distinctBy()

Implementation Notes

This gatherer uses Object::equals() to measure equality of objects returned from the mappingFunction. Encounter order is preserved, so the first instance of a non-distinct element is the one that will be emitted to the output stream.

For a version of this function that measures distinctiveness based on Object::equals() alone, see the Stream::distinct()in the JDK. See also uniquelyOccurring() which emits elements that only exist once in the input stream.

Signature

distinctBy(Function<INPUT, Object> mappingFunction)

• mappingFunction - A non-null function to map INPUT types to an arbitrary Object to use for comparison

Examples

Filter objects distinctly by a specific property

record Person(String firstName, String lastName) {}

Stream
    .of(
        new Person("Todd", "Ginsberg"),
        new Person("Emma", "Ginsberg"),
        new Person("Todd", "Smith")
    )
    .gather(Gatherers4j.distinctBy(Person::firstName))
    .toList();

// [Person("Todd", "Ginsberg"), Person("Emma", "Ginsberg")]