How to copy a value in a vector to next position(s) in vector

Question

I have a vector that looks something like this:

c(0.5,0,0,0,0,0.7,0,0,0,0,0.4,0,0,0,0)

Suppose I want to copy the values on positions 1, 6

Answer 1

Here's one way:

zero.locf <- function(x) {
    if (x[1] == 0) stop('x[1] should not be 0')
    with(rle(x), {
        no.0 <- replace(values, values == 0, values[(values == 0) - 1])
        rep(no.0, lengths)
    })
}
x <- c(0.5,0,0,0,0,0.7,0,0,0,0,0.4,0,0,0,0)
zero.locf(x)
#  [1] 0.5 0.5 0.5 0.5 0.5 0.7 0.7 0.7 0.7 0.7 0.4 0.4 0.4 0.4 0.4

rle(x) returns a list with items values and lengths.

rle(x)
Run Length Encoding
  lengths: int [1:6] 1 4 1 4 1 4
  values : num [1:6] 0.5 0 0.7 0 0.4 0

with opens up this list and lets us reference these entries directly.