The accumulator. Can also be referenced as $$
. Used to store the result of the lambda expression after each iteration of the reduce operation.
The accumulator parameter can be set to an intial value using the syntax acc = initValue
. In this case, the lambda expression is called with the first element of the input array. Then the result is set as the new accumulator value.
If an initial value for the accumulator is not set, the accumulator is set to the first element of the input array. Then the lamba expression is called with the second element of the input array.
The initial value of the accumulator and the lambda expression dictate the type of result produced by the reduce function. If the accumulator is set to acc = {}
, the result usually is of type Object. If the accumulator is set to acc = []
,
the result usually is of type Array. If the accumulator is set to acc = ""
, the result is usually be a String.