Pick random element

Pick random element is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

How does one pick a random element from a list?

Haskell

Creating a custom function:

<lang haskell>import Random (randomRIO)

pick :: [a] -> IO a pick xs = randomRIO (0, length xs - 1) >>= return . (xs !!)

x <- pick [1 2 3]</lang>

Using the random-extras library:

<lang haskell>import Data.Random import Data.Random.Source.DevRandom import Data.Random.Extras

x <- runRVar (choice [1 2 3]) DevRandom</lang>

Java

<lang java>import java.util.Random; ... int[] array = {1,2,3}; return array[new Random().nextInt(array.length)];</lang>

For a List object rather than an array, substitute list.get(...) for array[...]. If preserving the order of the List isn't important, you could call Collections.shuffle(list); and then list.get(0);. You would need to shuffle each time unless you removed the item from the list.

JavaScript

<lang javascript>var array = [1,2,3]; return array[Math.floor(Math.random() * array.length)];</lang>

PicoLisp

<lang PicoLisp>(get Lst (rand 1 (length Lst)))</lang>

Ruby

Works with: Ruby version 1.9

<lang ruby>irb(main):001:0> %w(north east south west).sample => "west" irb(main):002:0> (1..100).to_a.sample(2) => [17, 79]</lang>

Works with: Ruby version 1.8, but not 1.9

<lang ruby>irb(main):001:0> %w(north east south west).choice => "south"</lang>

Smalltalk

<lang smalltalk>x := #(1 2 3) atRandom.</lang>