Hi Barth, Use rowMeans() like this: mat <- matrix(rnorm(100), ncol=10) cbind(sum1.5 = rowSums(mat[,1:5]), sum2.6 = rowSums(mat[,2:6]))
Best, Ista On Thu, Mar 24, 2011 at 12:10 PM, Barth B. Riley <bbri...@chestnut.org> wrote: > Dear list > > I want to know if there is a function in R that enables one to create a new > matrix based on values in an existing matrix, whereby each column in the new > matrix is a row-specific summary (e.g., sum, mean) of multiple columns in the > original matrix. For instance, to take a 12-column matrix and collapse it > into a 3 column matrix containing the means for each row of columns 1-4, 5-8, > and 9-12 of the original matrix. I want to do this with a large number of > data matrices where the columns to collapse varies from dataset to dataset. > > Thanks > > Barth > > PRIVILEGED AND CONFIDENTIAL INFORMATION > This transmittal and any attachments may contain PRIVILEGED AND > CONFIDENTIAL information and is intended only for the use of the > addressee. If you are not the designated recipient, or an employee > or agent authorized to deliver such transmittals to the designated > recipient, you are hereby notified that any dissemination, > copying or publication of this transmittal is strictly prohibited. If > you have received this transmittal in error, please notify us > immediately by replying to the sender and delete this copy from your > system. You may also call us at (309) 827-6026 for assistance. > > ______________________________________________ > 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. > -- Ista Zahn Graduate student University of Rochester Department of Clinical and Social Psychology http://yourpsyche.org ______________________________________________ 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.
