Tutorial by Examples: r

It took me a while to get this right, so I decided to share a solution because it might save someone else several days of trial and error. The problem: I want to be able to enable/disable WCF tracing in my C# .NET application and choose the trace output filename. I don't want users editing the .con...

-- Create and drop a view in the current database. CREATE VIEW few_rows_from_t1 AS SELECT * FROM t1 LIMIT 10; DROP VIEW few_rows_from_t1; -- Create and drop a view referencing a table in a different database. CREATE VIEW table_from_other_db AS SELECT x FROM db1.foo WHERE x IS NOT NULL; DROP V...

let playerLayoutChangeListener = new android.view.View.OnLayoutChangeListener( { onLayoutChange : function ( v:View, left:number, top:number, right:number, bottom:number, oldLeft:number, oldTop:number, oldRight:number, oldBottom:number):any { if (left != oldLeft || top != oldTop ...

A computed column is computed from an expression that can use other columns in the same table. The expression can be a noncomputed column name, constant, function, and any combination of these connected by one or more operators. Create table with a computed column Create table NetProfit ( Sa...

You can overload a def if the signature is different: def printValue(x: Int) { println(s"My value is an integer equal to $x") } def printValue(x: String) { println(s"My value is a string equal to '$x'") } printValue(1) // prints "My value is an integer equal ...

Strings in Julia are delimited using the " symbol: julia> mystring = "Hello, World!" "Hello, World!" Note that unlike some other languages, the ' symbol cannot be used instead. ' defines a character literal; this is a Char data type and will only store a single Unico...

Multiple comparison operators used together are chained, as if connected via the && operator. This can be useful for readable and mathematically concise comparison chains, such as # same as 0 < i && i <= length(A) isinbounds(A, i) = 0 < i ≤ length(A) # same as Set...

We will look at how to implement custom comparisons by implementing a custom type, ordinal numbers. To simplify the implementation, we will focus on a small subset of these numbers: all ordinal numbers up to but not including ε₀. Our implementation is focused on simplicity, not speed; however, the i...

Julia supports a very large set of comparison operators. These include All of the following unicode sequences: > < >= ≥ <= ≤ == === ≡ != ≠ !== ≢ ∈ ∉ ∋ ∌ ⊆ ⊈ ⊂ ⊄ ⊊ ∝ ∊ ∍ ∥ ∦ ∷ ∺ ∻ ∽ ∾ ≁ ≃ ≄ ≅ ≆ ≇ ≈ ≉ ≊ ≋ ≌ ≍ ≎ ≐ ≑ ≒ ≓ ≔ ≕ ≖ ≗ ≘ ≙ ≚ ≛ ≜ ≝ ≞ ≟ ≣ ≦ ≧ ≨ ≩ ≪ ≫ ≬ ≭ ≮ ≯ ≰ ≱ ≲ ≳ ≴ ≵ ≶ ≷ ≸ ≹ ≺ ...

In languages such as C, the @goto statement is often used to ensure a function cleans up necessary resources, even in the event of an error. This is less important in Julia, because exceptions and try-finally blocks are often used instead. However, it is possible for Julia code to interface with C ...

Sometimes, one wants to run some initialization code once before testing a condition. In certain other languages, this kind of loop has special do-while syntax. However, this syntax can be replaced with a regular while loop and break statement, so Julia does not have specialized do-while syntax. Ins...

0.5.0 (Although this example is written using syntax introduced in version v0.5, it can work with few modifications on older versions also.) This implementation of breadth-first search (BFS) on a graph represented with adjacency lists uses while loops and the return statement. The task we will sol...

If you implement or create a listener in an Activity, always pay attention to the lifecycle of the object that has the listener registered. Consider an application where we have several different activities/fragments interested in when a user is logged in or out. One way of doing this would be to h...

% set mypath /home/tcluser/sources/tcl/myproject/test.tcl /home/tcluser/sources/tcl/myproject/test.tcl % set dir [file dirname $mypath] /home/tcluser/sources/tcl/myproject % set filename [file tail $mypath] test.tcl % set basefilename [file rootname $filename] test % set extension [file exte...

Consider the following code snippet: // Print the sum of the numbers 1 to 10 int count = 0; for (int i = 1; i < 010; i++) { // Mistake here .... count = count + i; } System.out.println("The sum of 1 to 10 is " + count); A Java beginner might be surprised to know that the...

context.globalCompositeOperation = 'source-atop' source-atop compositing clips new image inside an existing shape. // gold filled rect ctx.fillStyle='gold'; ctx.fillRect(100,100,100,75); // shadow ctx.shadowColor='black'; ctx.shadowBlur=10; // restrict new draw to cover existing pixels ct...

The javadoc for the Thread class shows two ways to define and use a thread: Using a custom thread class: class PrimeThread extends Thread { long minPrime; PrimeThread(long minPrime) { this.minPrime = minPrime; } public void run() { // compute primes l...

A lot of people who are new to multi-threading think that using threads automatically make an application go faster. In fact, it is a lot more complicated than that. But one thing that we can state with certainty is that for any computer there is a limit on the number of threads that can be run at ...

Returning a value One commonly used case: returning from main() #include <stdlib.h> /* for EXIT_xxx macros */ int main(int argc, char ** argv) { if (2 < argc) { return EXIT_FAILURE; /* The code expects one argument: leave immediately skipping t...

When programming in Prolog it is not always possible, or desirable, to create predicates which unify for every possible combination of parameters. For example, the predicate between(X,Y,Z) which expresses that Z is numerically between X and Y. It is easily implemented in the cases where X, Y, and Z ...