Tutorial by Examples: ar

Guards (if expressions)

Case statements can be combined with if expressions to provide extra logic when pattern matching. def checkSign(x: Int): String = { x match { case a if a < 0 => s"$a is a negative number" case b if b > 0 => s"$b is a positive number" case c ...

Scala Language • Pattern Matching

Declaring namespaces

A namespace declaration can look as follows: namespace MyProject; - Declare the namespace MyProject namespace MyProject\Security\Cryptography; - Declare a nested namespace namespace MyProject { ... } - Declare a namespace with enclosing brackets. It is recommended to only declare a single na...

PHP • Namespaces

Parsing HTML from a string

PHP implements a DOM Level 2 compliant parser, allowing you to work with HTML using familiar methods like getElementById() or appendChild(). $html = '<html><body><span id="text">Hello, World!</span></body></html>'; $doc = new DOMDocument(); libxml_u...

PHP • Parsing HTML

Installation of scikit-learn

The current stable version of scikit-learn requires: Python (>= 2.6 or >= 3.3), NumPy (>= 1.6.1), SciPy (>= 0.9). For most installation pip python package manager can install python and all of its dependencies: pip install scikit-learn However for linux systems it is recomm...

scikit-learn • Getting started with scikit-learn

Declaring a constant

Constants are declared like variables, but using the const keyword: const Greeting string = "Hello World" const Years int = 10 const Truth bool = true Like for variables, names starting with an upper case letter are exported (public), names starting with lower case are not. // not e...

Go • Constants

Array Modification

Change Index Initialize or update a particular element in the array array[10]="elevenths element" # because it's starting with 0 3.1 Append Modify array, adding elements to the end if no subscript is specified. array+=('fourth element' 'fifth element') Replace the entire ar...

Bash • Arrays

Parsing JSON with Gson

The example shows parsing a JSON object using the Gson library from Google. Parsing objects: class Robot { //OPTIONAL - this annotation allows for the key to be different from the field name, and can be omitted if key and field name are same . Also this is good coding practice as it decouple ...

Android • Gson

Comparison start of line anchor and start of string anchor

While many people think that ^ means the start of a string, it actually means start of a line. For an actual start of string anchor use, \A. The string hello\nworld (or more clearly) hello world Would be matched by the regular expressions ^h, ^w and \Ah but not by \Aw

Regular Expressions • Anchor Characters: Caret (^)

Copying arrays

Java provides several ways to copy an array. for loop int[] a = { 4, 1, 3, 2 }; int[] b = new int[a.length]; for (int i = 0; i < a.length; i++) { b[i] = a[i]; } Note that using this option with an Object array instead of primitive array will fill the copy with reference to the origi...

Java Language • Arrays

Concatenating Arrays

Two Arrays var array1 = [1, 2]; var array2 = [3, 4, 5]; 3 var array3 = array1.concat(array2); // returns a new array 6 var array3 = [...array1, ...array2] Results in a new Array: [1, 2, 3, 4, 5] Multiple Arrays var array1 = ["a", "b"], array2 = ["...

JavaScript • Arrays

Append / Prepend items to Array

Unshift Use .unshift to add one or more items in the beginning of an array. For example: var array = [3, 4, 5, 6]; array.unshift(1, 2); array results in: [1, 2, 3, 4, 5, 6] Push Further .push is used to add items after the last currently existent item. For example: var array = [1, 2, 3...

JavaScript • Arrays

Object keys and values to array

var object = { key1: 10, key2: 3, key3: 40, key4: 20 }; var array = []; for(var people in object) { array.push([people, object[people]]); } Now array is [ ["key1", 10], ["key2", 3], ["key3", 40], ["key4", 20] ] ...

JavaScript • Arrays

Sorting multidimensional array

Given the following array var array = [ ["key1", 10], ["key2", 3], ["key3", 40], ["key4", 20] ]; You can sort it sort it by number(second index) array.sort(function(a, b) { return a[1] - b[1]; }) 6 array.sort((a,b) => a[1] - b[1]);...

JavaScript • Arrays

Arithmetic Operators

1 + 2 # Addition 1 - 2 # Subtraction -1 # Set negative value 1 * 2 # Multiplication 1 / 2 # Division 1 % 2 # Modulus 100 -shl 2 # Bitwise Shift-left 100 -shr 1 # Bitwise Shift-right

PowerShell • Operators

Comparison Operators

PowerShell comparison operators are comprised of a leading dash (-) followed by a name (eq for equal, gt for greater than, etc...). Names can be preceded by special characters to modify the behavior of the operator: i # Case-Insensitive Explicit (-ieq) c # Case-Sensitive Explicit (-ceq) Case-I...

PowerShell • Operators

Use with parameter

class Animal def method_missing(method, *args, &block) say, speak = method.to_s.split("_") if say == "say" && speak return speak.upcase if args.first == "shout" speak else super end end end => Animal.new....

Ruby Language • method_missing

Allocatable arrays

Arrays can have the allocatable attribute: ! One dimensional allocatable array integer, dimension(:), allocatable :: foo ! Two dimensional allocatable array real, dimension(:,:), allocatable :: bar This declares the variable but does not allocate any space for it. ! We can specify the bounds...

Fortran • Arrays

Add a reference column to a table

To add a reference to a team to the users table, run this command: $ rails generate migration AddTeamRefToUsers team:references This generates the following migration: class AddTeamRefToUsers < ActiveRecord::Migration[5.0] def change add_reference :users, :team, foreign_key: true ...

Ruby on Rails • ActiveRecord Migrations

Single character match

To broaden the selections of a structured query language (SQL-SELECT) statement, wildcard characters, the percent sign (%) and the underscore (_), can be used. The _ (underscore) character can be used as a wildcard for any single character in a pattern match. Find all employees whose Fname start w...

SQL • LIKE operator

Declaring a HashSet with values

You can create a new class that inherits from HashSet: Set<String> h = new HashSet<String>() {{ add("a"); add("b"); }}; One line solution: Set<String> h = new HashSet<String>(Arrays.asList("a", "b")); Using guava: Se...

Java Language • Sets