Re: [R] blockwise sums

[Barry Rowlingson]

Liaw, Andy wrote:
If you insist, here's one way:
my.blockwisesum <- function(x, n, ...) {
    tapply(x, seq(1, length(x), by=n), sum, ...)
}
 Did you test that? I get:
> my.blockwisesum(1:10, 3)
Error in tapply(x, seq(1, length(x), by = n), sum, ...) :
        arguments must have same length
 Here's my solution with tapply and rep() to generate a vector like 
c(1,1,1,2,2,2,3,3,3,4):

baz.blockwisesum=
 function(v,n){tapply(v,rep(1:(1+length(v)/n),each=n)[1:length(v)],sum)}
> baz.blockwisesum(1:10,3)
 1  2  3  4
 6 15 24 10
 - just ignore the 1 to 4 names, they cant hurt you.
Baz
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