Tutorial by Examples: g

Using lookbehind to test endings

A lookbehind can be used at the end of a pattern to ensure it ends or not in a certain way. ([a-z ]+|[A-Z ]+)(?<! ) matches sequences of only lowercase or only uppercase words while excluding trailing whitespace.

Regular Expressions • Lookahead and Lookbehind

Converting a string to a number

Number('0') === 0 Number('0') will convert the string ('0') into a number (0) A shorter, but less clear, form: +'0' === 0 The unary + operator does nothing to numbers, but converts anything else to a number. Interestingly, +(-12) === -12. parseInt('0', 10) === 0 parseInt('0', 10) will c...

JavaScript • Variable coercion/conversion

Converting a number to a string

String(0) === '0' String(0) will convert the number (0) into a string ('0'). A shorter, but less clear, form: '' + 0 === '0'

JavaScript • Variable coercion/conversion

Tabulating values - console.table()

In most environments, console.table() can be used to display objects and arrays in a tabular format. For example: console.table(['Hello', 'world']); displays like: (index)value0"Hello"1"world" console.table({foo: 'bar', bar: 'baz'}); displays like: (index)value"fo...

JavaScript • Console

ASP.NET Configure Await

When ASP.NET handles a request, a thread is assigned from the thread pool and a request context is created. The request context contains information about the current request which can be accessed through the static HttpContext.Current property. The request context for the request is then assigned t...

C# Language • Async/await, Backgroundworker, Task and Thread Examples

rgb() Notation

RGB is an additive color model which represents colors as mixtures of red, green, and blue light. In essence, the RGB representation is the decimal equivalent of the Hexadecimal Notation. In Hexadecimal each number ranges from 00-FF which is equivalent to 0-255 in decimal and 0%-100% in percentages....

CSS • Colors

"Promisifying" functions with callbacks

Given a function that accepts a Node-style callback, fooFn(options, function callback(err, result) { ... }); you can promisify it (convert it to a promise-based function) like this: function promiseFooFn(options) { return new Promise((resolve, reject) => fooFn(options, (err, re...

JavaScript • Promises

Using the @property decorator

The @property decorator can be used to define methods in a class which act like attributes. One example where this can be useful is when exposing information which may require an initial (expensive) lookup and simple retrieval thereafter. Given some module foobar.py: class Foo(object): def __...

Python Language • Property Objects

Handling InterruptedException

InterruptedException is a confusing beast - it shows up in seemingly innocuous methods like Thread.sleep(), but handling it incorrectly leads to hard-to-manage code that behaves poorly in concurrent environments. At its most basic, if an InterruptedException is caught it means someone, somewhere, c...

Java Language • Exceptions and exception handling

Using the @property decorator for read-write properties

If you want to use @property to implement custom behavior for setting and getting, use this pattern: class Cash(object): def __init__(self, value): self.value = value @property def formatted(self): return '${:.2f}'.format(self.value) @formatted.setter def ...

Python Language • Property Objects

Showcasing all common Angular constructs

The following example shows common AngularJS constructs in one file: <!DOCTYPE html> <html ng-app="myDemoApp"> <head> <style>.started { background: gold; }</style> <script src="https://code.angularjs.org/1.5.8/angular.min.js">&lt...

AngularJS • Getting started with AngularJS

Adding the total rows selected to every row

SELECT your_columns, COUNT(*) OVER() as Ttl_Rows FROM your_data_set idnameTtl_Rows1example52foo53bar54baz55quux5 Instead of using two queries to get a count then the line, you can use an aggregate as a window function and use the full result set as the window. This can be used as a base for fur...

SQL • Window Functions

Setting up a flag if other rows have a common property

Let's say I have this data: Table items idnametag1exampleunique_tag2foosimple42barsimple3bazhello51quuxworld I'd like to get all those lines and know if a tag is used by other lines SELECT id, name, tag, COUNT(*) OVER (PARTITION BY tag) > 1 AS flag FROM items The result will be: idnametag...

SQL • Window Functions

Getting a running total

Given this data: dateamount2016-03-122002016-03-11-502016-03-141002016-03-151002016-03-10-250 SELECT date, amount, SUM(amount) OVER (ORDER BY date ASC) AS running FROM operations ORDER BY date ASC will give you dateamountrunning2016-03-10-250-2502016-03-11-50-3002016-03-12200-1002016-03-1410...

SQL • Window Functions

Basic use and chaining

The pipe operator, %>%, is used to insert an argument into a function. It is not a base feature of the language and can only be used after attaching a package that provides it, such as magrittr. The pipe operator takes the left-hand side (LHS) of the pipe and uses it as the first argument of the ...

R Language • Pipe operators (%>% and others)

Check if a string matches a regular expression

3.0 Check if a string consists in exactly 8 digits: $ date=20150624 $ [[ $date =~ ^[0-9]{8}$ ]] && echo "yes" || echo "no" yes $ date=hello $ [[ $date =~ ^[0-9]{8}$ ]] && echo "yes" || echo "no" no

Bash • Pattern matching and regular expressions

Indenting here documents

You can indent the text inside here documents with tabs, you need to use the <<- redirection operator instead of <<: $ cat <<- EOF This is some content indented with tabs `\t`. You cannot indent with spaces you __have__ to use tabs. Bash will remove empty space befo...

Bash • Here documents and here strings

Here strings

2.05b You can feed a command using here strings like this: $ awk '{print $2}' <<< "hello world - how are you?" world $ awk '{print $1}' <<< "hello how are you > she is fine" hello she You can also feed a while loop with a here string: $ while IFS...

Bash • Here documents and here strings

Merging, combine and composing Maps

Use putAll to put every member of one map into another. Keys already present in the map will have their corresponding values overwritten. Map<String, Integer> numbers = new HashMap<>(); numbers.put("One", 1) numbers.put("Three", 3) Map<String, Integer> othe...

Java Language • Maps

Checking out a working copy

To begin making modifications to the project's data, you have to obtain a local copy of the versioned project. Use the command line svn client or your favorite SVN client (TortoiseSVN, for example). Your local copy of the project is called a working copy in Subversion and you get it by issuing the c...

svn • Getting started with svn