Hi Jeff, David, what I'm trying to do is speed the currently used nest for loop
a<-matrix(c(1:6),ncol=3) b<-c(1,2,3,4) result<-matrix(rep(0, times=dim(a)[1]*length(b)),nrow=dim(a)[1]) for(ii in 1:dim(a)[1]){ for(jj in 1:length(b)){ result[ii,jj]<-a[ii,1]+a[ii,3]/b[jj] } } giving the result [,1] [,2] [,3] [1,] 1 3 5 [2,] 2 4 6 Thanks for taking a look. Cheers, Ingo ________________________________________ From: Jeff Newmiller [jdnew...@dcn.davis.ca.us] Sent: Wednesday, August 08, 2012 6:40 AM To: Ingo Reinhold; r-help@r-project.org Subject: Re: [R] Outer product from matrix by row and a vector Can you post what you want your answer to be for the a and b you have given already? --------------------------------------------------------------------------- Jeff Newmiller The ..... ..... Go Live... DCN:<jdnew...@dcn.davis.ca.us> Basics: ##.#. ##.#. Live Go... Live: OO#.. Dead: OO#.. Playing Research Engineer (Solar/Batteries O.O#. #.O#. with /Software/Embedded Controllers) .OO#. .OO#. rocks...1k --------------------------------------------------------------------------- Sent from my phone. Please excuse my brevity. Ingo Reinhold <in...@kth.se> wrote: >Dear all, > >I am facing a challenge when applying the outer product with a matrix >by rows. > >What I have is a rather big matrix, which I would like to convert into >a different matrix by doing something like > >outer(matrix_row, vector, function(x,y) x[1]+5*x[4]/y) > >In order to get there, I tried to get the matrix into a list using the >mefa package, as subsetting the original data appears too complicated. >However, if I apply the following code I always get a dimensional >error, as the unlist() function is applied to the whole list. > >library(mefa) >a<-matrix(c(1:6),ncol=3) >b<-c(1,2,3,4) >a<-mat2list(a,MARGIN=1) > >outer(a,b,function(x,y){unlist(a)[1]+unlist(a)[3]/b}) > > >Any idea how to do this more elegantly than a nested for-loop? > >Many thanks, > >Ingo > > [[alternative HTML version deleted]] > >______________________________________________ >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. ______________________________________________ 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.