lodash/collection/reduce.js

define(['../internal/arrayReduce', '../internal/baseCallback', '../internal/baseEach', '../internal/baseReduce', '../lang/isArray'], function(arrayReduce, baseCallback, baseEach, baseReduce, isArray) {

  /**
   * Reduces `collection` to a value which is the accumulated result of running
   * each element in `collection` through `iteratee`, where each successive
   * invocation is supplied the return value of the previous. If `accumulator`
   * is not provided the first element of `collection` is used as the initial
   * value. The `iteratee` is bound to `thisArg`and invoked with four arguments;
   * (accumulator, value, index|key, collection).
   *
   * Many lodash methods are guarded to work as interatees for methods like
   * `_.reduce`, `_.reduceRight`, and `_.transform`.
   *
   * The guarded methods are:
   * `assign`, `defaults`, `merge`, and `sortAllBy`
   *
   * @static
   * @memberOf _
   * @alias foldl, inject
   * @category Collection
   * @param {Array|Object|string} collection The collection to iterate over.
   * @param {Function} [iteratee=_.identity] The function invoked per iteration.
   * @param {*} [accumulator] The initial value.
   * @param {*} [thisArg] The `this` binding of `iteratee`.
   * @returns {*} Returns the accumulated value.
   * @example
   *
   * _.reduce([1, 2], function(sum, n) {
   *   return sum + n;
   * });
   * // => 3
   *
   * _.reduce({ 'a': 1, 'b': 2 }, function(result, n, key) {
   *   result[key] = n * 3;
   *   return result;
   * }, {});
   * // => { 'a': 3, 'b': 6 } (iteration order is not guaranteed)
   */
  function reduce(collection, iteratee, accumulator, thisArg) {
    var func = isArray(collection) ? arrayReduce : baseReduce;
    return func(collection, baseCallback(iteratee, thisArg, 4), accumulator, arguments.length < 3, baseEach);
  }

  return reduce;
});