reduce.js (1806B)
1 var arrayReduce = require('./_arrayReduce'), 2 baseEach = require('./_baseEach'), 3 baseIteratee = require('./_baseIteratee'), 4 baseReduce = require('./_baseReduce'), 5 isArray = require('./isArray'); 6 7 /** 8 * Reduces `collection` to a value which is the accumulated result of running 9 * each element in `collection` thru `iteratee`, where each successive 10 * invocation is supplied the return value of the previous. If `accumulator` 11 * is not given, the first element of `collection` is used as the initial 12 * value. The iteratee is invoked with four arguments: 13 * (accumulator, value, index|key, collection). 14 * 15 * Many lodash methods are guarded to work as iteratees for methods like 16 * `_.reduce`, `_.reduceRight`, and `_.transform`. 17 * 18 * The guarded methods are: 19 * `assign`, `defaults`, `defaultsDeep`, `includes`, `merge`, `orderBy`, 20 * and `sortBy` 21 * 22 * @static 23 * @memberOf _ 24 * @since 0.1.0 25 * @category Collection 26 * @param {Array|Object} collection The collection to iterate over. 27 * @param {Function} [iteratee=_.identity] The function invoked per iteration. 28 * @param {*} [accumulator] The initial value. 29 * @returns {*} Returns the accumulated value. 30 * @see _.reduceRight 31 * @example 32 * 33 * _.reduce([1, 2], function(sum, n) { 34 * return sum + n; 35 * }, 0); 36 * // => 3 37 * 38 * _.reduce({ 'a': 1, 'b': 2, 'c': 1 }, function(result, value, key) { 39 * (result[value] || (result[value] = [])).push(key); 40 * return result; 41 * }, {}); 42 * // => { '1': ['a', 'c'], '2': ['b'] } (iteration order is not guaranteed) 43 */ 44 function reduce(collection, iteratee, accumulator) { 45 var func = isArray(collection) ? arrayReduce : baseReduce, 46 initAccum = arguments.length < 3; 47 48 return func(collection, baseIteratee(iteratee, 4), accumulator, initAccum, baseEach); 49 } 50 51 module.exports = reduce;