Tutorial by Examples: x

Is "context.drawImage" not displaying the image on the Canvas?

Make sure your image object is fully loaded before you try to draw it on the canvas with context.drawImage. Otherwise the image will silently fail to display. In JavaScript, images are not loaded immediately. Instead, images are loaded asynchronously and during the time they take to load JavaScript...

html5-canvas • Images

Creating and executing a basic stored procedure

Using the Authors table in the Library Database CREATE PROCEDURE GetName ( @input_id INT = NULL, --Input parameter, id of the person, NULL default @name VARCHAR(128) = NULL --Input parameter, name of the person, NULL default ) AS BEGIN SELECT Name + ' is from ' + Country...

Microsoft SQL Server • Stored Procedures

Expanding a vector with the rep() function

The rep function can be used to repeat a vector in a fairly flexible manner. # repeat counting numbers, 1 through 5 twice rep(1:5, 2) [1] 1 2 3 4 5 1 2 3 4 5 # repeat vector with incomplete recycling rep(1:5, 2, length.out=7) [1] 1 2 3 4 5 1 2 The each argument is especially useful for ex...

R Language • Creating vectors

Pipelining and Multiplexing

var multiplexer = ConnectionMultiplexer.Connect("localhost"); IDatabase db = multiplexer.GetDatabase(); // intialize key with empty string await db.StringSetAsync("key", ""); // create transaction that utilize multiplexing and pipelining ITransaction transacton...

StackExchange.Redis • Pipelining

Reuse Multiplexer Across Application

class Program { private static Lazy<ConnectionMultiplexer> _multiplexer = new Lazy<ConnectionMultiplexer>( () => ConnectionMultiplexer.Connect("localhost"), LazyThreadSafetyMode.ExecutionAndPublication); static void Main(string[] args...

StackExchange.Redis • Getting started with StackExchange.Redis

Creating a Simple C# WinForms Application using a Text Editor

Open a text editor (like Notepad), and type the code below: using System; using System.ComponentModel; using System.Drawing; using System.Windows.Forms; namespace SampleApp { public class MainForm : Form { private Button btnHello; // The form's con...

winforms • Getting started with winforms

Doing extra scaling in pointer arithmetic

In pointer arithmetic, the integer to be added or subtracted to pointer is interpreted not as change of address but as number of elements to move. #include <stdio.h> int main(void) { int array[] = {1, 2, 3, 4, 5}; int *ptr = &array[0]; int *ptr2 = ptr + sizeof(int) * 2; ...

C Language • Common pitfalls

LOOP as an Expression

Unlike the loops in nearly every other programming language in use today, the LOOP in Common Lisp can be used as an expression: (let ((doubled (loop for x from 1 to 10 collect (* 2 x)))) doubled) ;; ==> (2 4 6 8 10 12 14 16 18 20) (loop for x from 1 to 10 sum x) ...

common-lisp • LOOP, a Common Lisp macro for iteration

Conditionally executing LOOP clauses

LOOP has its own IF statement that can control how the clauses are executed: (loop repeat 1000 for x = (random 100) if (evenp x) collect x into evens else collect x into odds finally (return (values evens odds))) Combining multiple clauses in an IF ...

common-lisp • LOOP, a Common Lisp macro for iteration

Coalesce basic Example

COALESCE() returns the first NON NULL value in a list of arguments. Suppose we had a table containing phone numbers, and cell phone numbers and wanted to return only one for each user. In order to only obtain one, we can get the first NON NULL value. DECLARE @Table TABLE (UserID int, PhoneNumber va...

Microsoft SQL Server • COALESCE

Creating a Simple VB.NET WinForms Application using a Text Editor

Open a text editor (like Notepad), and type the code below: Imports System.ComponentModel Imports System.Drawing Imports System.Windows.Forms Namespace SampleApp Public Class MainForm : Inherits Form Private btnHello As Button ' The form's constructor: thi...

winforms • Getting started with winforms

Cross Validation and Tuning with xgboost

library(caret) # for dummyVars library(RCurl) # download https data library(Metrics) # calculate errors library(xgboost) # model ############################################################################### # Load data from UCI Machine Learning Repository (http://archive.ics.uci.edu/ml/data...

R Language • xgboost

Convert Exceptions into Either or Option Types

To convert exceptions into Either or Option types, you can use methods that provided in scala.util.control.Exception import scala.util.control.Exception._ val plain = "71a" val optionInt: Option[Int] = catching(classOf[java.lang.NumberFormatException]) opt { plain.toInt } val eitherI...

Scala Language • Error Handling

Rebuild index

Over the course of time B-Tree indexes may become fragmented because of updating/deleting/inserting data. In SQLServer terminology we can have internal (index page which is half empty ) and external (logical page order doesn't correspond physical order). Rebuilding index is very similar to dropping...

SQL • Indexes

Finding the minimum or maximum element

If your array or array-like object is numeric, that is, if all its elements are numbers, then you can use Math.min.apply or Math.max.apply by passing null as the first argument, and your array as the second. var myArray = [1, 2, 3, 4]; Math.min.apply(null, myArray); // 1 Math.max.apply(null, my...

JavaScript • Arrays

Find max and min Element and Respective Index in a Vector

To find the largest or smallest element stored in a vector, you can use the methods std::max_element and std::min_element, respectively. These methods are defined in <algorithm> header. If several elements are equivalent to the greatest (smallest) element, the methods return the iterator to th...

C++ • std::vector