From: Jorge Ivan Velez <jorgeivanvelez_at_gmail.com>

Date: Wed, 21 May 2008 14:04:27 -0400

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. Received on Wed 21 May 2008 - 18:22:25 GMT

Date: Wed, 21 May 2008 14:04:27 -0400

Hi Gregory,

Try this:

cs=substr(colnames(Mat),1,1)

res=t(apply(t(Mat),2,tapply,cs,sum,na.rm=TRUE))
dim(res)

[1] 50 5

**HTH,
**
Jorge

On Wed, May 21, 2008 at 1:22 PM, Gregory Gentlemen < gregory_gentlemen_at_yahoo.ca> wrote:

> I am looking for an efficient way to solve the following problem. I have a

*> large matrix of continuous values with a small proportion of missing values.
**> Columns correspond to variables where each variable has two measurements,
**> call them A and B. The matrix is such that the columns are in sequence with
**> respect to the variables. I would like to sum up the two measurements for
**> each variable and each observation (the rows) for the whole matrix. Here is
**> an example of such a matrix with 5 variables (R, S, T, U, V) and 50
**> observations:
**>
**> set.seed(27)
**> Mat <- matrix(rnorm(500), nrow=50, ncol=10)
**> dimnames(Mat)[[2]] <-
**> c("R.A","R.B","S.A","S.B","T.A","T.B","U.A","U.B","V.A","V.B")
**>
**> miss.ind <- rbinom(500,1,prob=0.98)
**> Mat[!as.logical(miss.ind)] <- NA
**>
**> So I would like to produce 50 by 5 matrix where the columns are the sums of
**> A+B measurements for each of the 5 variables.
**>
**> Thanks for any help.
**>
**> Gregory Gentlemen
**>
**>
**> ---------------------------------
**>
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**>
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**>
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