lodash/sampleSize.js

define(['./_baseClamp', './_baseRandom', './_isIterateeCall', './toArray', './toInteger'], function(baseClamp, baseRandom, isIterateeCall, toArray, toInteger) {

  /** Used as a safe reference for `undefined` in pre-ES5 environments. */
  var undefined;

  /**
   * Gets `n` random elements at unique keys from `collection` up to the
   * size of `collection`.
   *
   * @static
   * @memberOf _
   * @since 4.0.0
   * @category Collection
   * @param {Array|Object} collection The collection to sample.
   * @param {number} [n=1] The number of elements to sample.
   * @param- {Object} [guard] Enables use as an iteratee for methods like `_.map`.
   * @returns {Array} Returns the random elements.
   * @example
   *
   * _.sampleSize([1, 2, 3], 2);
   * // => [3, 1]
   *
   * _.sampleSize([1, 2, 3], 4);
   * // => [2, 3, 1]
   */
  function sampleSize(collection, n, guard) {
    var index = -1,
        result = toArray(collection),
        length = result.length,
        lastIndex = length - 1;

    if ((guard ? isIterateeCall(collection, n, guard) : n === undefined)) {
      n = 1;
    } else {
      n = baseClamp(toInteger(n), 0, length);
    }
    while (++index < n) {
      var rand = baseRandom(index, lastIndex),
          value = result[rand];

      result[rand] = result[index];
      result[index] = value;
    }
    result.length = n;
    return result;
  }

  return sampleSize;
});