Tutorial by Examples: var

# example data DT = data.table(iris) DT[, Bin := cut(Sepal.Length, c(4,6,8))] To apply the same summarizing function to every column by group, we can use lapply and .SD DT[, lapply(.SD, median), by=.(Species, Bin)] # Species Bin Sepal.Length Sepal.Width Petal.Length Petal.Width # 1...

BAD CODE Dim f As System.Windows.Forms.Form f.ShowModal() GOOD CODE Dim f As System.Windows.Forms.Form = New System.Windows.Forms.Form ' Dim f As New System.Windows.Forms.Form ' alternative syntax f.ShowModal() EVEN BETTER CODE (Ensure proper disposal of IDisposable object more info) Us...

Local variables (unlike the other variable classes) do not have any prefix local_variable = "local" p local_variable # => local Its scope is dependent on where it has been declared, it can not be used outside the "declaration containers" scope. For example, if a local va...

Class variables have a class wide scope, they can be declared anywhere in the class. A variable will be considered a class variable when prefixed with @@ class Dinosaur @@classification = "Like a Reptile, but like a bird" def self.classification @@classification ...

Global variables have a global scope and hence, can be used everywhere. Their scope is not dependent on where they are defined. A variable will be considered global, when prefixed with a $ sign. $i_am_global = "omg" class Dinosaur def instance_method p "global vars ca...

Instance variables have an object wide scope, they can be declared anywhere in the object, however an instance variable declared on class level, will only be visible in the class object. A variable will be considered an instance variable when prefixed with @. Instance variables are used to set and g...

Reflection is useful when it is properly used for right purpose. By using reflection, you can access private variables and re-initialize final variables. Below is the code snippet, which is not recommended. import java.lang.reflect.*; public class ReflectionDemo{ public static void main(St...

// Obtain an instance of JavaScript engine ScriptEngineManager manager = new ScriptEngineManager(); ScriptEngine engine = manager.getEngineByName("nashorn"); try { // Set value in the global name space of the engine engine.put("name","Nashorn"); // E...

ScopedTypeVariables let you refer to universally quantified types inside of a declaration. To be more explicit: import Data.Monoid foo :: forall a b c. (Monoid b, Monoid c) => (a, b, c) -> (b, c) -> (a, b, c) foo (a, b, c) (b', c') = (a :: a, b'', c'') where (b'', c'') = (b <&g...

Environment variables that affect the go tool can be viewed via the go env [var ...] command: $ go env GOARCH="amd64" GOBIN="/home/yourname/bin" GOEXE="" GOHOSTARCH="amd64" GOHOSTOS="linux" GOOS="linux" GOPATH="/home/yourname&q...

Suggested max len First, I will mention some common strings that are always hex, or otherwise limited to ASCII. For these, you should specify CHARACTER SET ascii (latin1 is ok) so that it will not waste space: UUID CHAR(36) CHARACTER SET ascii -- or pack into BINARY(16) country_code CHAR(2) CHAR...

using System; using System.Threading; using System.Threading.Tasks; class Program { static void Main( string[] args ) { object sync = new object(); int sum = 0; Parallel.For( 1, 1000, ( i ) => { lock( sync ) sum = sum + i; // lock is necessa...

After defining an enum using any of the above ways and setting a variable, you can print both the variable's value as well as the corresponding name from the enum for the value. Here's an example: // Define the enum var ColorsEnum = { WHITE: 0, GRAY: 1, BLACK: 2 } Object.freeze(ColorsEnum); // D...

Passing Variable in URL as a method's parameter return $this->redirect([ 'controller' => 'users', 'action' => 'profile', $id ]); Url should be looks like this http://your_app_url/users/profile/{id} in UsersController.php file in profile() method class UsersController e...

You can also put custom variables in the front matter. These can be reused in the page layout. For example, if your front matter looks like this: --- layout: post title: "Using Custom Variables!" date: 2016-07-25 chicken: "I like Chicken." --- You can use the chicken va...

There are a number of predefined global variables that you can set in the front matter of a page or post. VariableDescriptionlayoutIf set, this specifies the layout file to use. Use the layout file name without the file extension. Layout files must be placed in the _layouts directory.permalinkIf y...

namespace CodeContractsDemo { using System; using System.Diagnostics.Contracts; public class Point { public int X { get; set; } public int Y { get; set; } public Point() { } public Point(int x, int y) { ...

Singleton classes share their instance/class variables with their object. class Example @@foo = :example end def Example.foo class_variable_get :@@foo end Example.foo #=> :example class Example def initialize @foo = 1 end def foo @foo end end e = Ex...

Let's say we have type ENUM('fish','mammal','bird') An alternative is type VARCHAR(20) COMENT "fish, bird, etc" This is quite open-ended in that new types are trivially added. Comparison, and whether better or worse than ENUM: (same) INSERT: simply provide the string (worse?)...

It is very easy to pass information between threads using the MVar a type and its accompanying functions in Control.Concurrent: newEmptyMVar :: IO (MVar a) -- creates a new MVar a newMVar :: a -> IO (MVar a) -- creates a new MVar with the given value takeMVar :: MVar a -> IO a -- retrieve...