filter

Filter the incoming elements using a predicate.

Simple operators

Signature

Source.filterSource.filter Flow.filterFlow.filter

Description

Filter the incoming elements using a predicate. If the predicate returns true the element is passed downstream, if it returns false the element is discarded.

See also filterNot.

Example

For example, given a Source of words we can select the longer words with the filter operator:

Scala

copysourceval words: Source[String, NotUsed] =
  Source(
    ("Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt " +
    "ut labore et dolore magna aliqua").split(" ").toList)

val longWords: Source[String, NotUsed] = words.filter(_.length > 6)

longWords.runForeach(println)
// consectetur
// adipiscing
// eiusmod
// incididunt

Java

copysourceSource<String, NotUsed> words =
    Source.from(
        Arrays.asList(
            ("Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt "
                    + "ut labore et dolore magna aliqua")
                .split(" ")));

Source<String, NotUsed> longWords = words.filter(w -> w.length() > 6);

longWords.runForeach(System.out::println, system);
// consectetur
// adipiscing
// eiusmod
// incididunt

Reactive Streams semantics

API docs

Flow.filterFlow.filter