"/>

    <!-- Set the same value for both width and height to get a circular shape -->
    <size android:width="200dp" android:height="200dp"/>

    <!--if you need only a single color filled shape-->
    <solid android:color="#e42828"/>


how to use font awesome in own css?

Try this way. In your css file change font-family: FontAwesome into font-family: "FontAwesome"; or font-family: 'FontAwesome';. I've solved the same problem using this method.

Stop node.js program from command line

$ sudo killall node in another terminal works on mac, while killall node not working:

$ killall node
No matching processes belonging to you were found

Change Activity's theme programmatically

I have used this code to implement dark worked fine for me...You can use it in a switch on....listener...

//setting up Night Mode...
//Store current mode in a sharedprefernce to retrieve on restarting app
            editor.putBoolean("NightMode", true);
//restart all the activities to apply changed mode...
                    .addNextIntent(new Intent(getActivity(), MainActivity.class))

How to read a string one letter at a time in python

Use 'index'.

def GetMorseCode(letter):
   index = letterList.index(letter)
   code = codeList[index]
   return code

Of course, you'll want to validate your input letter (convert its case as necessary, make sure it's in the list in the first place by checking that index != -1), but that should get you down the path.

Vibrate and Sound defaults on notification

To support SDK version >= 26, you also should build NotificationChanel and set a vibration pattern and sound there. There is a Kotlin code sample:

    val vibrationPattern = longArrayOf(500)
    val soundUri = "<your sound uri>"

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            val notificationManager =    
                 getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
            val attr = AudioAttributes.Builder()
            val channelName: CharSequence = Constants.NOTIFICATION_CHANNEL_NAME
            val importance = NotificationManager.IMPORTANCE_HIGH
            val notificationChannel =
                NotificationChannel(Constants.NOTIFICATION_CHANNEL_ID, channelName, importance)
                notificationChannel.lightColor = Color.RED
                notificationChannel.setSound(soundUri, attr)
                notificationChannel.vibrationPattern = vibrationPattern

And this is the builder:

 with(NotificationCompat.Builder(applicationContext, Constants.NOTIFICATION_CHANNEL_ID)) {
        setContentTitle("Some title")
        setContentText("Some content")
            // this is an extension function of context you should build
            // your own pending intent and place it here
                Intent(applicationContext, target).apply {
                    flags = Intent.FLAG_ACTIVITY_NEW_TASK or Intent.FLAG_ACTIVITY_CLEAR_TASK

        return build()

Be sure your AudioAttributes are chosen right to read more here.

How to Run a jQuery or JavaScript Before Page Start to Load

      window.location = "";

This will force the checking of condition and the change in url location before the page renders anything. It is worth noting that you will specifically want to do this before the call to the jQuery library so you can avoid all that library loading. Some might also argue that this would be better placed in a wrapper method and called so here is that method:

function redirectHandler(condition, url){
    window.location = url;
    return false;

That would allow you to check multiple conditions and redirect to different locations based on it:

if(redirectHandler(nologgedin, "/login.php")||redirectHandler(adminuser, "/admin.php"));

or if you only need it to run once and only once, but you like having nothing in the global namespace:

(function(condition, url){
})(!loggedin, "/login.asp");

How to check 'undefined' value in jQuery

I know I am late to answer the function but jquery have a in build function to do this

if(jQuery.type(val) === "undefined"){
    //Some code goes here

Refer jquery API document of jquery.type for the same.

fix Read timed out

Here are few pointers/suggestions for investigation

  1. I see that every time you vote, you call vote method which creates a fresh HTTP connection.
  2. This might be a problem. I would suggest to use a single HttpClient instance to post to the server. This way it wont create too many connections from the client side.
  3. At the end of everything, HttpClient needs to be shut and hence call httpclient.getConnectionManager().shutdown(); to release the resources used by the connections.

How to get main div container to align to centre?

Do not use the * selector as that will apply to all elements on the page. Suppose you have a structure like this:

    <div id="content">
        <b>This is the main container.</b>

You can then center the #content div using:

#content {
    width: 400px;
    margin: 0 auto;
    background-color: #66ffff;

Don't know what you've seen elsewhere but this is the way to go. The * { margin: 0; padding: 0; } snippet you've seen is for resetting browser's default definitions for all browsers to make your site behave similarly on all browsers, this has nothing to do with centering the main container.

Most browsers apply a default margin and padding to some elements which usually isn't consistent with other browsers' implementations. This is why it is often considered smart to use this kind of 'resetting'. The reset snippet you presented is the most simplest of reset stylesheets, you can read more about the subject here:

Shell script to set environment variables

You need to run the script as source or the shorthand .

source ./


. ./

This will run within the existing shell, ensuring any variables created or modified by the script will be available after the script completes.

Running the script just using the filename will execute the script in a separate subshell.

Refresh a page using PHP

You cannot do it in PHP. Once the page is loaded, PHP dies and is out of control.

You have a few options:

  • Use JavaScript
  • Use the refresh meta tag, <meta http-equiv="refresh" content="5">

I think that the refresh meta tag is the easiest and most convenient.

How do I execute a bash script in Terminal?

Firstly you have to make it executable using: chmod +x name_of_your_file_script.

After you made it executable, you can run it using ./same_name_of_your_file_script

functional way to iterate over range (ES6/7)

ES7 Proposal

Warning: Unfortunately I believe most popular platforms have dropped support for comprehensions. See below for the well-supported ES6 method

You can always use something like:

[for (i of Array(7).keys()) i*i];

Running this code on Firefox:

[ 0, 1, 4, 9, 16, 25, 36 ]

This works on Firefox (it was a proposed ES7 feature), but it has been dropped from the spec. IIRC, Babel 5 with "experimental" enabled supports this.

This is your best bet as array-comprehension are used for just this purpose. You can even write a range function to go along with this:

var range = (u, l = 0) => [ for( i of Array(u - l).keys() ) i + l ]

Then you can do:

[for (i of range(5)) i*i] // 0, 1, 4, 9, 16, 25
[for (i of range(5,3)) i*i] // 9, 16, 25


A nice way to do this any of:

[...Array(7).keys()].map(i => i * i);
Array(7).fill().map((_,i) => i*i);
[...Array(7)].map((_,i) => i*i);

This will output:

[ 0, 1, 4, 9, 16, 25, 36 ]

string sanitizer for filename

$fname = str_replace('/','',$fname);

Since users might use the slash to separate two words it would be better to replace with a dash instead of NULL

npx command not found

Remove NodeJs and npm in your system and reinstall it by following commands


sudo apt remove nodejs
sudo apt remove npm

Fresh Installation

sudo apt install nodejs
sudo apt install npm

Configuration optional, in some cases users may face permission errors.

  1. user defined directory where npm will install packages

    mkdir ~/.npm-global

  2. configure npm

    npm config set prefix '~/.npm-global'

  3. add directory to path

    echo 'export PATH=~/.npm-global/bin:$PATH' >> ~/.profile

  4. refresh path for the current session

    source ~/.profile

  5. cross-check npm and node modules installed successfully in our system

    node -v
    npm -v

Installation of npx

sudo npm i -g npx
npx -v

Well-done we are ready to go... now you can easily use npx anywhere in your system.

How do I pass multiple parameters in Objective-C?

The text before each parameter is part of the method name. From your example, the name of the method is actually


Each : represents an argument. In a method call, the method name is split at the :s and arguments appear after the :s. e.g.

[getBusStops: arg1 forTime: arg2]

Failed to configure a DataSource: 'url' attribute is not specified and no embedded datasource could be configured

I had the same issue resolved by add <scope>provided</scope>



What should I use to open a url instead of urlopen in urllib3

In urlip3 there's no .urlopen, instead try this:

import requests
html = requests.get(url)

How to Remove Line Break in String

just this:

str = Replace(str, vbCrLf, "")

Change values of select box of "show 10 entries" of jquery datatable

you can achieve this easily without writing Js. Just add an attribute called data-page-length={put your number here}. see example below, I used 100 for example

<table id="datatable-keytable" data-page-length='100' class="p-table table table-bordered" width="100%">

How to reload the current state?

Not sure why none of these seemed to work for me; the one that finally did it was:


This was with Angular 1.4.0

How do I tell Gradle to use specific JDK version?

If you have this problem from Intellij, try this options

  1. Set Gradle JVM Home enter image description here

  2. Set the JDK version in the Project module settings enter image description here

Bootstrap Collapse not Collapsing

You need jQuery see bootstrap's basic template

How to update a value, given a key in a hashmap?

Does the hash exist (with 0 as the value) or is it "put" to the map on the first increment? If it is "put" on the first increment, the code should look like:

if (hashmap.containsKey(key)) {
    hashmap.put(key, hashmap.get(key)+1);
} else { 

`require': no such file to load -- mkmf (LoadError)

I think is a little late but

sudo yum install -y gcc ruby-devel libxml2 libxml2-devel libxslt libxslt-devel

worked for me on fedora.

Write to custom log file from a Bash script

I did it by using a filter. Most linux systems use rsyslog these days. The config files are located at /etc/rsyslog.conf and /etc/rsyslog.d.

Whenever I run the command logger -t SRI some message, I want "some message" to only show up in /var/log/sri.log.

To do this I added the file /etc/rsyslog.d/00-sri.conf with the following content.

# Filter all messages whose tag starts with SRI
# Note that 'isequal, "SRI:"' or 'isequal "SRI"' will not work.
:syslogtag, startswith, "SRI" /var/log/sri.log

# The stop command prevents this message from getting processed any further.
# Thus the message will not show up in /var/log/messages.
& stop

Then restart the rsyslogd service:

systemctl restart rsyslog.service

Here is a shell session showing the results:

[root@rpm-server html]# logger -t SRI Hello World!
[root@rpm-server html]# cat /var/log/sri.log
Jun  5 10:33:01 rpm-server SRI[11785]: Hello World!
[root@rpm-server html]#
[root@rpm-server html]# # see that nothing shows up in /var/log/messages
[root@rpm-server html]# tail -10 /var/log/messages | grep SRI
[root@rpm-server html]#

isset in jQuery?

You can use length:

if($("#one").length) { // 0 == false; >0 == true

How can I convert a string to an int in Python?

def addition(a, b): return a + b

def subtraction(a, b): return a - b

def multiplication(a, b): return a * b

def division(a, b): return a / b

keepProgramRunning = True

print "Welcome to the Calculator!"

while keepProgramRunning:
 print "Please choose what you'd like to do:"

Loading existing .html file with android WebView

If your structure should be like this:




Then just do ( Android WebView: handling orientation changes )

    if(WebViewStateHolder.INSTANCE.getBundle() == null) { //this works only on single instance of webview, use a map with TAG if you need more
    } else {

Make sure you add

    WebSettings webSettings = webView.getSettings();
    if(android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.JELLY_BEAN) {

Then just use urls

    <meta charset="utf-8">
    <script src="../scripts/index.js"></script>
    <link rel="stylesheet" type="text/css" href="../css/index.css">

What's is the difference between include and extend in use case diagram?

This is great resource with great explanation: What is include at use case? What is Extend at use case?

Extending use case typically defines optional behavior. It is independent of the extending use case

Include used to extract common parts of the behaviors of two or more use cases

Show constraints on tables command

I use


This shows you the SQL statement necessary to receate mytable in its current form. You can see all the columns and their types (like DESC) but it also shows you constraint information (and table type, charset, etc.).

How can I determine browser window size on server side C#

Here how I solved it using Cookies:

First of all, inside the website main script:

var browserWindowSize = getCookie("_browserWindowSize");
var newSize = $(window).width() + "," + $(window).height();
var reloadForCookieRefresh = false;

if (browserWindowSize == undefined || browserWindowSize == null || newSize != browserWindowSize) {
    setCookie("_browserWindowSize", newSize, 30);
    reloadForCookieRefresh = true;

if (reloadForCookieRefresh)

function setCookie(name, value, days) {
    var expires = "";
    if (days) {
        var date = new Date();
        date.setTime(date.getTime() + (days * 24 * 60 * 60 * 1000));
        expires = "; expires=" + date.toUTCString();
    document.cookie = name + "=" + (value || "") + expires + "; path=/";

function getCookie(name) {
    var nameEQ = name + "=";
    var ca = document.cookie.split(';');
    for (var i = 0; i < ca.length; i++) {
        var c = ca[i];
        while (c.charAt(0) == ' ') c = c.substring(1, c.length);
        if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length, c.length);
    return null;

And inside MVC action filter:

public class SetCurrentRequestDataFilter : ActionFilterAttribute
    public override void OnActionExecuting(ActionExecutingContext filterContext)
        // currentRequestService is registered per web request using IoC
        var currentRequestService = iocResolver.Resolve<ICurrentRequestService>();

        if (filterContext.HttpContext.Request.Cookies.AllKeys.Contains("_browserWindowSize"))
            var browserWindowSize = filterContext.HttpContext.Request.Cookies.Get("_browserWindowSize").Value.Split(',');
            currentRequestService.browserWindowWidth = int.Parse(browserWindowSize[0]);
            currentRequestService.browserWindowHeight = int.Parse(browserWindowSize[1]);


Keep a line of text as a single line - wrap the whole line or none at all

You can use white-space: nowrap; to define this behaviour:

// HTML:

.nowrap {_x000D_
  white-space: nowrap ;_x000D_
      <span class="nowrap">How do I wrap this line of text</span>_x000D_
      <span class="nowrap">- asked by Peter 2 days ago</span>_x000D_

// CSS:
.nowrap {
  white-space: nowrap ;

How do I jump out of a foreach loop in C#?

It's not a direct answer to your question but there is a much easier way to do what you want. If you are using .NET 3.5 or later, at least. It is called Enumerable.Contains

bool found = sList.Contains("ok");

Managing jQuery plugin dependency in webpack

Add this to your plugins array in webpack.config.js

new webpack.ProvidePlugin({
    'window.jQuery': 'jquery',
    'window.$': 'jquery',

then require jquery normally


If pain persists getting other scripts to see it, try explicitly placing it in the global context via (in the entry js)

window.$ = jQuery;

CMake unable to determine linker language with C++

Confusing as it might be, the error also happens when a cpp file included in the project does not exist.

If you list your source files in CMakeLists.txt and mistakenly type a file name then you get this error.

Float sum with javascript

(parseFloat('2.3') + parseFloat('2.4')).toFixed(1);

its going to give you solution i suppose

How to increment variable under DOS?

Coming to the party very very late, but from my old memory of DOS batch files, you can keep adding a character to the string each loop then look for a string of that many of that character. for 250 iterations, you either have a very long "cycles" string, or you have one loop inside using one set of variables counting to 10, then another loop outside that uses another set of variable counting to 25.

Here is the basic loop to 30:

@echo off
rem put how many dots you want to loop
set cycles=..............................
set cntr=
set cntr=%cntr%.
echo around we go again
if "%cycles%"=="%cntr%" goto done
goto loop
echo around we went

Find unused code

ReSharper does a great job of finding unused code.

In the VS IDE, you can right click on the definition and choose 'Find All References', although this only works at the solution level.

Import-CSV and Foreach

You can create the headers on the fly (no need to specify delimiter when the delimiter is a comma):

Import-CSV $filepath -Header IP1,IP2,IP3,IP4 | Foreach-Object{
   Write-Host $_.IP1
   Write-Host $_.IP2

How to create a zip archive of a directory in Python?

You probably want to look at the zipfile module; there's documentation at

You may also want os.walk() to index the directory structure.

regex.test V.S. string.match to know if a string matches a regular expression

This is my benchmark results benchmark results

test 4,267,740 ops/sec ±1.32% (60 runs sampled)

exec 3,649,719 ops/sec ±2.51% (60 runs sampled)

match 3,623,125 ops/sec ±1.85% (62 runs sampled)

indexOf 6,230,325 ops/sec ±0.95% (62 runs sampled)

test method is faster than the match method, but the fastest method is the indexOf

How to avoid "cannot load such file -- utils/popen" from homebrew on OSX

After updating to El Capitan, /usr/local has root:wheel rights.

Change the rights back to the user using:

sudo chown -R $(whoami):admin /usr/local


brew doctor && brew update

This helped me to get Homebrew working again.

tr:hover not working

Try it:

css code:

.list1 tr:hover td {

The import cannot be resolved

Above solutions should solve your problem. If these do not, make sure you update your Android sdk using SDK manager and install the latest lib project and then repeat the above steps again.

HTML <select> selected option background-color CSS style

I realise this is an old post, but in case it helps, you can apply this CSS to have IE11 draw a dotted outline for the focus indication of a <select> element so that it resembles Firefox's focus indication: select:focus::-ms-value { background: transparent; color: inherit; outline-style: dotted; outline-width: thin; }

how to add or embed CKEditor in php page

After reading the Quick Start Guide

In your HTML page add an element that CKEditor should replace:

<textarea name="content" id="editor"></textarea>

Load the classic editor build (here CDN location is used):

<script src=""></script>

Call the ClassicEditor.create() method.

        .create( document.querySelector( '#editor' ) )
        .catch( error => {
            console.error( error );
        } );


<!DOCTYPE html>
    <meta charset="utf-8">
    <title>CKEditor 5 - Classic editor</title>
    <script src=""></script>
    <h1>Classic editor</h1>
    <textarea name="content" id="editor">
        <p>This is some sample content.</p>
            .create( document.querySelector( '#editor' ) )
            .catch( error => {
                console.error( error );
            } );

This example is for the specific classic editor. FOr other variants, only CDN will change.

RAW POST using cURL in PHP

Implementation with Guzzle library:

use GuzzleHttp\Client;
use GuzzleHttp\RequestOptions;

$httpClient = new Client();

$response = $httpClient->post(
        RequestOptions::BODY => 'POST raw request content',
        RequestOptions::HEADERS => [
            'Content-Type' => 'application/x-www-form-urlencoded',


PHP CURL extension:

$curlHandler = curl_init();

curl_setopt_array($curlHandler, [
    CURLOPT_URL => '',

     * Specify POST method
    CURLOPT_POST => true,

     * Specify request content
    CURLOPT_POSTFIELDS => 'POST raw request content',

$response = curl_exec($curlHandler);



Source code

How to find locked rows in Oracle

The below PL/SQL block finds all locked rows in a table. The other answers only find the blocking session, finding the actual locked rows requires reading and testing each row.

(However, you probably do not need to run this code. If you're having a locking problem, it's usually easier to find the culprit using GV$SESSION.BLOCKING_SESSION and other related data dictionary views. Please try another approach before you run this abysmally slow code.)

First, let's create a sample table and some data. Run this in session #1.

--Sample schema.
create table test_locking(a number);
insert into test_locking values(1);
insert into test_locking values(2);
update test_locking set a = a+1 where a = 1;

In session #2, create a table to hold the locked ROWIDs.

--Create table to hold locked ROWIDs.
create table locked_rowids(the_rowid rowid);
--Remove old rows if table is already created:
--delete from locked_rowids;

In session #2, run this PL/SQL block to read the entire table, probe each row, and store the locked ROWIDs. Be warned, this may be ridiculously slow. In your real version of this query, change both references to TEST_LOCKING to your own table.

--Save all locked ROWIDs from a table.
--WARNING: This PL/SQL block will be slow and will temporarily lock rows.
--You probably don't need this information - it's usually good enough to know
--what other sessions are locking a statement, which you can find in
    v_resource_busy exception;
    pragma exception_init(v_resource_busy, -00054);
    v_throwaway number;
    type rowid_nt is table of rowid;
    v_rowids rowid_nt := rowid_nt();
    --Loop through all the rows in the table.
    for all_rows in
        select rowid
        from test_locking
    ) loop
        --Try to look each row.
            select 1
            into v_throwaway
            from test_locking
            where rowid = all_rows.rowid
            for update nowait;
        --If it doesn't lock, then record the ROWID.
        exception when v_resource_busy then
            v_rowids(v_rowids.count) := all_rows.rowid;

    end loop;

    --Display count:
    dbms_output.put_line('Rows locked: '||v_rowids.count);

    --Save all the ROWIDs.
    --(Row-by-row because ROWID type is weird and doesn't work in types.)
    for i in 1 .. v_rowids.count loop
        insert into locked_rowids values(v_rowids(i));
    end loop;

Finally, we can view the locked rows by joining to the LOCKED_ROWIDS table.

--Display locked rows.
select *
from test_locking
where rowid in (select the_rowid from locked_rowids);


how to read certain columns from Excel using Pandas - Python

parse_cols is deprecated, use usecols instead

that is:

df = pd.read_excel(file_loc, index_col=None, na_values=['NA'], usecols = "A,C:AA")

CSS position:fixed inside a positioned element

Seems, css transforms can be used

"‘transform’ property establishes a new local coordinate system at the element",

but ... this is not cross-browser, seems only Opera works correctly

Interview question: Check if one string is a rotation of other string

Another Ruby solution based on the answer:

def rotation?(a, b); a.size == b.size and (b*2)[a]; end

Adding List<t>.add() another list

List<T>.Add adds a single element. Instead, use List<T>.AddRange to add multiple values.

Additionally, List<T>.AddRange takes an IEnumerable<T>, so you don't need to convert tripDetails into a List<TripDetails>, you can pass it directly, e.g.:


Alarm Manager Example

This code will help you to make a repeating alarm. The repeating time can set by you.


<?xml version="1.0" encoding="utf-8"?>
     <LinearLayout xmlns:android=""

    android:gravity="center" >

    android:singleLine="true" >

        <requestFocus />


    android:singleLine="true" />


    android:singleLine="true" />



        android:text="Set Alarm" />



public class MainActivity extends Activity {
    int hr = 0;
    int min = 0;
    int sec = 0;
    int result = 1;

    AlarmManager alarmManager;
    PendingIntent pendingIntent;
    BroadcastReceiver mReceiver;

    EditText ethr;
    EditText etmin;
    EditText etsec;

    protected void onCreate(Bundle savedInstanceState) {
        ethr = (EditText) findViewById(;
        etmin = (EditText) findViewById(;
        etsec = (EditText) findViewById(;

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

    protected void onDestroy() {

    public void onClickSetAlarm(View v) {
        String shr = ethr.getText().toString();
        String smin = etmin.getText().toString();
        String ssec = etsec.getText().toString();

            hr = 0;
        else {
            hr = Integer.parseInt(ethr.getText().toString());

            min = 0;
        else {
            min = Integer.parseInt(etmin.getText().toString());
            min = min*60*1000;

            sec = 0;
        else {
             sec = Integer.parseInt(etsec.getText().toString());
             sec = sec * 1000;
        result = hr+min+sec;
        alarmManager.setRepeating(AlarmManager.RTC_WAKEUP, System.currentTimeMillis(), result , pendingIntent); 

    private void RegisterAlarmBroadcast() {
        mReceiver = new BroadcastReceiver() {
            // private static final String TAG = "Alarm Example Receiver";
            public void onReceive(Context context, Intent intent) {
                Toast.makeText(context, "Alarm time has been reached", Toast.LENGTH_LONG).show();

        registerReceiver(mReceiver, new IntentFilter("sample"));
        pendingIntent = PendingIntent.getBroadcast(this, 0, new Intent("sample"), 0);
        alarmManager = (AlarmManager)(this.getSystemService(Context.ALARM_SERVICE));

    private void UnregisterAlarmBroadcast() {

If you need alarm only for a single time then replace

alarmManager.setRepeating(AlarmManager.RTC_WAKEUP, System.currentTimeMillis(), result , pendingIntent);


 alarmManager.set( AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + result , pendingIntent );

C# "internal" access modifier when doing unit testing

Keep using private by default. If a member shouldn't be exposed beyond that type, it shouldn't be exposed beyond that type, even to within the same project. This keeps things safer and tidier - when you're using the object, it's clearer which methods you're meant to be able to use.

Having said that, I think it's reasonable to make naturally-private methods internal for test purposes sometimes. I prefer that to using reflection, which is refactoring-unfriendly.

One thing to consider might be a "ForTest" suffix:

internal void DoThisForTest(string name)

private void DoThis(string name)
    // Real implementation

Then when you're using the class within the same project, it's obvious (now and in the future) that you shouldn't really be using this method - it's only there for test purposes. This is a bit hacky, and not something I do myself, but it's at least worth consideration.

Calculate mean across dimension in a 2D array

Here is a non-numpy solution:

>>> a = [[40, 10], [50, 11]]
>>> [float(sum(l))/len(l) for l in zip(*a)]
[45.0, 10.5]

Get docker container id from container name

I tried sudo docker container stats, and it will give out Container ID along with details of memory usage and Name, etc. If you want to stop viewing the process, do Ctrl+C. I hope you find it useful.

Java division by zero doesnt throw an ArithmeticException - why?

IEEE 754 defines 1.0 / 0.0 as Infinity and -1.0 / 0.0 as -Infinity and 0.0 / 0.0 as NaN.

By the way, floating point values also have -0.0 and so 1.0/ -0.0 is -Infinity.

Integer arithmetic doesn't have any of these values and throws an Exception instead.

To check for all possible values (e.g. NaN, 0.0, -0.0) which could produce a non finite number you can do the following.

if (Math.abs(tab[i] = 1 / tab[i]) < Double.POSITIVE_INFINITY)
   throw new ArithmeticException("Not finite");

Reset push notification settings for app

In addition to the answer of ianolito.

Had the same issue with an app I downloaded a year ago and denying push notification initially. Now wanting push notifications back, these steps worked for me on iOS 7 beta. Not sure which point(s) triggered it exactly.

  • Close and delete the app.
  • Go to your iCloud settings and delete the app from the iCloud. Do this on all other devices where you have iCloud backup for apps enabled. After deactivating and deleting make a fresh backup. The app should not be listed any more under the backups. (This is maybe why the Technical Note from Apple described by ianolito stopped working in iOS 5, since iCloud was introduced in iOS 5 and many have iCloud backup for apps enabled.)
  • Go to your time settings and set the time more than 1 month ahead.
  • Switch the iPhone off (no reset).
  • Wait a minute, switch it on again and download the app again.
  • Start the app and I was presented the dialog again.
  • Enable app backup again, since it is still deactivated. Correct the time.

Thank god I did not have to "Erase All Content And Settings". Maybe it will help someone.

Angular.js directive dynamic templateURL

emanuel.directive('hymn', function() {
   return {
       restrict: 'E',
       link: function(scope, element, attrs) {
           // some ode
       templateUrl: function(elem,attrs) {
           return attrs.templateUrl || 'some/path/default.html'

So you can provide templateUrl via markup

<hymn template-url="contentUrl"><hymn>

Now you just take a care that property contentUrl populates with dynamically generated path.

Submitting a multidimensional array via POST with php

you could submit all parameters with such naming:


then later you do something like this:

foreach ($_REQUEST['params'] as $item) {
    echo $item['topdiameter'];
    echo $item['bottomdiameter'];

CSS: how to add white space before element's content?

/* Most Accurate Setting if you only want
   to do this with CSS Pseudo Element */
p:before { 
   content: "\00a0";
   padding-right: 5px; /* If you need more space b/w contents */

Difference between HashSet and HashMap?

It's really a shame that both their names start with Hash. That's the least important part of them. The important parts come after the Hash - the Set and Map, as others have pointed out. What they are, respectively, are a Set - an unordered collection - and a Map - a collection with keyed access. They happen to be implemented with hashes - that's where the names come from - but their essence is hidden behind that part of their names.

Don't be confused by their names; they are deeply different things.

How do I remove objects from a JavaScript associative array?

The only working method for me:

function removeItem (array, value) {
    var i = 0;
    while (i < array.length) {
        if(array[i] === value) {
            array.splice(i, 1);
        } else {
    return array;


var new = removeItem( ["apple","banana", "orange"],  "apple");
// ---> ["banana", "orange"]

Avoid browser popup blockers

I tried multiple solutions, but his is the only one that actually worked for me in all the browsers

let newTab =; newTab.location.href = url;

What is "entropy and information gain"?

When I was implementing an algorithm to calculate the entropy of an image I found these links, see here and here.

This is the pseudo-code I used, you'll need to adapt it to work with text rather than images but the principles should be the same.

//Loop over image array elements and count occurrences of each possible
//pixel to pixel difference value. Store these values in prob_array
for j = 0, ysize-1 do $
    for i = 0, xsize-2 do begin
       diff = array(i+1,j) - array(i,j)
       if diff lt (array_size+1)/2 and diff gt -(array_size+1)/2 then begin
            prob_array(diff+(array_size-1)/2) = prob_array(diff+(array_size-1)/2) + 1

//Convert values in prob_array to probabilities and compute entropy
n = total(prob_array)

entrop = 0
for i = 0, array_size-1 do begin
    prob_array(i) = prob_array(i)/n

    //Base 2 log of x is Ln(x)/Ln(2). Take Ln of array element
    //here and divide final sum by Ln(2)
    if prob_array(i) ne 0 then begin
        entrop = entrop - prob_array(i)*alog(prob_array(i))

entrop = entrop/alog(2)

I got this code from somewhere, but I can't dig out the link.

Auto insert date and time in form input field?

$("#startDate").val($.datepicker.formatDate("dd/mm/yy", new Date()));
$("#endDate").val($.datepicker.formatDate("dd/mm/yy", new Date()));

Add the above code at the end of the script. This is required because the datepicker plugin has no provision to set the date in the control while initializing.

How do I replace a character in a string in Java?

Try using String.replace() or String.replaceAll() instead.

String my_new_str = my_str.replace("&", "&amp;");

(Both replace all occurrences; replaceAll allows use of regex.)

Why number 9 in kill -9 command in unix?

Both are same as kill -sigkill processID, kill -9 processID. Its basically for forced termination of the process.