mapConcat

Transform each element into zero or more elements that are individually passed downstream.

Simple operators

Signature

Source.mapConcatSource.mapConcat Flow.mapConcatFlow.mapConcat

Description

Transform each element into zero or more elements that are individually passed downstream. This can be used to flatten collections into individual stream elements. Returning an empty iterable results in zero elements being passed downstream rather than the stream being cancelled.

See also statefulMapConcat, flatMapConcat, flatMapMerge

Example

The following takes a stream of integers and emits each element twice downstream.

Scala

copysourcedef duplicate(i: Int): List[Int] = List(i, i)

Source(1 to 3).mapConcat(i => duplicate(i)).runForeach(println)
// prints:
// 1
// 1
// 2
// 2
// 3
// 3

Java

copysourceIterable<Integer> duplicate(int i) {
  return Arrays.asList(i, i);
}

  Source.from(Arrays.asList(1, 2, 3))
      .mapConcat(i -> duplicate(i))
      .runForeach(System.out::println, system);
  // prints:
  // 1
  // 1
  // 2
  // 2
  // 3
  // 3

Reactive Streams semantics