N random elements in array

OSCC · JavaScript, Array, Random · Oct 22, 2020

Gets n random elements at unique keys from an array up to the size of the array.

• Shuffle the array using the Fisher-Yates algorithm.
• Use Array.prototype.slice() to get the first n elements.
• Omit the second argument, n, to get only one element at random from the array.

const sampleSize = ([...arr], n = 1) => {
  let m = arr.length;
  while (m) {
    const i = Math.floor(Math.random() * m--);
    [arr[m], arr[i]] = [arr[i], arr[m]];
  }
  return arr.slice(0, n);
};

sampleSize([1, 2, 3], 2); // [3, 1]
sampleSize([1, 2, 3], 4); // [2, 3, 1]

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