Hi:
Does the following work?
xx <- matrix(1:5, nrow = 4, ncol = 10)
> colnames(xx) <- paste(rep(LETTERS[1:5], 2), rep(1:2, each = 5), sep = '')
> xx
A1 B1 C1 D1 E1 A2 B2 C2 D2 E2
[1,] 1 5 4 3 2 1 5 4 3 2
[2,] 2 1 5 4 3 2 1 5 4 3
[3,] 3 2 1 5 4 3 2 1 5 4
[4,] 4 3 2 1 5 4 3 2 1 5
# Reshape into a two-column matrix (20 x 2, filled columnwise) and
# take the row sums
> rowSums(matrix(xx, ncol = 2))
[1] 2 4 6 8 10 2 4 6 8 10 2 4 6 8 10 2 4 6 8 10
This of course assumes that the names in your columns are in
parallel subgroups (A*, B*, ..., E* in this toy example).
HTH,
Dennis
On Tue, May 11, 2010 at 5:36 PM, Q <quaga...@gmail.com> wrote:
>
> Hello,
>
> I am trying to figure out how to do a sum of items within a row. For
> example, I have a data frame something like this:
>
> A1 B1 ... A2 B2 ...
> 1 1 4 1 4
> 2 2 5 2 5
> 3 3 6 3 6
>
> What I want, is for each row, to get A1 + A2, B1 + B2, etc. which would,
> perhaps, give me a vector something like this c(2, 8, ... 4, 10 ... 6, 12).
>
> Does anyone know of a simple way to do this?
>
> Thanks a lot,
>
> Q
>
> --
> View this message in context:
> http://r.789695.n4.nabble.com/summing-items-within-a-row-tp2195458p2195458.html
> Sent from the R help mailing list archive at Nabble.com.
>
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