cumulative sequence

cumseq.R

##' cumulative sequence of sequence changes.
##'
##' assigns a cumulative sum to a sequential occurrence in a vector.
##' 
##' @param x a vector containing sequences.
##' @return a vector containing change counts. 
##' @author phil
##' @examples
##'
##' my.seq                   <- c(6, 6, 6, 20, 20, 5, 3, 3, 3, 3, 6, 6)
##' stopifnot(cumseq(my.seq) == c(1, 1, 1, 2,  2,  3, 4, 4, 4, 4, 5, 5))
cumseq <- function(x) {
  rle.x <- rle(x)
  rle.x$values <- 1:length(rle.x$values)
  inverse.rle(rle.x)
}