Tutorial by Examples: p

Iterating over the entries of a hash table with maphash

(defun print-entry (key value) (format t "~A => ~A~%" key value)) (maphash #'print-entry *my-table*) ;; => NIL Using maphash allows to iterate over the entries of a hash table. The order of iteration is unspecified. The first argument is a function accepting two parameters: ...

common-lisp • Hash tables

Map and Filter Over A Collection

Map 'Mapping' across a collection uses the map function to transform each element of that collection in a similar way. The general syntax is: val someFunction: (A) => (B) = ??? collection.map(someFunction) You can provide an anonymous function: collection.map((x: T) => /*Do something wi...

Scala Language • Collections

Namespace variables

The variable command ensures that a given namespace variable is created. Until a value is assigned to it, the variable's value is undefined: namespace eval mynamespace { variable alpha set alpha 0 } The variable can be accessed from outside the namespace (from anywhere, in fact) by at...

tcl • Variables

Deploying your application

Make sure you are in the directory that contains your Rails app, then create an app on Heroku. $ heroku create example Creating ⬢ example... done https://example.herokuapp.com/ | https://git.heroku.com/example.git The first URL of the ouput, http://example.herokuapp.com, is the location the ap...

Ruby on Rails • Deploying a Rails app on Heroku

Checking the syntax of a script with "-n"

The -n flag enables you to check the syntax of a script without having to execute it: ~> $ bash -n testscript.sh testscript.sh: line 128: unexpected EOF while looking for matching `"' testscript.sh: line 130: syntax error: unexpected end of file

Bash • Debugging

Installation or Setup

Download and install the WiX Toolset from wixtoolset.org. The installer for the WiX Toolset provides also the integration with Visual Studio, after the installation you should be able to create WiX specific projects. Warnings Admin rights are needed. Some versions of WiX are compatible only with...

wix • Getting started with wix

Installation or Setup

Detailed instructions on getting asp.net-identity set up or installed.

asp.net-identity • Getting started with asp.net-identity

Gradle Parallel builds

Gradle will only run one task at a time by default, regardless of the project structure. By using the --parallel switch, you can force Gradle to execute independent subprojects - those that have no implicit or explicit project dependencies between one another - in parallel, allowing it to run multip...

gradle • Gradle Performance

Split routes into multiple files

If your routes file is overwhelmingly big, you can put your routes in multiple files and include each of the files with Ruby’s require_relative method: config/routes.rb: YourAppName::Application.routes.draw do require_relative 'routes/admin_routes' require_relative 'routes/sidekiq_routes' ...

Ruby on Rails • Routing

Installation or Setup

On Windows Download the Visual Studio Code installer for Windows. Once it is downloaded, run the installer (VSCodeSetup-version.exe). This will only take a minute. By default, VS Code is installed under C:\Program Files (x86)\Microsoft VS Code for a 64-bit machine. Note: .NET Framework 4.5.2...

vscode • Getting started with vscode

Newline character is not consumed in typical scanf() call

When this program #include <stdio.h> #include <string.h> int main(void) { int num = 0; char str[128], *lf; scanf("%d", &num); fgets(str, sizeof(str), stdin); if ((lf = strchr(str, '\n')) != NULL) *lf = '\0'; printf("%d \"%s\&...

C Language • Common pitfalls

Asset packages

Asset Packages (with the file format of .unitypackage) are a commonly used way of distributing Unity projects to other users. When working with peripherals that have their own SDKs (eg. Oculus), you may be asked to download and import one of these packages. Importing a .unitypackage To import a pa...

unity3d • How to use asset packages

Minimal Chart Example

Depending on the version of Chart.JS you are using (the current one being 2.X), the syntax is different to create a minimal example of a bar chart (JSFiddle Demo for 2.X). Chart.js 2.X <html> <body> <canvas id="myChart" width="400" height="400&...

chart.js • Getting started with chart.js

Initial project workflow

Create a new project dotnet new -l f# Restore any packages listed in project.json dotnet restore A project.lock.json file should be written out. Execute the program dotnet run The above will compile the code if required. The output of the default project created by dotnet new -l f# con...

F# • F# on .NET Core

Espresso custom matchers

Espresso by default has many matchers that help you find views that you need to do some checks or interactions with them. Most important ones can be found in the following cheat sheet: https://google.github.io/android-testing-support-library/docs/espresso/cheatsheet/ Some examples of matchers are...

Android • Testing UI with Espresso

Presenting UI with setContentView

Activity class takes care of creating a window for you in which you can place your UI with setContentView. There are three setContentView methods: setContentView(int layoutResID) - Set the activity content from a layout resource. setContentView(View view) - Set the activity content to an explic...

Android • Activity

Natural (comparable) vs explicit (comparator) sorting

There are two Collections.sort() methods: One that takes a List<T> as a parameter where T must implement Comparable and override the compareTo() method that determines sort order. One that takes a List and a Comparator as the arguments, where the Comparator determines the sort order. ...

Java Language • Comparable and Comparator

Optimization Example (golden)

The 'Golden' method minimizes a unimodal function by narrowing the range in the extreme values import numpy as np from scipy.optimize import _minimize from scipy import special import matplotlib.pyplot as plt x = np.linspace(0, 10, 500) y = special.j0(x) optimize.minimize_scalar(special.j0,...

scipy • How to write a Jacobian function for optimize.minimize

Optimization Example (Brent)

Brent's method is a more complex algorithm combination of other root-finding algorithms; however, the resulting graph isn't much different from the graph generated from the golden method. import numpy as np import scipy.optimize as opt from scipy import special import matplotlib.pyplot as plt ...

scipy • How to write a Jacobian function for optimize.minimize

Cross Platform OpenGL context creation (using SDL2)

Creating a Window with OpenGL context (extension loading through GLEW): #define GLEW_STATIC #include <GL/glew.h> #include <SDL2/SDL.h> int main(int argc, char* argv[]) { SDL_Init(SDL_INIT_VIDEO); /* Initialises Video Subsystem in SDL */ /* Setting up OpenGL version a...

opengl • Getting started with opengl