sample.js

var baseRandom = require('../internal/baseRandom'),
    isIterateeCall = require('../internal/isIterateeCall'),
    toArray = require('../lang/toArray'),
    toIterable = require('../internal/toIterable');

/* Native method references for those with the same name as other `lodash` methods. */
var nativeMin = Math.min;

/**
 * Gets a random element or `n` random elements from a collection.
 *
 * @static
 * @memberOf _
 * @category Collection
 * @param {Array|Object|string} collection The collection to sample.
 * @param {number} [n] The number of elements to sample.
 * @param- {Object} [guard] Enables use as a callback for functions like `_.map`.
 * @returns {*} Returns the random sample(s).
 * @example
 *
 * _.sample([1, 2, 3, 4]);
 * // => 2
 *
 * _.sample([1, 2, 3, 4], 2);
 * // => [3, 1]
 */
function sample(collection, n, guard) {
  if (guard ? isIterateeCall(collection, n, guard) : n == null) {
    collection = toIterable(collection);
    var length = collection.length;
    return length > 0 ? collection[baseRandom(0, length - 1)] : undefined;
  }
  var index = -1,
      result = toArray(collection),
      length = result.length,
      lastIndex = length - 1;

  n = nativeMin(n < 0 ? 0 : (+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;
}

module.exports = sample;