Sink.reduce

Apply a reduction function on the incoming elements and pass the result to the next invocation.

Sink operators

Signature

Sink.reduceSink.reduce

Description

Apply a reduction function on the incoming elements and pass the result to the next invocation. The first invocation receives the two first elements of the flow.

Materializes into a Future CompletionStage that will be completed by the last result of the reduction function.

Example

Scala

copysourceval source = Source(1 to 10)
val result = source.runWith(Sink.reduce[Int]((a, b) => a + b))
result.map(println)(system.dispatcher)
// will print
// 55

Java

copysourceSource<Integer, NotUsed> ints = Source.from(Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10));
CompletionStage<Integer> sum = ints.runWith(Sink.reduce((a, b) -> a + b), system);
sum.thenAccept(System.out::println);
// 55

Reactive Streams semantics