Hi, Thank you all (Dimitris, Peter, Rolf, Gabor) for your suggestions. I tried with all your suggestions. I am getting different answers when I use:
rowsum(mat, gl(nrow(mat)/4, 4)) / 4 and m.new <- t(apply(array(t(m.old),dim=c(74,4,992/4)),c(1,3),mean)) When I tried with (assuming 'M' is my old matrix): dim(M) <- c(4,248,74) mn <- apply(M, c(2,3), mean) the following error occured: Error: dim<- : dims [product 73408] do not match the length of object [74] When I manually checked the answers, it seems that rowsum(mat, gl(nrow(mat)/4, 4)) / 4 gives me the correct answer. Thanks again for your time & suggestions. Regards, Ezhil --- Dimitris Rizopoulos <[EMAIL PROTECTED]> wrote: > yes you're right; it was my mistake. > > Best, > Dimitris > > ---- > Dimitris Rizopoulos > Ph.D. Student > Biostatistical Centre > School of Public Health > Catholic University of Leuven > > Address: Kapucijnenvoer 35, Leuven, Belgium > Tel: +32/(0)16/336899 > Fax: +32/(0)16/337015 > Web: http://med.kuleuven.be/biostat/ > > http://www.student.kuleuven.be/~m0390867/dimitris.htm > > > ----- Original Message ----- > From: "Rolf Turner" <[EMAIL PROTECTED]> > To: <[EMAIL PROTECTED]>; > <[EMAIL PROTECTED]> > Cc: <r-help@stat.math.ethz.ch> > Sent: Monday, May 29, 2006 1:55 PM > Subject: Re: [R] newbie question: ROW average > > > > Dimitris Rizopoulos wrote: > > > >> look at ?rowMeans; you can also use "apply(mat, > 1, mean)" but > >> rowMeans() is better. > > > > By my reading of the question, this is not what > > Ezhil wants. He said: > > > > ``I have a 992 x 74 matrix. I would like to form a > new matrix > > by averaging each 4 rows from the original > one.'' > > > > I.e. he wants (I think) the first row of the new > matrix > > to be the mean of the first 4 rows of the old one, > the > > second row of the new matrix to be the mean of > rows 5 > > through 8 of the old one, and so on. > > > > One way this could be done is via > > > > > m.new <- > t(apply(array(t(m.old),dim=c(74,4,992/4)),c(1,3),mean)) > > > > cheers, > > > > Rolf Turner > > [EMAIL PROTECTED] > > > > Disclaimer: > http://www.kuleuven.be/cwis/email_disclaimer.htm > > ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html