collection/shuffle.js

import baseRandom from '../internal/baseRandom';
import toIterable from '../internal/toIterable';

/**
 * Creates an array of shuffled values, using a version of the Fisher-Yates
 * shuffle. See [Wikipedia](https://en.wikipedia.org/wiki/Fisher-Yates_shuffle)
 * for more details.
 *
 * @static
 * @memberOf _
 * @category Collection
 * @param {Array|Object|string} collection The collection to shuffle.
 * @returns {Array} Returns the new shuffled array.
 * @example
 *
 * _.shuffle([1, 2, 3, 4]);
 * // => [4, 1, 3, 2]
 */
function shuffle(collection) {
  collection = toIterable(collection);

  var index = -1,
      length = collection.length,
      result = Array(length);

  while (++index < length) {
    var rand = baseRandom(0, index);
    if (index != rand) {
      result[index] = result[rand];
    }
    result[rand] = collection[index];
  }
  return result;
}

export default shuffle;