Tutorial by Examples: r

Use class introspection

You can use a class to mimic the switch/case structure. The following is using introspection of a class (using the getattr() function that resolves a string into a bound method on an instance) to resolve the "case" part. Then that introspecting method is aliased to the __call__ method to ...

Python Language • Alternatives to switch statement from other languages

Using a context manager

Another way, which is very readable and elegant, but far less efficient than a if/else structure, is to build a class such as follows, that will read and store the value to compare with, expose itself within the context as a callable that will return true if it matches the stored value: class Switc...

Python Language • Alternatives to switch statement from other languages

Differences between inner/outer joins

SQL has various join types to specify whether (non-)matching rows are included in the result: INNER JOIN, LEFT OUTER JOIN, RIGHT OUTER JOIN, and FULL OUTER JOIN (the INNER and OUTER keywords are optional). The figure below underlines the differences between these types of joins: the blue area repres...

SQL • JOIN

Basic GROUP BY example

It might be easier if you think of GROUP BY as "for each" for the sake of explanation. The query below: SELECT EmpID, SUM (MonthlySalary) FROM Employee GROUP BY EmpID is saying: "Give me the sum of MonthlySalary's for each EmpID" So if your table looked like this: +----...

SQL • GROUP BY

Preprocessing

Pre-processing in caret is done through the preProcess() function. Given a matrix or data frame type object x, preProcess() applies transformations on the training data which can then be applied to testing data. The heart of the preProcess() function is the method argument. Method operations are ap...

R Language • caret

Performing an action on a view

It is possible to perform ViewActions on a view using the perform method. The ViewActions class provides helper methods for the most common actions, like: ViewActions.click() ViewActions.typeText() ViewActions.clearText() For example, to click on the view: onView(...).perform(click()); onVi...

Android • Testing UI with Espresso

Inheritance Modifiers (on classes)

Inherits Specifies the base (or parent) class Public Class Person End Class Public Class Customer Inherits Person End Class 'One line notation Public Class Student : Inherits Person End Class Possible objects: Dim p As New Person Dim c As New Customer Dim s As New Student ...

Visual Basic .NET Language • OOP Keywords

Inheritance Modifiers (on properties and methods)

Overridable Allows a property or method in a class to be overridden in a derived class. Public Class Person Public Overridable Sub DoSomething() Console.WriteLine("Person") End Sub End Class Overrides Overrides an Overridable property or method defined in the base...

Visual Basic .NET Language • OOP Keywords

Overloading

Overloading is the creation of more than one procedure, instance constructor, or property in a class with the same name but different argument types. Class Person Overloads Sub Display(ByVal theChar As Char) ' Add code that displays Char data. End Sub Overloads Sub Display...

Visual Basic .NET Language • OOP Keywords

Interfaces

Public Interface IPerson Sub DoSomething() End Interface Public Class Customer Implements IPerson Public Sub DoSomething() Implements IPerson.DoSomething Console.WriteLine("Customer") End Sub End Class

Visual Basic .NET Language • OOP Keywords

Installation or Setup

Chart.js can be included in several different ways: NPM Run the following command on your NPM project directory npm install chart.js --save CDN Include a script tag in your HTML linking to the chart.js CDN <html> <body> <script type="text/javascript" s...

chart.js • Getting started with chart.js

Using character constants instead of string literals, and vice versa

In C, character constants and string literals are different things. A character surrounded by single quotes like 'a' is a character constant. A character constant is an integer whose value is the character code that stands for the character. How to interpret character constants with multiple charac...

C Language • Common pitfalls

How to know the directory and/or the path of the file you are editing

To know the path of the directory your file is in you can use: Esc to enter command mode :pwd This will print the path to the directory at the bottom of the editor, like this I'm a ninja ~ ~ ~ ~ ~ /home/ubuntu/myfolder 1,5 All Now...

vim • Tips and tricks to boost productivity

Download a file from Server using Retrofit2

Interface declaration for downloading a file public interface ApiInterface { @GET("movie/now_playing") Call<MovieResponse> getNowPlayingMovies(@Query("api_key") String apiKey, @Query("page") int page); // option 1: a resource relative to your bas...

Android • Retrofit2

Replace

Returns a string (varchar or nvarchar) where all occurrences of a specified sub string is replaced with another sub string. Parameters: string expression. This is the string that would be searched. It can be a character or binary data type. pattern. This is the sub string that would be replaced...

Microsoft SQL Server • String Functions

Sample to get user profile path

# will retrieve my home path ENV['HOME'] # => "/Users/username" # will try retrieve the 'FOO' environment variable. If failed, will get 'bar' ENV.fetch('FOO', 'bar')

Ruby Language • Environment Variables

Introduction

Ruby has three types of objects: Classes and modules which are instances of class Class or class Module. Instances of classes. Singleton Classes. Each object has a class which contains its methods: class Example end object = Example.new object.class # => Example Example.class # ...

Ruby Language • Singleton Class

Accessing Instance/Class Variables in Singleton Classes

Singleton classes share their instance/class variables with their object. class Example @@foo = :example end def Example.foo class_variable_get :@@foo end Example.foo #=> :example class Example def initialize @foo = 1 end def foo @foo end end e = Ex...

Ruby Language • Singleton Class

Delete a range of lines into a named register

In Normal, type the following to delete a range of lines into a named register :10,20d a This will delete lines 10,20 in register "a. We can verify this by typing :reg This will show the text that was delete in register "a. To paste the contents in "a, just type "ap ...

vim • Vim Registers

Formatting console output

Many of the console's print methods can also handle C-like string formatting, using % tokens: console.log('%s has %d points', 'Sam', 100); Displays Sam has 100 points. The full list of format specifiers in Javascript is: SpecifierOutput%sFormats the value as a string%i or %dFormats the value a...

JavaScript • Console