[R] blockwise sums

[Liaw, Andy]

If you insist, here's one way:

my.blockwisesum <- function(x, n, ...) {
    tapply(x, seq(1, length(x), by=n), sum, ...)
}

Andy

> From: Lutz Prechelt
> 
> I am looking for a function like 
>   my.blockwisesum(vector, n)
> that computes sums of disjoint subsequences of length n from vector
> and can work with vector lengths that are not a multiple of n.
> 
> It should give me for instance
>   my.blockwisesum(1:10, 3) == c(6, 15, 24, 10)
> 
> Is there a builtin function that can do this?
> One could do it by coercing the vector into a matrix of width n,
> and then use apply,
> but that is cumbersome if the length is not divisible by n, 
> is it not?
> Any other ideas?
> 
>   Lutz
> 
> Prof. Dr. Lutz Prechelt;  prechelt at inf.fu-berlin.de
> Institut fuer Informatik; Freie Universitaet Berlin
> Takustr. 9; 14195 Berlin; Germany
> +49 30 838 75115; http://www.inf.fu-berlin.de/inst/ag-se/
> 
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