Function reduce

test-app/public/sinon.js:20304–20309

* Reduces `collection` to a value which is the accumulated result of running * each element in `collection` thru `iteratee`, where each successive * invocation is supplied the return value of the previous. If `accumulator` * is not given, the first element of `collection`

(collection, iteratee, accumulator)

         * // => { '1': ['a', 'c'], '2': ['b'] } (iteration order is not guaranteed)
         */
        function reduce(collection, iteratee, accumulator) {
          var func = isArray(collection) ? arrayReduce : baseReduce,
              initAccum = arguments.length < 3;
    
          return func(collection, getIteratee(iteratee, 4), accumulator, initAccum, baseEach);
        }
    
        /**
         * This method is like `_.reduce` except that it iterates over elements of