Tutorial by Examples: r

Subquery in SELECT clause

SELECT Id, FName, LName, (SELECT COUNT(*) FROM Cars WHERE Cars.CustomerId = Customers.Id) AS NumberOfCars FROM Customers

SQL • Subqueries

Macros allow us to abstract syntactical patterns that are repeated many times. For instance: /// Computes `a + b * c`. If any of the operation overflows, returns `None`. fn checked_fma(a: u64, b: u64, c: u64) -> Option<u64> { let product = match b.checked_mul(c) { Some(p) =&...

Rust • Macros

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

Reading and writing to a file using ioutil

A simple program that writes "Hello, world!" to test.txt, reads back the data, and prints it out. Demonstrates simple file I/O operations. package main import ( "fmt" "io/ioutil" ) func main() { hello := []byte("Hello, world!") //...

Go • File I/O

Listing all the files and folders in the current directory

package main import ( "fmt" "io/ioutil" ) func main() { files, err := ioutil.ReadDir(".") if err != nil { panic(err) } fmt.Println("Files and folders in the current directory:") for _, fileInfo := range fi...

Go • File I/O

Accessing class members

To access member variables and member functions of an object of a class, the . operator is used: struct SomeStruct { int a; int b; void foo() {} }; SomeStruct var; // Accessing member variable a in var. std::cout << var.a << std::endl; // Assigning member variable b in v...

C++ • Classes/Structures

Creating a pure JSON table

To create a pure JSON table you need to provide a single field with the type JSONB: CREATE TABLE mytable (data JSONB NOT NULL); You should also create a basic index: CREATE INDEX mytable_idx ON mytable USING gin (data jsonb_path_ops); At this point you can insert data in to the table and que...

postgresql • JSON Support

Querying complex JSON documents

Taking a complex JSON document in a table: CREATE TABLE mytable (data JSONB NOT NULL); CREATE INDEX mytable_idx ON mytable USING gin (data jsonb_path_ops); INSERT INTO mytable VALUES($$ { "name": "Alice", "emails": [ "[email protected]", ...

postgresql • JSON Support

Create a Button

Creation of a Button is simple: Button sampleButton = new Button(); This will create a new Button without any text or graphic inside. If you want to create a Button with a text, simply use the constructor that takes a String as parameter (which sets the textProperty of the Button): Button samp...

javafx • Button

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

Installation or Setup

The D programming language's standard compiler DMD can run on all major platforms. To install DMD see here. To install by command line you may run the command (found on the D website): curl -fsS https://dlang.org/install.sh | bash -s dmd Package Managers Arch Linux pacman -S dlang Chocolate...

D Language • Getting started with D Language

Formatted strings

Ruby can inject an array of values into a string by replacing any placeholders with the values from the supplied array. "Hello %s, my name is %s!" % ['World', 'br3nt'] # => Hello World, my name is br3nt! The place holders are represented by two %s and the values are supplied by the...

Ruby Language • Strings

Repeat a String n times

Problem: Create a String containing n repetitions of a String s. The trivial approach would be repeatedly concatenating the String final int n = ... final String s = ... String result = ""; for (int i = 0; i < n; i++) { result += s; } This creates n new string instances ...

Java Language • StringBuilder

Installation or Setup

SWI-Prolog Windows and Mac: Download SWI-Prolog at the official website Simply install by following the installer instructions. Linux (PPA): Add the PPA ppa:swi-prolog/stable to your system’s software sources (developers may choose for ppa:swi-prolog/devel) : Open a terminal (Ctrl+...

Prolog Language • Getting started with Prolog Language

Installation or Setup

If you don't have any RubyGems installed, there is still the pre-gem approach to getting software, doing it manually: Download from RubyGems Unpack into a directory and cd there Install with: ruby setup.rb (you may need admin/root privilege) sudo ruby setup.rb For more details...

rubygems • Getting started with rubygems

Pattern Matching with Case Classes

Every case class defines an extractor that can be used to capture the members of the case class when pattern matching: case class Student(name: String, email: String) def matchStudent1(student: Student): String = student match { case Student(name, email) => s"$name has the following...

Scala Language • Pattern Matching

Basic Info and String Concatenation

Strings in JavaScript can be enclosed in Single quotes 'hello', Double quotes "Hello" and (from ES2015, ES6) in Template Literals (backticks) `hello`. var hello = "Hello"; var world = 'world'; var helloW = `Hello World`; // ES2015 / ES6 Strings can be created...

JavaScript • Strings

Requiring multiple upper bounds ("extends A & B")

You can require a generic type to extend multiple upper bounds. Example: we want to sort a list of numbers but Number doesn't implement Comparable. public <T extends Number & Comparable<T>> void sortNumbers( List<T> n ) { Collections.sort( n ); } In this example T must...

Java Language • Generics

Set attributed text

// Modify some of the attributes of the attributed string. let attributedText = NSMutableAttributedString(attributedString: textView.attributedText!) // Use NSString so the result of rangeOfString is an NSRange. let text = textView.text! as NSString // Find the range of each element to modif...

iOS • UITextView

Change text color

Swift textView.textColor = UIColor.red Objective-C textView.textColor = [UIColor redColor];

iOS • UITextView