Tutorial by Examples: t

Filter a selection

To filter a selection you can use the .filter() method. The method is called on a selection and returns a new selection. If the filter matches an element then it is added to the returned selection, otherwise it is ignored. If no element is matched then an empty selection is returned. The HTML Thi...

jQuery • DOM Traversing

Repeating Annotations

Until Java 8, two instances of the same annotation could not be applied to a single element. The standard workaround was to use a container annotation holding an array of some other annotation: // Author.java @Retention(RetentionPolicy.RUNTIME) public @interface Author { String value(); } ...

Java Language • Annotations

Create composite index

This will create a composite index of both keys, mystring and mydatetime and speed up queries with both columns in the WHERE clause. CREATE INDEX idx_mycol_myothercol ON my_table(mycol, myothercol) Note: The order is important! If the search query does not include both columns in the WHERE claus...

MySQL • Indexes and Keys

The onBackpressureXXX operators

Most developers encounter backpressure when their application fails with MissingBackpressureException and the exception usually points to the observeOn operator. The actual cause is usually the non-backpressured use of PublishSubject, timer() or interval() or custom operators created via create(). ...

rx-java • Backpressure

Using a base template

base.twig.html <!DOCTYPE html> <html> <head> <title>{{ title | default('Hello World') }}</title> <link rel="stylesheet" type="text/css" href="theme.css"> {% block css %} {% endblock %} &...

twig • Template inheritance

Change the content of an included template

article.twig.html <article> <h1>{{ article.title }}</h1> {% block content %} <p>{{ article.content }}</p> {% endblock %} </article> articles.twig.html {# use default template for article #} {% for article in articles %} {% include &...

twig • Template inheritance

Monkey Patching

In this case, "monkey patching" means adding a new variable or method to a class after it's been defined. For instance, say we defined class A as class A(object): def __init__(self, num): self.num = num def __add__(self, other): return A(self.num + other.num)...

Python Language • Classes

Collections and Primitive Values

Collections in Java only work for objects. I.e. there is no Map<int, int> in Java. Instead, primitive values need to be boxed into objects, as in Map<Integer, Integer>. Java auto-boxing will enable transparent use of these collections: Map<Integer, Integer> map = new HashMap<&g...

Java Language • Collections

Checking if one array contains another array

public static class ArrayHelpers { public static bool Contains<T>(this T[] array, T[] candidate) { if (IsEmptyLocate(array, candidate)) return false; if (candidate.Length > array.Length) return false; for (int a = 0; a <...

C# Language • Arrays

Redis command line interface

redis-cli is the Redis command line interface program that allows to send commands to Redis and read the replies sent by the server, directly from the terminal. Basic command line usage is below: Access to redis: $ redis-cli 127.0.0.1:6379> Access to redis with authentication: $ redis-cli ...

redis • Getting started with redis

Listing All Class Members

The dir() function can be used to get a list of the members of a class: dir(Class) For example: >>> dir(list) ['__add__', '__class__', '__contains__', '__delattr__', '__delitem__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__...

Python Language • Classes

Install packages

Notice that packages can be installedThis command installs the newest available version of the named packages: both locally or globally. Local installation means that npm installs your package in the current working directory. Node modules go in ./node_modules, executables go in ./node_modules/.bi...

npm • Getting started with npm

Remove Whitespace from the Beginning and End of a String

The trim() method returns a new String with the leading and trailing whitespace removed. String s = new String(" Hello World!! "); String t = s.trim(); // t = "Hello World!!" If you trim a String that doesn't have any whitespace to remove, you will be returned the same S...

Java Language • Strings

Efficient pixel access using cv::Mat::ptr pointer

If efficiency is important, a fast way to iterate over pixels in a cv::Mat object is to use its ptr<T>(int r) method to obtain a pointer to the beginning of row r (0-based index). According to the matrix type, the pointer will have a different template. For CV_8UC1: uchar* ptr = image.ptr&...

opencv • Pixel Access

Installing Cython

To use Cython two things are needed.The Cython package itself, which contains the cython source-to-source compiler and Cython interfaces to several C and Python libraries (for example numpy). To compile the C code generated by the cython compiler, a C compiler is needed. Step 1: Installing Cython ...

cython • Getting started with cython

Private key is not accepted (OpenSSH clients debug)

By default, most of the information is hidden from the user. You can use -v switches to get a verbose log of the connection attempt, which will usually pinpoint the problem by showing why the behavior is different than you expect. Let's assume you are connecting to the server example.com using ssh ...

Secure Shell • Debugging ssh problems

Skipping some rows from result

ISO/ANSI SQL: SELECT Id, Col1 FROM TableName ORDER BY Id OFFSET 20 ROWS MySQL: SELECT * FROM TableName LIMIT 20, 42424242424242; -- skips 20 for take use very large number that is more than rows in table Oracle: SELECT Id, Col1 FROM (SELECT Id, Col1, row_num...

SQL • SKIP TAKE (Pagination)

Limiting amount of results

ISO/ANSI SQL: SELECT * FROM TableName FETCH FIRST 20 ROWS ONLY; MySQL; PostgreSQL; SQLite: SELECT * FROM TableName LIMIT 20; Oracle: SELECT Id, Col1 FROM (SELECT Id, Col1, row_number() over (order by Id) RowNumber FROM TableName) WHERE RowNumber <= 2...

SQL • SKIP TAKE (Pagination)

Skipping then taking some results (Pagination)

ISO/ANSI SQL: SELECT Id, Col1 FROM TableName ORDER BY Id OFFSET 20 ROWS FETCH NEXT 20 ROWS ONLY; MySQL: SELECT * FROM TableName LIMIT 20, 20; -- offset, limit Oracle; SQL Server: SELECT Id, Col1 FROM (SELECT Id, Col1, row_number() over (order by Id) RowNumbe...

SQL • SKIP TAKE (Pagination)

Getting Started

See also the Mercurial Tutorial Creating a Mercurial Repository A Mercurial repository is simply a directory (referred to as the "working directory") containing an .hg directory with metadata about the contents of the repository. This makes Mercurial very lightweight and easy to start us...

mercurial • Getting started with mercurial