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

As @Chase said in a comment, you can create your own grouping variable and then use that. Wrapping that process into a function would look like

myapply <- function(v, fun, group_size=1) {
    unname(tapply(v, (seq_along(v)-1) %/% group_size, fun))
}

which gives your results

> myapply(v, sum, group_size=3)
[1]  6 15 15

Note this does not require the length of v to be a multiple of the group_size.