From accumulated values to individual values in R

Question

sample1 <- c(9,9,24,24,27,27,39,45,54,54,54,57,57,57,57,66,66,69,75,81,90,102,105,108,120,120,123)

how can i make this to (9,0,15,0,3,0...) and so on? what this procedure called?

Answer 1

diff'll do it. (Note that you will need to prepend a 0 to 'pick up' the first step, from 0 to 9.)

diff(c(0, sample1))
#  [1]  9  0 15  0  3  0 12  6  9  0  0  3  0  0  0  9  0  3  6
# [20]  6  9 12  3  3 12  0  3