How to fill in the preceding numbers whenever there is a 0 in R?

Question

I have a string of numbers:

n1 = c(1, 1, 0, 6, 0, 0, 10, 10, 11, 12, 0, 0, 19, 23, 0, 0)

I need to replace 0 with the corresponding number righ

Answer 1

Because rle is the answer to everything:

#make an example including an NA value
n1 <- c(1, 1, 0, 6, NA, 0, 10, 10, 11, 12, 0, 0, 19, 23, 0, 0)
r <- rle(n1)
r$values[which(r$values==0)] <- r$values[which(r$values==0)-1]
inverse.rle(r)
# [1]  1  1  1  6 NA NA 10 10 11 12 12 12 19 23 23 23

A version that skips NAs would be:

n1 <- c(1, 1, 0, 6, NA, 0, 10, 10, 11, 12, 0, 0, 19, 23, 0, 0)
r <- rle(n1[!is.na(n1)])
r$values[which(r$values==0)] <- r$values[which(r$values==0)-1]
n1[!is.na(n1)] <- inverse.rle(r)
n1
# [1]  1  1  1  6 NA  6 10 10 11 12 12 12 19 23 23 23