var baseCallback = require('./baseCallback'), baseEach = require('./baseEach'), isArray = require('../lang/isArray'); /** * Creates a function that aggregates a collection, creating an accumulator * object composed from the results of running each element in the collection * through an iteratee. * * **Note:** This function is used to create `_.countBy`, `_.groupBy`, `_.indexBy`, * and `_.partition`. * * @private * @param {Function} setter The function to set keys and values of the accumulator object. * @param {Function} [initializer] The function to initialize the accumulator object. * @returns {Function} Returns the new aggregator function. */ function createAggregator(setter, initializer) { return function(collection, iteratee, thisArg) { var result = initializer ? initializer() : {}; iteratee = baseCallback(iteratee, thisArg, 3); if (isArray(collection)) { var index = -1, length = collection.length; while (++index < length) { var value = collection[index]; setter(result, value, iteratee(value, index, collection), collection); } } else { baseEach(collection, function(value, key, collection) { setter(result, value, iteratee(value, key, collection), collection); }); } return result; }; } module.exports = createAggregator;