groupBy()

Turn a Stream<INPUT> into a Stream<List<INPUT>> where adjacent equal elements are in the same List and equality is measured by the given mappingFunction.

Implementation Notes

This function groups adjacent equal elements as measured by the provided mappingFunction, into lists. The lists returned from this Gatherer are unmodifiable. For the purposes of this gatherer, nulls are equal to each other but not equal to anything else.

For a version of groupBy() that measures equality with Object::equals(), see the group()Gatherer.

Signature

groupBy(Function<INPUT, Object> mappingFunction)

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

Examples

Group consecutive equal elements

Stream
    .of("A", "B", "C", "BB", "BBB", "C", "DD", "DD")
    .gather(Gatherers4j.groupBy(String::length))
    .toList();

// [ ["A", "B", "C"] ["BB"], ["C"], ["DD", "DD"] ]