Combine the elements of multiple sources into a source of sequences of value.

Source operators




Collects one element for every upstream and when all upstreams has emitted one element all of them are emitted downstream as a collection. The element order in the downstream collection will be the same order as the sources were listed.

Since the sources are provided as a list the individual types are lost and the downstream sequences will end up containing the closest supertype shared by all sourcesyou may have to make sure to have sources type casted to the same common supertype of all stream elements to use zipN.

See also:


In this sample we zip a stream of characters, a stream of numbers and a stream of colours. Into a single Source where each element is a VectorList of [character, number, color]:

sourceval chars = Source("a" :: "b" :: "c" :: "e" :: "f" :: Nil)
val numbers = Source(1 :: 2 :: 3 :: 4 :: 5 :: 6 :: Nil)
val colors = Source("red" :: "green" :: "blue" :: "yellow" :: "purple" :: Nil)

Source.zipN(chars :: numbers :: colors :: Nil).runForeach(println)
// prints:
// Vector(a, 1, red)
// Vector(b, 2, green)
// Vector(c, 3, blue)
// Vector(e, 4, yellow)
// Vector(f, 5, purple)
sourceSource<Object, NotUsed> chars = Source.from(Arrays.asList("a", "b", "c", "e", "f"));
Source<Object, NotUsed> numbers = Source.from(Arrays.asList(1, 2, 3, 4, 5, 6));
Source<Object, NotUsed> colors =
    Source.from(Arrays.asList("red", "green", "blue", "yellow", "purple"));

Source.zipN(Arrays.asList(chars, numbers, colors)).runForeach(System.out::println, system);
// prints:
// [a, 1, red]
// [b, 2, green]
// [c, 3, blue]
// [e, 4, yellow]
// [f, 5, purple]

Note how it stops as soon as any of the original sources reaches its end.

Reactive Streams semantics

emits when all of the inputs has an element available

completes when any upstream completes

backpressures all upstreams when downstream backpressures but also on an upstream that has emitted an element until all other upstreams has emitted elements

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