This is almost the "triplet representation" of sparse matrices, except the triplet representation excludes zero entries. If you have a lot of zeros, it would be worth a look at SparseM and Matrix.
Reid Huntsinger -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Liaw, Andy Sent: Tuesday, June 07, 2005 9:42 AM To: 'Stefan Mischke'; r-help@stat.math.ethz.ch Subject: RE: [R] transform large matrix into list Here's one way to do it: > M x1 x2 y1 1 2 y2 4 5 y3 7 8 > (L <- cbind(v=c(M), x=c(col(M)), y=c(row(M)))) v x y [1,] 1 1 1 [2,] 4 1 2 [3,] 7 1 3 [4,] 2 2 1 [5,] 5 2 2 [6,] 8 2 3 (The seemingly extraneous c()'s are to drop the dimensions of those matrices.) Are you sure your L[3, 3] is correct? Also, for a 10K^2 M, L is going to take up over 1.1GB of memory! You may want to look at SparseM and Matrix packages, which have facilities for handling sparse matrices. Andy > From: Stefan Mischke > > Dear List > > I need to transform a large matrix M with many NAs into a list L with > one row for each non missing cell. Every row should contain the cell > value in the first column, and its coordinates of the matrix > in column > 2 and 3. > > M: > x1 x2 > y1 1 2 > y2 4 5 > y3 7 8 > > L: > v x y > 1 1 1 > 4 1 2 > 7 1 2 > 2 2 1 > 5 2 2 > 8 2 3 > > I'm trying to do this with a loop, but since my matrix is quite large > (around 10k^2) this just takes a very long time. > There must be a more efficient and elegant way to do this. Any hints? > > Thanks, > Stefan > > ______________________________________________ > 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 > > > ______________________________________________ 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 ---------------------------------------------------------------------------- -- Notice: This e-mail message, together with any attachments,...{{dropped}} ______________________________________________ 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
