Reduces a collection to a value which is the accumulated result of running each
element in the collection through the callback, where each successive callback execution
consumes the return value of the previous execution. If accumulator is not provided the
first element of the collection will be used as the initial accumulator value. The callback
is invoked with four arguments: (accumulator, value, index|key, collection).
Reduces a collection to a value which is the accumulated result of running each element in the collection through the callback, where each successive callback execution consumes the return value of the previous execution. If accumulator is not provided the first element of the collection will be used as the initial accumulator value. The callback is invoked with four arguments: (accumulator, value, index|key, collection).