code: function createAggregator(setter, initializer) {
    return function(collection, iteratee) {
      var func = isArray_1(collection) ? _arrayAggregator : _baseAggregator,
          accumulator = initializer ? initializer() : {};
  
      return func(collection, setter, _baseIteratee(iteratee, 2), accumulator);
    };
  }
docs: Creates a function like `_.groupBy`.
  
  @private
  @param {Function} setter The function to set accumulator values.
  @param {Function} [initializer] The accumulator object initializer.
  @returns {Function} Returns the new aggregator function.