var baseAssignValue = require('./_baseAssignValue'),
      createAggregator = require('./_createAggregator');
  
  /** Used for built-in method references. */
  var objectProto = Object.prototype;
  
  /** Used to check objects for own properties. */
  var hasOwnProperty = objectProto.hasOwnProperty;
  
  /**
   * Creates an object composed of keys generated from the results of running
   * each element of `collection` thru `iteratee`. The order of grouped values
   * is determined by the order they occur in `collection`. The corresponding
   * value of each key is an array of elements responsible for generating the
   * key. The iteratee is invoked with one argument: (value).
   *
   * @static
   * @memberOf _
   * @since 0.1.0
   * @category Collection
   * @param {Array|Object} collection The collection to iterate over.
   * @param {Function} [iteratee=_.identity] The iteratee to transform keys.
   * @returns {Object} Returns the composed aggregate object.
   * @example
   *
   * _.groupBy([6.1, 4.2, 6.3], Math.floor);
   * // => { '4': [4.2], '6': [6.1, 6.3] }
   *
   * // The `_.property` iteratee shorthand.
   * _.groupBy(['one', 'two', 'three'], 'length');
   * // => { '3': ['one', 'two'], '5': ['three'] }
   */
  var groupBy = createAggregator(function(result, value, key) {
    if (hasOwnProperty.call(result, key)) {
      result[key].push(value);
    } else {
      baseAssignValue(result, key, [value]);
    }
  });
  
  module.exports = groupBy;