Tutorial by Examples: ar

Basic complex arithmetic

Python has built-in support for complex arithmetic. The imaginary unit is denoted by j: z = 2+3j # A complex number w = 1-7j # Another complex number Complex numbers can be summed, subtracted, multiplied, divided and exponentiated: z + w # (3-4j) z - w # (1+10j) z * w # (23-11j) z / w # (...

Python Language • Complex math

What you see is NOT what you get: char vs cellstring in the command window

This a basic example aimed at new users. It does not focus on explaining the difference between char and cellstring. It might happen that you want to get rid of the ' in your strings, although you never added them. In fact, those are artifacts that the command window uses to distinguish between ...

MATLAB Language • Common mistakes and errors

Removing items from an array

Shift Use .shift to remove the first item of an array. For example: var array = [1, 2, 3, 4]; array.shift(); array results in: [2, 3, 4] Pop Further .pop is used to remove the last item from an array. For example: var array = [1, 2, 3]; array.pop(); array results in: [1, 2] Bot...

JavaScript • Arrays

Reversing arrays

.reverse is used to reverse the order of items inside an array. Example for .reverse: [1, 2, 3, 4].reverse(); Results in: [4, 3, 2, 1] Note: Please note that .reverse(Array.prototype.reverse) will reverse the array in place. Instead of returning a reversed copy, it will return the same ar...

JavaScript • Arrays

Using ShouldProcess() with one argument

if ($PSCmdlet.ShouldProcess("Target of action")) { # Do the thing } When using -WhatIf: What if: Performing the action "Invoke-MyCmdlet" on target "Target of action" When using -Confirm: Are you sure you want to perform this action? Performing operation &qu...

PowerShell • Using ShouldProcess

Declaration-site variance

Declaration-site variance can be thought of as declaration of use-site variance once and for all the use-sites. class Consumer<in T> { fun consume(t: T) { ... } } fun charSequencesConsumer() : Consumer<CharSequence>() = ... val stringConsumer : Consumer<String> = cha...

Kotlin • Generics

Use-site variance

Use-site variance is similar to Java wildcards: Out-projection: val takeList : MutableList<out SomeType> = ... // Java: List<? extends SomeType> val takenValue : SomeType = takeList[0] // OK, since upper bound is SomeType takeList.add(takenValue) // Error, lower bound for...

Kotlin • Generics

Why are there two build.gradle files in an Android Studio project?

<PROJECT_ROOT>\app\build.gradle is specific for app module. <PROJECT_ROOT>\build.gradle is a "Top-level build file" where you can add configuration options common to all sub-projects/modules. If you use another module in your project, as a local library you would have another...

Android • Gradle for Android

Declaring a property

At its simplest, a property is a function which returns a Bool. prop_reverseDoesNotChangeLength xs = length (reverse xs) == length xs A property declares a high-level invariant of a program. The QuickCheck test runner will evaluate the function with 100 random inputs and check that the result is...

Haskell Language • QuickCheck

Parsing strings into date-time objects

The functions for parsing a string into POSIXct and POSIXlt take similar parameters and return a similar-looking result, but there are differences in how that date-time is stored; see "Remarks." as.POSIXct("11:38", # time string format = "...

R Language • Date-time classes (POSIXct and POSIXlt)

Getting Started: Hello world!

Creating an HTML document and enabling knockout.js Create an HTML file and include knockout.js via a <script> tag. <!DOCTYPE html> <html> <head> <title>Hello world! (knockout.js)</title> </head> <body> <script src="https://cdnjs...

knockout.js • Getting started with knockout.js

BINARY and VARBINARY

Binary data types of either fixed length or variable length. Syntax: BINARY [ ( n_bytes ) ] VARBINARY [ ( n_bytes | max ) ] n_bytes can be any number from 1 to 8000 bytes. max indicates that the maximum storage space is 2^31-1. Examples: SELECT CAST(12345 AS BINARY(10)) -- 0x0000000000000000...

SQL • Data Types

CHAR and VARCHAR

String data types of either fixed length or variable length. Syntax: CHAR [ ( n_chars ) ] VARCHAR [ ( n_chars ) ] Examples: SELECT CAST('ABC' AS CHAR(10)) -- 'ABC ' (padded with spaces on the right) SELECT CAST('ABC' AS VARCHAR(10)) -- 'ABC' (no padding due to variable character) SELE...

SQL • Data Types

NCHAR and NVARCHAR

UNICODE string data types of either fixed length or variable length. Syntax: NCHAR [ ( n_chars ) ] NVARCHAR [ ( n_chars | MAX ) ] Use MAX for very long strings that may exceed 8000 characters.

SQL • Data Types

Converting NSArray to NSMutableArray to allow modification

NSArray *myColors = [NSArray arrayWithObjects: @"Red", @"Green", @"Blue", @"Yellow", nil]; // Convert myColors to mutable NSMutableArray *myColorsMutable = [myColors mutableCopy];

Objective-C Language • NSArray

Dictionary method changes

In Python 3, many of the dictionary methods are quite different in behaviour from Python 2, and many were removed as well: has_key, iter* and view* are gone. Instead of d.has_key(key), which had been long deprecated, one must now use key in d. In Python 2, dictionary methods keys, values and items ...

Python Language • Incompatibilities moving from Python 2 to Python 3

Extension methods aren't supported by dynamic code.

static class Program { static void Main() { dynamic dynamicObject = new ExpandoObject(); string awesomeString = "Awesome"; // Prints True Console.WriteLine(awesomeString.IsThisAwesome()); dynamicObject.StringValue = awesomeStrin...

C# Language • Extension Methods

Switch Statement with Regex Parameter

The -Regex parameter allows switch statements to perform regular expression matching against conditions. Example: switch -Regex ('Condition') { 'Con\D+ion' {'One or more non-digits'} 'Conditio*$' {'Zero or more "o"'} 'C.ndition' {'Any single char.'} '^C\w+ition$'...

PowerShell • Switch statement

Switch Statement with Wildcard Parameter

The -Wildcard parameter allows switch statements to perform wildcard matching against conditions. Example: switch -Wildcard ('Condition') { 'Condition' {'Normal match'} 'Condit*' {'Zero or more wildcard chars.'} 'C[aoc]ndit[f-l]on' {'Range and set of chars...

PowerShell • Switch statement

Switch Statement with Exact Parameter

The -Exact parameter enforces switch statements to perform exact, case-insensitive matching against string-conditions. Example: switch -Exact ('Condition') { 'condition' {'First Action'} 'Condition' {'Second Action'} 'conditioN' {'Third Action'} '^*ondition$' {'Fourth Action...

PowerShell • Switch statement