R/merge_weighted.R

In tarakc02/lazylist: Lazily Evaluated Lists

#' Merge two streams so that the result is ordered
#'
#' The weight function is used to order the elements
#'
#' @param stream1 a lazy list
#' @param stream2 a lazy list
#' @param weight a function with one required argument
#' @export
merge_weighted <- function(stream1, stream2, weight) {
    if (is_emptystream(stream1)) return(stream2)
    if (is_emptystream(stream2)) return(stream1)

    s1car <- stream_car(stream1)
    s2car <- stream_car(stream2)

    if (weight(s1car) <= weight(s2car))
        return(cons_stream(s1car, merge_weighted(stream_cdr(stream1), stream2, weight)))

    if (weight(s1car) > weight(s2car))
        return(cons_stream(s2car, merge_weighted(stream1, stream_cdr(stream2), weight)))
}