Vectorizing loop over vector elements

Question

I find it hard to come up with a fast solution to the following problem:

I have a vector of observations, which indicates the time of observation of certain phenomena. <

Answer 1

I suspect that your 0 values are actually NA values. Here I make them NA and than use na.locf (Last Observation Carried Forward) from package zoo:

example <- c(0,0,0,1,0,1,1,0,0,0,-1,0,0,-1,-1,0,0,1,0,0)
res <- example
#res[res==0] <- NA
#the same but faster
res <- res/res*res
library(zoo)
res <- na.locf(res,  na.rm = FALSE)
res[is.na(res)] <- 0
cbind(example, res)
#       example res
#  [1,]       0   0
#  [2,]       0   0
#  [3,]       0   0
#  [4,]       1   1
#  [5,]       0   1
#  [6,]       1   1
#  [7,]       1   1
#  [8,]       0   1
#  [9,]       0   1
# [10,]       0   1
# [11,]      -1  -1
# [12,]       0  -1
# [13,]       0  -1
# [14,]      -1  -1
# [15,]      -1  -1
# [16,]       0  -1
# [17,]       0  -1
# [18,]       1   1
# [19,]       0   1
# [20,]       0   1