code: function transform(object, iteratee, accumulator) {
    var isArr = isArray_1(object),
        isArrLike = isArr || isBuffer_1(object) || isTypedArray_1(object);
  
    iteratee = _baseIteratee(iteratee, 4);
    if (accumulator == null) {
      var Ctor = object && object.constructor;
      if (isArrLike) {
        accumulator = isArr ? new Ctor : [];
      }
      else if (isObject_1(object)) {
        accumulator = isFunction_1(Ctor) ? _baseCreate(_getPrototype(object)) : {};
      }
      else {
        accumulator = {};
      }
    }
    (isArrLike ? _arrayEach : _baseForOwn)(object, function(value, index, object) {
      return iteratee(accumulator, value, index, object);
    });
    return accumulator;
  }
docs: An alternative to `_.reduce`; this method transforms `object` to a new
  `accumulator` object which is the result of running each of its own
  enumerable string keyed properties thru `iteratee`, with each invocation
  potentially mutating the `accumulator` object. If `accumulator` is not
  provided, a new object with the same `[[Prototype]]` will be used. The
  iteratee is invoked with four arguments: (accumulator, value, key, object).
  Iteratee functions may exit iteration early by explicitly returning `false`.
  
  @static
  @memberOf _
  @since 1.3.0
  @category Object
  @param {Object} object The object to iterate over.
  @param {Function} [iteratee=_.identity] The function invoked per iteration.
  @param {*} [accumulator] The custom accumulator value.
  @returns {*} Returns the accumulated value.
  @example
  
  _.transform([2, 3, 4], function(result, n) {
  result.push(n *= n);
  return n % 2 == 0;
  }, []);
  // => [4, 9]
  
  _.transform({ 'a': 1, 'b': 2, 'c': 1 }, function(result, value, key) {
  (result[value] || (result[value] = [])).push(key);
  }, {});
  // => { '1': ['a', 'c'], '2': ['b'] }