grouped

Accumulate incoming events until the specified number of elements have been accumulated and then pass the collection of elements downstream.

Simple operators

Signature

Source.groupedSource.grouped Flow.groupedFlow.grouped

Description

Accumulate incoming events until the specified number of elements have been accumulated and then pass the collection of elements downstream.

Examples

The below example demonstrates how grouped groups the accumulated elements into Seq List and maps with other operation.

Scala
Source(1 to 7).grouped(3).runForeach(println)
// Vector(1, 2, 3)
// Vector(4, 5, 6)
// Vector(7)

Source(1 to 7).grouped(3).map(_.sum).runForeach(println)
// 6   (= 1 + 2 + 3)
// 15  (= 4 + 5 + 6)
// 7   (= 7)
Java
Source.from(Arrays.asList(1, 2, 3, 4, 5, 6, 7))
    .grouped(3)
    .runForeach(System.out::println, system);
// [1, 2, 3]
// [4, 5, 6]
// [7]

Source.from(Arrays.asList(1, 2, 3, 4, 5, 6, 7))
    .grouped(3)
    .map(g -> g.stream().reduce(0, Integer::sum))
    .runForeach(System.out::println, system);
// 6   (= 1 + 2 + 3)
// 15  (= 4 + 5 + 6)
// 7   (= 7)

Reactive Streams semantics

emits when the specified number of elements has been accumulated or upstream completed

backpressures when a group has been assembled and downstream backpressures

completes when upstream completes

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