[R] blockwise sums

[Peter Dalgaard]

Barry Rowlingson <B.Rowlingson at lancaster.ac.uk> writes:

> 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

Slight variant

pd.blockwisesum <- 
 function(v,n){N <- length(v); tapply(x,gl(ceiling(N/n), n, N), sum)}

> pd.blockwisesum(1:10,3)
 1  2  3  4
 6 15 24 10


-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907