[R] partial cumsum

[Carl Witthoft]

quote:
    > x <- c(1, 2, 3, NA, 5, 6, 7, 8, 9, 10)
    > rev(cumsum(rev(is.na(x))))
     [1] 1 1 1 1 0 0 0 0 0 0
A more natural way to do this is
    > cumsum(is.na(c(NA,x[-length(x)])))
     [1] 1 1 1 1 2 2 2 2 2 2
endquote

Both of which suggest the original problem could also be dealt with by 
using rle().  Something like

xna<-is.na(x)
rle(xna)
and then apply cumsum to sections of x based onthe lengths returned by rle

Carl