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

You could try this as well. This works nicely even if you want to include overlapping intervals, as controlled by by, and as a bonus, returns the intervals over which each value is derived:

library (gtools)
v2 <- running(v, fun=sum, width=3, align="left", allow.fewer=TRUE, by=3)

v2
1:3 4:6 7:8 
  6  15  15