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Programming-Idioms

  • Ada
  • JS
  • C++

Idiom #11 Pick a random element from a list

The list x must be non-empty.

A hand picking a random note in a hat 
#include <random>
std::mt19937 gen;
std::uniform_int_distribution<size_t> uid (0, x.size () - 1);
x[uid (gen)];

Assuming that x.size () > 0
#include <random>
#include <algorithm>
std::ranges::sample(x, &result, 1, std::mt19937{std::random_device{}()});
with Ada.Numerics.Discrete_Random;
subtype Element_Type is Integer;
type List_Type is array (Positive range <>) of Element_Type;

function Pick_Random (X : List_Type) return Element_Type is
   subtype Index_Range  is Positive range X'Range;
   package Random_Index is new
     Ada.Numerics.Discrete_Random (Index_Range);
   Generator : Random_Index.Generator;
begin
   Random_Index.Reset (Generator);
   return X (Random_Index.Random (Generator));
end Pick_Random;
x[Math.floor(Math.random() * x.length)]

Note that Math.random is not cryptographically secure.
x[~~(Math.random() * x.length)];

~~ is a faster way to call Math.floor().

Note that Math.random is not cryptographically secure.
#include <stdlib.h>
x[rand() % x_length];

rand needs to be initialized by calling void srand(unsigned int);
New implementation...
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programming-idioms.org 
std::mt19937 gen;
std::uniform_int_distribution<size_t> uid (0, x.size () - 1);
x[uid (gen)];

std::ranges::sample(x, &result, 1, std::mt19937{std::random_device{}()});
subtype Element_Type is Integer;
type List_Type is array (Positive range <>) of Element_Type;

function Pick_Random (X : List_Type) return Element_Type is
   subtype Index_Range  is Positive range X'Range;
   package Random_Index is new
     Ada.Numerics.Discrete_Random (Index_Range);
   Generator : Random_Index.Generator;
begin
   Random_Index.Reset (Generator);
   return X (Random_Index.Random (Generator));
end Pick_Random;
x[Math.floor(Math.random() * x.length)]
x[~~(Math.random() * x.length)];
x[rand() % x_length];
(rand-nth x)
x[Random.Shared.Next(x.Count)]
x[new Random().Next(x.Count)]
x.randomSample(1);
x[new Random().nextInt(x.length)];
Enum.random(x)

lists:nth(rand:uniform(length(X)), X).
ktn_random:pick(X)
call random_number (a)
x(lbound(x) + int(a*ubound(x))

x[rand.Intn(len(x))]
func pick[T any](x []T) T {
	return x[rand.Intn(len(x))]
}
func pickT(x []T) T {
	return x[rand.Intn(len(x))]
}
x.shuffled().first()
(\l g -> l !! fst (randomR (0, length l) g))
(l !!) <$> randomRIO (0, length l - 1)
if (!x.isEmpty()) {
    Random r = new Random();
    T t = x.get(r.nextInt(x.size()));
}
x.get(ThreadLocalRandom.current().nextInt(0, x.size()))
x.get((int)(Math.random()*x.size()))
list.random()
(nth (random (length x)) x)
x[math.random(#x)]
x[arc4random_uniform(x.count)]
$x[ array_rand($x) ]
element := x.Items[random(x.count)];
element := x[random(length(x))];

my @x = ('a', 'list', 'of', 'random', 'items');
print $x[rand @x];
random.choice(x)
if x: z = choice(x)
x.sample
let mut rng = rand::thread_rng();
let choice = x.choose(&mut rng).unwrap();
x[rand::thread_rng().gen_range(0..x.len())]
val x = List(1, 2, 3, 4)
x.apply(Random.nextInt(x.size))
(list-ref x (random (length x)))
x atRandom
x(Random.Shared.Next(x.Count))
x(New Random().Next(x.Count))