joint.all.js
function sample(collection, n, guard) {
      var length = collection ? collection.length : 0;
      if (typeof length != 'number') {
        collection = values(collection);
      }
      if (n == null || guard) {
        return collection ? collection[random(length - 1)] : undefined;
      }
      var result = shuffle(collection);
      result.length = nativeMin(nativeMax(0, n), result.length);
      return result;
    }
function sample(collection, n, guard) {
      var length = collection ? collection.length : 0;
      if (typeof length != 'number') {
        collection = values(collection);
      }
      if (n == null || guard) {
        return collection ? collection[random(length - 1)] : undefined;
      }
      var result = shuffle(collection);
      result.length = nativeMin(nativeMax(0, n), result.length);
      return result;
    }
Retrieves a random element or `n` random elements from a collection.

@static
@memberOf _
@category Collections
@param {Array|Object|string} collection The collection to sample.
@param {number} [n] The number of elements to sample.
@param- {Object} [guard] Allows working with functions, like `_.map`,
without using their `key` and `object` arguments as sources.
@returns {Array} Returns the random sample(s) of `collection`.
@example

_.sample([1, 2, 3, 4]);
// => 2

_.sample([1, 2, 3, 4], 2);
// => [3, 1]