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 <quagaars@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:
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>
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