More elegant way to return a sequence of numbers based on booleans?

Question

Here\'s a sample of booleans I have as part of a data.frame:

atest <- c(FALSE, TRUE, TRUE, TRUE, TRUE, TRUE, TRUE, TRUE, TRUE, TRUE, FALSE, TRUE, TRUE,

Answer 1

Here is another approach using other familiar functions:

seq_along(atest) - cummax(seq_along(atest) * !atest) + 1L

Because it is all vectorized, it is noticeably faster than @Joshua's solution (if speed is of any concern):

f0 <- function(x) sequence(tabulate(cumsum(!x)))
f1 <- function(x) {i <- seq_along(x); i - cummax(i * !x) + 1L}
x  <- rep(atest, 10000)

library(microbenchmark)
microbenchmark(f0(x), f1(x))
# Unit: milliseconds
#   expr       min        lq    median        uq      max neval
#  f0(x) 19.386581 21.853194 24.511783 26.703705 57.20482   100
#  f1(x)  3.518581  3.976605  5.962534  7.763618 35.95388   100

identical(f0(x), f1(x))
# [1] TRUE