foldIndexed()

Implementation Notes

Performs an ordered reduction over the input stream, along with the index of the element being reduced/folded. Because this implementation produces a single result, it is probably not suitable to apply to infinite input streams. This implementation attempts to behave like the non-indexing Gatherers::fold()in the JDK. For a scanning version of this Gatherer, see scanIndexed().

Signature

foldIndexed(Supplier<OUTPUT> initialValue, IndexedAccumulatorFunction<OUTPUT, INPUT, OUTPUT> foldFunction)

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

Examples

Perform an indexed fold

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

Stream
    .of("A", "B", "C", "D")
    .gather(
        Gatherers4j.foldIndexed(
            () -> "", // initialValue
            (index, carry, next) -> carry + String.format("%s%d ", next, index)
        )
     )
     .forEach(System.out::println);

// A0 B1 C2 D3