Gatherers

fold

static fun <T : Any!, R : Any!> fold(
    initial: Supplier<R>!, 
    folder: BiFunction<in R, in T, out R>!
): Gatherer<T, *, R>!

Returns a Gatherer that performs an ordered, reduction-like, transformation for scenarios where no combiner-function can be implemented, or for reductions which are intrinsically order-dependent.

scan

static fun <T : Any!, R : Any!> scan(
    initial: Supplier<R>!, 
    scanner: BiFunction<in R, in T, out R>!
): Gatherer<T, *, R>!

Returns a Gatherer that performs a Prefix Scan -- an incremental accumulation -- using the provided functions. Starting with an initial value obtained from the Supplier, each subsequent value is obtained by applying the BiFunction to the current value and the next input element, after which the resulting value is produced downstream.

Example: {@snippet lang = java: * // will contain: ["1", "12", "123", "1234", "12345", "123456", "1234567", "12345678", "123456789"] * List numberStrings = * Stream.of(1,2,3,4,5,6,7,8,9) * .gather( * Gatherers.scan(() -> "", (string, number) -> string + number) * ) * .toList(); * }

windowFixed

static fun <TR : Any!> windowFixed(windowSize: Int): Gatherer<TR, *, MutableList<TR>!>!

Returns a Gatherer that gathers elements into windows -- encounter-ordered groups of elements -- of a fixed size. If the stream is empty then no window will be produced. The last window may contain fewer elements than the supplied window size.

Example: {@snippet lang = java: * // will contain: [[1, 2, 3], [4, 5, 6], [7, 8]] * List> windows = * Stream.of(1,2,3,4,5,6,7,8).gather(Gatherers.windowFixed(3)).toList(); * }

windowSliding

static fun <TR : Any!> windowSliding(windowSize: Int): Gatherer<TR, *, MutableList<TR>!>!

Returns a Gatherer that gathers elements into windows -- encounter-ordered groups of elements -- of a given size, where each subsequent window includes all elements of the previous window except for the least recent, and adds the next element in the stream. If the stream is empty then no window will be produced. If the size of the stream is smaller than the window size then only one window will be produced, containing all elements in the stream.

Example: {@snippet lang = java: * // will contain: [[1, 2], [2, 3], [3, 4], [4, 5], [5, 6], [6, 7], [7, 8]] * List> windows2 = * Stream.of(1,2,3,4,5,6,7,8).gather(Gatherers.windowSliding(2)).toList(); * * // will contain: [[1, 2, 3, 4, 5, 6], [2, 3, 4, 5, 6, 7], [3, 4, 5, 6, 7, 8]] * List> windows6 = * Stream.of(1,2,3,4,5,6,7,8).gather(Gatherers.windowSliding(6)).toList(); * }