Tutorial by Examples: for

Negation normal form : deep pattern matching

Pattern matching allows to deconstruct complex values and it is by no way limited to the “outer most” level of the representation of a value. To illustrate this, we implement the function transforming a boolean expression into a boolean expression where all negations are only on atoms, the so calle...

OCaml • Pattern Matching

For

for loops are simplified syntax for a very common loop pattern, which could be accomplished in more lines with a while loop. The following is a common example of a for loop, which will execute 100 times and then stop. for (int i = 0; i < 100; i++) { // do something } This is equivalen...

arduino • Loops

Undefined Function or Method X for Input Arguments of Type Y

This is MATLAB's long-winded way of saying that it cannot find the function that you're trying to call. There are a number of reasons you could get this error: That function was introduced after your current version of MATLAB The MATLAB online documentation provides a very nice feature which allow...

MATLAB Language • Common mistakes and errors

Log for a range of lines within a file

$ git log -L 1,20:index.html commit 6a57fde739de66293231f6204cbd8b2feca3a869 Author: John Doe <[email protected]> Date: Tue Mar 22 16:33:42 2016 -0500 commit message diff --git a/index.html b/index.html --- a/index.html +++ b/index.html @@ -1,17 +1,20 @@ <!DOCTYPE HTML> ...

Git • Browsing the history

Taking a screenshot and video (for kitkat only) from a device display

Screen shot: Option 1 (pure adb) The shell adb command allows us to execute commands using a device's built-in shell. The screencap shell command captures the content currently visible on a device and saves it into a given image file, e.g. /sdcard/screen.png: adb shell screencap /sdcard/screen.png...

Android • ADB (Android Debug Bridge)

Forbid null values

To forbid null values in your table columns, add the :null parameter to your migration, like this: class AddPriceToProducts < ActiveRecord::Migration def change add_column :products, :float, null: false end end

Ruby on Rails • ActiveRecord Migrations

Using FOR XML to Concatenate Values from Multiple Rows

One common use for the FOR XML function is to concatenate the values of multiple rows. Here's an example using the Customers table: SELECT STUFF( (SELECT ';' + Email FROM Customers where (Email is not null and Email <> '') ORDER BY Email ASC FOR XM...

Microsoft SQL Server • The STUFF Function

Use transform and opacity to avoid trigger layout

Changing some CSS attribute will trigger the browser to synchronously calculate the style and layout, which is a bad thing when you need to animate at 60fps. DON'T Animate with left and top trigger layout. #box { left: 0; top: 0; transition: left 0.5s, top 0.5s; position: absolute; ...

CSS • Performance

Installation of AWS CLI for accessing S3

Installing aws cli in Ubuntu / Debian Instance sudo apt-get install -y python-dev python-pip sudo pip install awscli aws --version aws configure Installing aws cli using python Using pip you can install aws cli in windows, OS X and Linux sudo pip install awscli Configuring the AWS Comman...

amazon-s3 • Getting started with amazon-s3

Desugaring For Comprehensions

for comprehensions in Scala are just syntactic sugar. These comprehensions are implemented using the withFilter, foreach, flatMap and map methods of their subject types. For this reason, only types that have these methods defined can be utilized in a for comprehension. A for comprehension of the fo...

Scala Language • For Expressions

Reasons for using lists

To the average R user, the list structure may appear to be the one of the more complicated data structures to manipulate. There are no guarantees that all the elements within it are of the same type; There is no guaranteed structure of how complicated/non-complicated that the list would be (An eleme...

R Language • Lists

System Locale Information

+currentCalendar returns the logical calendar for the current user. NSCalendar *calender = [NSCalendar currentCalendar]; NSLog(@"%@",calender); +autoupdatingCurrentCalendar returns the current logical calendar for the current user. NSCalendar *calender = [NSCalendar autoupdat...

Objective-C Language • NSCalendar

Typical usage and reasons for using ob_start

ob_start is especially handy when you have redirections on your page. For example, the following code won't work: Hello! <?php header("Location: somepage.php"); ?> The error that will be given is something like: headers already sent by <xxx> on line <xxx>. In or...

PHP • Output Buffering

Reshape from long to wide format with spread()

library(tidyr) ## example data set.seed(123) df <- data.frame( name = rep(c("firstName", "secondName"), each=4), numbers = rep(1:4, 2), value = rnorm(8) ) df # name numbers value # 1 firstName 1 -0.56047565 # 2 firstName 2 -0.2301...

R Language • Reshape using tidyr

Basic request format

In HTTP 1.1, a minimal HTTP request consists of a request line and a Host header: GET /search HTTP/1.1 \r\n Host: google.com \r\n \r\n The first line has this format: Method Request-URI HTTP-Version CRLF Method should be a valid HTTP method; one of [1][2]: OPTIONS GET HEAD POST PUT ...

HTTP • HTTP requests

Prompting for Credentials

To prompt for credentials, you should almost always use the Get-Credential cmdlet: $credential = Get-Credential Pre-filled user name: $credential = Get-Credential -UserName 'myUser' Add a custom prompt message: $credential = Get-Credential -Message 'Please enter your company email address a...

PowerShell • Handling Secrets and Credentials

Getting file information

Check if a path is a directory or a file The is_dir function returns whether the argument is a directory, while is_file returns whether the argument is a file. Use file_exists to check if it is either. $dir = "/this/is/a/directory"; $file = "/this/is/a/file.txt"; echo is_d...

PHP • File handling