• JS

const idx = x.map((item, i) => i);
while (y.length < k) {
  const i = parseInt(Math.random() * idx.length, 10);
  y.push(x[[idx[i]]]);
  idx.splice(i, 1);
}

• Clojure

(def y (->> x shuffle (take k)))

• C#

Random rnd = new Random();
List<int> y = x.OrderBy(r => rnd.Next()).Take(k).ToList();

• D

auto y = randomSample(x, k);

• Fortran

allocate (sample(k))
do i=1,k
   sample(i) = x(i)
end do
do i=k+1,n
  call random_number(a)
  j = 1 + int(i*a)
  if (j .le. k) sample(j) = x(i)
end do

• Go

y := make([]T, k)
perm := rand.Perm(len(x))
for i, v := range perm[:k] {
	y[i] = x[v]
}

• Haskell

randomSample :: Int -> [a] -> IO [a]
randomSample 0 x = pure []
randomSample k x = do
   i <- randomRIO (0, length x - 1)
   let (a, e:b) = splitAt i x
   l <- randomSample (k-1) (a ++ b)
   pure (e : l)

• Java

List<T> y = new ArrayList<>(x);
shuffle(y);
y = y.subList(0, k);

• PHP

$y = array_intersect_key($x, array_flip(array_rand($x, $k)));

• Pascal

function RandArr(Max: Integer): TIntegerDynArray;
var
  i, j, temp: Integer;
begin
  SetLength(Result, Max+1);
  for i := Low(Result) to High(Result) do Result[i] := i;
  i := Length(Result);
  while i > 0 do
  begin
    Dec(i);
    j := RandomRange(0,i);
    temp := Result[i];
    Result[i] := Result[j];
    Result[j] := temp;
  end;
end;
  
var
  Idx: TIntegerDynArray;
begin
  Idx := RandArr(High(X));
  SetLength(Y, k);
  for i := 0 to k-1 do Y[i] := X[Idx];
end.

• Perl

my @y = head $k, shuffle @x;

• Python

y = random.sample(x, k)

• Ruby

y = x.sample(k)

• Rust

let mut rng = &mut rand::thread_rng();
let y = x.choose_multiple(&mut rng, k).cloned().collect::<Vec<_>>();

• Smalltalk

y := x shuffled first: k.