Tutorial by Examples: r

It is possible to register a process (pid) to a global alias. This can be achieved with the build in register(Alias, Pid) function, where Alias is the atom to access the process as and Pid is the process id. The alias will be globally available! It is very easy to create shared state, wich is usu...

Each process in erlang has a process identifier (Pid) in this format <x.x.x>, x being a natural number. Below is an example of a Pid <0.1252.0> Pid can be used to send messages to the process using 'bang' (!), also Pid can be bounded to a variable, both are shown below MyProcessId =...

Subroutines hold code. Unless specified otherwise, they are globally defined. # Functions do not (have to) specify their argument list sub returns_one { # Functions return the value of the last expression by default # The return keyword here is unnecessary, but helps readability. return 1...

class Product(models.Model): name = models.CharField(max_length=20) price = models.FloatField() To Get average price of all products: >>> from django.db.models import Avg, Max, Min, Sum >>> Product.objects.all().aggregate(Avg('price')) # {'price__avg': 124.0} To ...

Subtracting the values of two pointers to an object results in a signed integer *1. So it would be printed using at least the d conversion specifier. To make sure there is a type being wide enough to hold such a "pointer-difference", since C99 <stddef.h> defines the type ptrdiff_t. ...

Most performance tips are very dependent of the current state of JS engines and are expected to be only relevant at a given time. The fundamental law of performance optimization is that you must first measure before trying to optimize, and measure again after a presumed optimization. To measure cod...

The package's official wiki has some essential materials: As a new user, you will want to check out the vignettes, FAQ and cheat sheet. Before asking a question -- here on StackOverflow or anywhere else -- please read the support page. For help on individual functions, the syntax is h...

Go to application/model File name - Home_model.php Inside the file class Home_model extends CI_Model { public $variable; public function __construct() { parent::__construct(); } public function get_data() { $query = $this->db->get('tabl...

public function method_name($single, $array) { echo $single; print_r($array); } Beware with the order which pass from controller to model.

Python makes it extremely intuitive to check if a string contains a given substring. Just use the in operator: >>> "foo" in "foo.baz.bar" True Note: testing an empty string will always result in True: >>> "" in "test" True

Javascript engines first look for variables within the local scope before extending their search to larger scopes. If the variable is an indexed value in an array, or an attribute in an associative array, it will first look for the parent array before it finds the contents. This has implications wh...

Open index.ios.js or index.android.js and delete everything between the <View> </View>. After that, write <Text> Hello World! </Text> and run the emulator. You should see Hello World! written on the screen! Congrats! You've successfully written your first Hello World!

ACID tables are supported since hive 0.14 version. Below table supports UPDATE/DELETE/INSERT Below configuration changes required in hive-site.xml. hive.support.concurrency = true hive.enforce.bucketing = true hive.exec.dynamic.partition.mode = nonstrict hive.txn.manager =org.apache.hadoop...

The CustomEvent API allows developers to create custom events and trigger them on DOM nodes, passing data along the way. event = new CustomEvent(typeArg, customEventInit); typeArg - DOMString representing the name of the event. customEventInit - is optional parameters (that will be passed as e ...

{-# LANGUAGE RecordWildCards #-} data Client = Client { firstName :: String , lastName :: String , clientID :: String } deriving (Show) printClientName :: Client -> IO () printClientName Client{..} = do p...

To copy a data.frame as a data.table, use as.data.table or data.table: DF = data.frame(x = letters[1:5], y = 1:5, z = (1:5) > 3) DT <- as.data.table(DF) # or DT <- data.table(DF) This is rarely necessary. One exception is when using built-in datasets like mtcars, which must be copi...

It is generally not considered 'best practice' to re-purpose the reserved names of Properties or Methods as the name(s) of your own procedures and variables. Bad Form - While the following is (strictly speaking) legal, working code the re-purposing of the Find method as well as the Row, Column and ...

Basic syntax DT[where, select|update|do, by] syntax is used to work with columns of a data.table. The "where" part is the i argument The "select|update|do" part is the j argument These two arguments are usually passed by position instead of by name. A sequence of steps c...

# example data DT <- data.table(Titanic) Suppose that, for each sex, we want the rows with the highest survival numbers: DT[Survived == "Yes", .SD[ N == max(N) ], by=Sex] # Class Sex Age Survived N # 1: Crew Male Adult Yes 192 # 2: 1st Female Adult Yes...

# example data DT = data.table(iris) DT[, Bin := cut(Sepal.Length, c(4,6,8))] Using .N .N in j stores the number of rows in a subset. When exploring data, .N is handy to... count rows in a group, DT[Species == "setosa", .N] # 50 or count rows in all groups, DT[, .N,...