R help - May 2010 - summing items within a row

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

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On May 11, 2010, at 8:36 PM, Q 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).
Addition of matrices with the "+" operator should give you a matrix  
which would have the corresponding sums. Because matrices are really  
vectors that are read in column order you might need to transpose  
before you read them out with c().

As always properly formed examples would be appreciated and the form  
of the appreciation would probably take the form of tested code.

-- 
David.
-- 
>
> 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.
>
> ______________________________________________
> R-help at 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.
David Winsemius, MD
West Hartford, CT

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:
>
http://r.789695.n4.nabble.com/summing-items-within-a-row-tp2195458p2195458.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> 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.
>
	[[alternative HTML version deleted]]

Thank you Dennis.  That was a great idea and it worked quite well!
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