Tutorial by Examples: r

The coordinate systems of Matplotlib come very handy when trying to annotate the plots you make. Sometimes you would like to position text relatively to your data, like when trying to label a specific point. Other times you would maybe like to add a text on top of the figure. This can easily be achi...

In order for a program to react to a certain signal, other than using default action, custom signal handler can be installed using sigaction. sigaction receives three arguments - signal to act on, pointer to sigaction_t structure which, if not NULL, is describing new behaviour and pointer to sigacti...

A string is a sequence of character literals. To date, strings are supported by all modern programming languages,1 but there is no consensus between language designers on how strings should be classified. As far as programming language design is concerned there are two primary concerns to take into ...

SELECT DATE('2003-12-31 01:02:03'); The output will be: 2003-12-31

Least squares is a standard approach to problems with more equations than unknowns, also known as overdetermined systems. Consider the four equations: x0 + 2 * x1 + x2 = 4 x0 + x1 + 2 * x2 = 3 2 * x0 + x1 + x2 = 5 x0 + x1 + x2 = 4 We can express this as a matrix multiplication A * x = b: A ...

When rendering a form 'by hand', it can be useful to know if there are fields left to render or not. The function isRendered() from the FormView class returns true if there are still fields left to be rendered to the template. This snippet prints <h3>Extra fields</h3> if there are fiel...

Group Concat is used in MySQL to get concatenated values of expressions with more than one result per column. Meaning, there are many rows to be selected back for one column such as Name(1):Score(*) NameScoreAdamA+AdamA-AdamBAdamC+BillD-JohnA- SELECT Name, GROUP_CONCAT(Score ORDER BY Score desc SE...

CREATE TABLE foo ( ... name CHARACTER SET utf8mb4 ... );

There are dozens of character sets with hundreds of collations. (A given collation belongs to only one character set.) See the output of SHOW COLLATION;. There are usually only 4 CHARACTER SETs that matter: ascii -- basic 7-bit codes. latin1 -- ascii, plus most characters needed for Western Eur...

Use git revert to revert existing commits, especially when those commits have been pushed to a remote repository. It records some new commits to reverse the effect of some earlier commits, which you can push safely without rewriting history. Don't use git push --force unless you wish to bring down ...

You can rename branch in local repository using this command: git branch -m old_name new_name

Getting zsh zsh is available on many UNIX-like platforms via their built-in package management systems. On the Debian and Ubuntu Linux distributions, zsh is available in the default package repositories and can be installed using: $ sudo apt-get install zsh # or, on newer Ubuntu distributions $ ...

You can obtain the url for an existing remote by using the command git remote get-url <name> By default, this will be git remote get-url origin

There are several packages that allow the output of data structures in form of HTML or LaTeX tables. They mostly differ in flexibility. Here I use the packages: knitr xtable pander For HTML documents --- title: "Printing Tables" author: "Martin Schmelzer" date: &quot...

C++ thrives on what is known as a Regular type (or at least Pseudo-Regular). A Regular type is a type that can be constructed and assigned-to and assigned-from via copy or move, can be destroyed, and can be compared equal-to. It can also be constructed from no arguments. Finally, it also has supp...

If everything whas been set up correctly, the following snippet will show a window titled "SFML works!" with a green circle: #include <SFML/Graphics.hpp> int main() { sf::RenderWindow window(sf::VideoMode(200, 200), "SFML works!"); sf::CircleShape shape(100.f...

As a developer, you frequently find yourself dealing with strings that are not created by your own code. These will often be supplied by third party libraries, external systems, or even end users. Validating strings of unclear provenance is considered to be one of the hallmarks of defensive program...

module.exports.routes = { 'GET /foo': 'FooController.index', 'GET /foo/new': 'FooController.new', 'POST /foo/create': 'FooController.create', 'GET /foo/:id/edit': 'FooController.edit', 'PUT /foo/:id/update': 'FooController.update', 'GET /foo/:id': 'FooController.show', ...

module.exports.routes = { '/foo': '/bar', 'GET /google': 'http://www.google.com' };

module.exports.routes = { // This function will be executed for all http verbs on all urls 'all /*', function (req, res, next) { // Expose the function `fooBar` to all views (via the locals object) res.locals.fooBar = function (arg1) { return 'foobar' + arg1; }; }, };...