Tutorial by Examples: x

Convert a sparse matrix to a dense matrix using SciPy

from scipy.sparse import csr_matrix A = csr_matrix([[1,0,2],[0,3,0]]) >>>A <2x3 sparse matrix of type '<type 'numpy.int64'>' with 3 stored elements in Compressed Sparse Row format> >>> A.todense() matrix([[1, 0, 2], [0, 3, 0]]) >>&g...

scipy • Getting started with scipy

EXPLAIN Select query

An Explain infront of a select query shows you how the query will be executed. This way you to see if the query uses an index or if you could optimize your query by adding an index. Example query: explain select * from user join data on user.test = data.fk_user; Example result: id select_type...

SQL • EXPLAIN and DESCRIBE

Copy to clipboard from textarea using execCommand("copy")

Example: <!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title></title> </head> <body> <textarea id="content"></textarea> <input type="button" id="copy...

JavaScript • execCommand and contenteditable

Moving scroll when UITextView becomes first responder

Observe the notifications UIKeyboardWillShowNotification and UIKeyboardWillHideNotification, update the scrollView content insets according to keyboard height, then scroll to the focused control. - (void)viewDidLoad { [super viewDidLoad]; // register for keyboard notifications [[...

iOS • UITextField

Submitting Ajax form

View file: <?php use yii; use yii\bootstrap\ActiveForm; use yii\helpers\Html; ?> <?php $form = ActiveForm::begin([ 'action' => ['comments/ajax-comment'], 'options' => [ 'class' => 'comment-form' ] ]); ?> <?= $form->field($model, '...

yii2 • Ajax Request

box-sizing

The default box model (content-box) can be counter-intuitive, since the width / height for an element will not represent its actual width or height on screen as soon as you start adding padding and border styles to the element. The following example demonstrates this potential issue with content-...

CSS • The Box Model

Extracting a list of names from a list of Person(s)

Given a Person struct struct Person { let name: String let birthYear: Int? } and an Array of Person(s) let persons = [ Person(name: "Walter White", birthYear: 1959), Person(name: "Jesse Pinkman", birthYear: 1984), Person(name: "Skyler White&quo...

Swift Language • Functional Programming in Swift

Set up Retrofit and RxJava

Retrofit2 comes with support for multiple pluggable execution mechanisms, one of them is RxJava. To use retrofit with RxJava you first need to add the Retrofit RxJava adapter to your project: compile 'com.squareup.retrofit2:adapter-rxjava:2.1.0' then you need to add the adapter when building yo...

rx-java • Retrofit and RxJava

Using std::move to reduce complexity from O(n²) to O(n)

C++11 introduced core language and standard library support for moving an object. The idea is that when an object o is a temporary and one wants a logical copy, then its safe to just pilfer o's resources, such as a dynamically allocated buffer, leaving o logically empty but still destructible and co...

C++ • Move Semantics

Cross Site Scripting (XSS) protection

XSS attacks consist in injecting HTML (or JS) code in a page. See What is cross site scripting for more information. To prevent from this attack, by default, Django escapes strings passed through a template variable. Given the following context: context = { 'class_name': 'large" style=&...

Django • Security

Execute queries in the database when possible, not in memory.

Suppose we want to count how many counties are there in Texas: var counties = dbContext.States.Single(s => s.Code == "tx").Counties.Count(); The query is correct, but inefficient. States.Single(…) loads a state from the database. Next, Counties loads all 254 counties with all of the...

Entity Framework • Optimization Techniques in EF

Inserting TeX formulae in plots

TeX formulae can be inserted in the plot using the rc function import matplotlib.pyplot as plt plt.rc(usetex = True) or accessing the rcParams: import matplotlib.pyplot as plt params = {'tex.usetex': True} plt.rcParams.update(params) TeX uses the backslash \ for commands and symbols, whic...

matplotlib • Integration with TeX/LaTeX

Saving and exporting plots that use TeX

In order to include plots created with matplotlib in TeX documents, they should be saved as pdf or eps files. In this way, any text in the plot (including TeX formulae) is rendered as text in the final document. import matplotlib.pyplot as plt plt.rc(usetex=True) x = range(0, 10) y = [t**2 for t...

matplotlib • Integration with TeX/LaTeX

Localizing strings with gettext()

GNU gettext is an extension within PHP that must be included at the php.ini: extension=php_gettext.dll #Windows extension=gettext.so #Linux The gettext functions implement an NLS (Native Language Support) API which can be used to internationalize your PHP applications. Translating strings ...

PHP • Localization

Read Data from TextFile with Streams

I/O in node is asynchronous, so interacting with the disk and network involves passing callbacks to functions. You might be tempted to write code that serves up a file from disk like this: var http = require('http'); var fs = require('fs'); var server = http.createServer(function (req, res) { ...

Node.js • Using Streams

Changing contents of a text file

Example. It will be replacing the word email to a name in a text file index.txt with simple RegExp replace(/email/gim, 'name') var fs = require('fs'); fs.readFile('index.txt', 'utf-8', function(err, data) { if (err) throw err; var newValue = data.replace(/email/gim, 'name'); ...

Node.js • Filesystem I/O

Determining the line count of a text file

app.js const readline = require('readline'); const fs = require('fs'); var file = 'path.to.file'; var linesCount = 0; var rl = readline.createInterface({ input: fs.createReadStream(file), output: process.stdout, terminal: false }); rl.on('line', function (line) { linesCo...