Tutorial by Examples: v

Getting a dictionary value

You can get the value of an entry in the dictionary using the 'Item' property: Dim extensions As New Dictionary(Of String, String) From { { "txt", "notepad" }, { "bmp", "paint" }, { "doc", "winword" } } Dim program As St...

Visual Basic .NET Language • Dictionaries

Navigating in cmd

One of the most common things you'll need to do in the command prompt is navigate your file system. To do this, we'll utilize the cd and dir keywords. Start by opening up a command prompt using one of the methods mentioned here. You most likely see something similar to what's below, where UserNam...

cmd • Getting started with cmd

Vectors

Vectors in R can have different types (e.g. integer, logical, character). The most general way of defining a vector is by using the function vector(). vector('integer',2) # creates a vector of integers of size 2. vector('character',2) # creates a vector of characters of size 2. vector('logical',2...

R Language • Creating vectors

Basic directive with template and an isolated scope

Creating a custom directive with isolated scope will separate the scope inside the directive from the outside scope, in order to prevent our directive from accidentally change the data in the parent scope and restricting it from reading private data from the parent scope. To create an isolated scop...

AngularJS • Custom Directives

Convert to string

Use Kernel.inspect to convert anything to string. iex> Kernel.inspect(1) "1" iex> Kernel.inspect(4.2) "4.2" iex> Kernel.inspect %{pi: 3.14, name: "Yos"} "%{pi: 3.14, name: \"Yos\"}"

Elixir Language • Strings

Lists as a convention

Some languages include a list data structure. Common Lisp, and other languages in the Lisp family, make extensive use of lists (and the name Lisp is based on the idea of a LISt Processor). However, Common Lisp doesn't actually include a primitive list datatype. Instead, lists exist by convention....

common-lisp • Cons cells and lists

Invalidating a timer

Swift timer.invalidate() Objective-C [timer invalidate]; This will stop the timer from firing. Must be called from the thread the timer was created in, see Apple's notes: You must send this message from the thread on which the timer was installed. If you send this message from another thr...

iOS • NSTimer

Truth Values

The following values are considered falsey, in that they evaluate to False when applied to a boolean operator. None False 0, or any numerical value equivalent to zero, for example 0L, 0.0, 0j Empty sequences: '', "", (), [] Empty mappings: {} User-defined types where the __bool__ o...

Python Language • Conditionals

Using overlap

This query gets all overlapping appointments from six to ten. Appointment.objects.filter(time_span__overlap=(6, 10))

Django • RangeFields - a group of PostgreSQL specific fields

Removing extraneous packages

To remove extraneous packages (packages that are installed but not in dependency list) run the following command: npm prune To remove all dev packages add --production flag: npm prune --production More on it

Node.js • npm

Remove duplicate values in list

Removing duplicate values in a list can be done by converting the list to a set (that is an unordered collection of distinct objects). If a list data structure is needed, then the set can be converted back to a list using the function list(): names = ["aixk", "duke", "edik&...

Python Language • List

Using external variables

It is possible, inside a closure, to use an external variable with the special keyword use. For instance: <?php $quantity = 1; $calculator = function($number) use($quantity) { return $number + $quantity; }; var_dump($calculator(2)); // Shows "3" You can go further by ...

PHP • Closure

Use closures to implement observer pattern

In general, an observer is a class with a specific method being called when an action on the observed object occurs. In certain situations, closures can be enough to implement the observer design pattern. Here is a detailed example of such an implementation. Let's first declare a class whose purpos...

PHP • Closure

Moving HEAD

When you run git checkout on a commit (specified by hash or ref) you're telling git to make your working directory look like how it did when the snapshot was taken. Update the files in the working directory to match the tree inside the commit Update HEAD to point to the specified hash or ref ...

Git • Internals

Moving refs around

Running git reset --hard moves refs to the specified hash/ref. Moving MyBranch to b8dc53: $ git checkout MyBranch # moves HEAD to MyBranch $ git reset --hard b8dc53 # makes MyBranch point to b8dc53