[R] summarize a vector

[Sam Steingold]

I have a long numeric vector v (length N) and I want create a shorter
vector of length N/k consisting of sums of k-subsequences of v:

v <- c(1,2,3,4,5,6,7,8,9,10)

N=10, k=3
===> [6,15,24,10]

I can, of course, iterate: 

> w <- vector(mode="numeric",length=ceiling(N/k))
> for (i in 1:length(w)) w[i] <- sum(v(i*k:(i+1)*k))

(modulo boundary conditions)
but I wonder if there is a better way.

thanks!

-- 
Sam Steingold (http://sds.podval.org/) on Ubuntu 12.04 (precise) X 11.0.11103000
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