scanIndexed()

Implementation Notes

Performs an ordered scan over the input stream, along with the index of the element being scanned/accumulated. This implementation attempts to behave like the non-indexing Gatherers::scan()in the JDK. For a folding version of this Gatherer, see foldIndexed().

Signature

scanIndexed(Supplier<OUTPUT> initialValue, IndexedAccumulatorFunction<OUTPUT, INPUT, OUTPUT> scanFunction)

• initialValue - A non-null Supplier to provide the seed value for the scan (this implementation does not assume the first element is the seed)
• scanFunction - IndexedAccumulatorFunction is a variation on a BiFunction which injects the int index of each element. This function does the actual scan/accumulation work.

Examples

Perform an indexed scan

This example joins the index and the input strings to show how this works.

Stream
    .of("A", "B", "C")
    .gather(
        Gatherers4j.scanIndexed(
            () -> "",
            (index, carry, next) -> carry + next + index
        )
    )
    .toList();

// [ "A0", "A0B1", "A0B1C2" ]