R help - Sep 2009 - Averaging rows if a condition is true.

Dear All,

I have matrix (50000 X 60) of subjects and their responses to a set of
questions. All responses are classified into categories (500). I would like to
average all subject's responses for each category. I wrote a code using a
for loop but is not working. Could please tell me what's wrong with the
code? I guess, there is a elegant R way of doing the same thing.

Thanks in advance.

Kind regards,
Ezhil


j <- 1; n <- dim(dat)[1]; cat <- as.character(dat[,1]);
row <- matrix(nrow=nrow(dat), ncol=ncol(dat));
for(i in 1:n-1) {
  if(cat[i] != cat[i+1]) {row[j, ] <- dat[j, ]}
  else {
      start <- j;
      end <- i;
      }
      row[j, ] <- colMeans(dat[j:i, ]);
      j+1;
  }

Hi,

Try to use aggregate function
RSiteSearch ("aggregate")   #for help


Regards
ML

A Ezhil a ?crit :
> Dear All,
>
> I have matrix (50000 X 60) of subjects and their responses to a set of
questions. All responses are classified into categories (500). I would like to
average all subject's responses for each category. I wrote a code using a
for loop but is not working. Could please tell me what's wrong with the
code? I guess, there is a elegant R way of doing the same thing.
>
> Thanks in advance.
>
> Kind regards,
> Ezhil
>
>
> j <- 1; n <- dim(dat)[1]; cat <- as.character(dat[,1]);
> row <- matrix(nrow=nrow(dat), ncol=ncol(dat));
> for(i in 1:n-1) {
>   if(cat[i] != cat[i+1]) {row[j, ] <- dat[j, ]}
>   else {
>       start <- j;
>       end <- i;
>       }
>       row[j, ] <- colMeans(dat[j:i, ]);
>       j+1;
>   }
>
> ______________________________________________
> 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.
>
>   

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Hi,

On Mon, Sep 7, 2009 at 11:46 AM, A Ezhil<ezhil02 at yahoo.com>
wrote:
> Dear All,
>
> I have matrix (50000 X 60) of subjects and their responses to a set of
questions. All responses are classified into categories (500). I would like to
average all subject's responses for each category. I wrote a code using a
for loop but is not working. Could please tell me what's wrong with the
code? I guess, there is a elegant R way of doing the same thing.
The dlply function in the plyr library provides a very easy and
intuitive way to do this ... if you're having problems using it,
please post a small representative matrix of your data that we can
paste into our own R session to slice and dice for you as an example.

-steve

-- 
Steve Lianoglou
Graduate Student: Computational Systems Biology
 | Memorial Sloan-Kettering Cancer Center
 | Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact