// Inspired by Underscore's groupBy:
// http://documentcloud.github.com/underscore/#groupBy

'use strict';

var callable = require('../../object/valid-callable')
  , value    = require('../../object/valid-value')

  , forEach = Array.prototype.forEach, apply = Function.prototype.apply;

module.exports = function (cb/*, thisArg*/) {
	var r;

	(value(this) && callable(cb));

	r = {};
	forEach.call(this, function (v) {
		var key = apply.call(cb, this, arguments);
		if (!r.hasOwnProperty(key)) r[key] = [];
		r[key].push(v);
	}, arguments[1]);
	return r;
};