On Wed, 2008-02-20 at 13:39 -0800, Moshe Olshansky wrote:
> Try
>
> apply(A,2:3,sum)
If speed is an issue, then colSums is a faster version of the above:
> A <- array(c(1:27), dim = c(3,3,3))
> (res1 <- apply(A, 2:3, sum))
[,1] [,2] [,3]
[1,] 6 33 60
[2,] 15 42 69
[3,] 24 51 78
> (res2 <- colSums(A, dims = 1))
[,1] [,2] [,3]
[1,] 6 33 60
[2,] 15 42 69
[3,] 24 51 78
> all.equal(res1, res2)
[1] TRUE
This is only really an issue with large arrays or for use in repeated
calculations.
> system.time(replicate(10000, apply(A, 2:3, sum)))
user system elapsed
2.766 0.018 2.928
> system.time(replicate(10000, colSums(A, dims = 1)))
user system elapsed
0.563 0.006 0.596
HTH
G
>
> --- Saurav Pathak <[EMAIL PROTECTED]> wrote:
>
> > Hi,
> >
> > I cannot seem to figure out how to sum over an index
> > of a array.
> > For example, let A be a 3 dimensional array. I want
> > to, say, find
> > the sum over the first dimension. That is
> >
> > S_jk = Sum_i A_ijk
> >
> > where now S is a 2-dim matrix. I dont want to use a
> > loop.
> >
> > Thanks,
> > --
> > saurav
> >
> > ______________________________________________
> > R-help@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> > http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained,
> > reproducible code.
> >
>
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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