Applying function to consecutive subvectors of equal size

Question

I am looking for a nice and fast way of applying some arbitrary function which operates on vectors, such as sum, consecutively to a subvector of consecutive K e

Answer 1

Try this:

library(zoo)
rollapply(v, 3, by = 3, sum, partial = TRUE, align = "left")
## [1]  6 15 15

or

apply(matrix(c(v, rep(NA, 3 - length(v) %% 3)), 3), 2, sum, na.rm = TRUE)
## [1]  6 15 15

Also, in the case of sum the last one could be shortened to

colSums(matrix(c(v, rep(0, 3 - length(v) %% 3)), 3))