I don't think that this answers the poster's question, as he explicitly mentioned that some row and column indices could be missing.
I think it's simpler and much faster to do this by matrix indexing: mx <- matrix(NA,nr = max(foo[,1]),ncol = max(foo[,2])) ## fill with NA's mx[as.matrix(foo[,1:2])] <- foo[,3] See ?"[" for details. -- Bert Gunter -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of stephen sefick Sent: Wednesday, November 05, 2008 2:52 PM To: Philipp Pagel Cc: r-help@r-project.org Subject: Re: [R] Efficient way to fill a matrix #reshape package should do it library(reshape) foo <- data.frame(row=1:5, col=1:3, val=rnorm(15)) cast(foo, row~col) On Wed, Nov 5, 2008 at 5:47 PM, Philipp Pagel <[EMAIL PROTECTED]> wrote: > > Dear R experts, > > Suppose I have a data frame of three variables: > >> foo <- data.frame(row=1:5, col=1:3, val=rnorm(15)) >> foo > row col val > 1 1 1 -1.00631642 > 2 2 2 0.77715344 > 3 3 3 0.17358793 > 4 4 1 -1.67226988 > 5 5 2 1.08218836 > 6 1 3 1.32961329 > 7 2 1 -0.51186267 > 8 3 2 -1.20990127 > 9 4 3 -0.57786899 > 10 5 1 0.67102887 > 11 1 2 0.05646411 > 12 2 3 0.01146612 > 13 3 1 -3.12094409 > 14 4 2 -1.01932191 > 15 5 3 0.76736702 > > > I want to turn this into a matrix of val according to row and col. Let's also > assume that some combinations of row and col are missing - i.e. there will be > NAs in the resulting Matrix. My current approach is simple and works but is > slow for large datasets: > > mat <- matrix(nrow=max(foo$row), ncol=max(foo$col)) > for (line in 1:dim(foo)[1]) { > mat[foo[line, 'row'], foo[line, 'col']] <- foo[line, 'val'] > } > >> mat > [,1] [,2] [,3] > [1,] -1.0063164 0.05646411 1.32961329 > [2,] -0.5118627 0.77715344 0.01146612 > [3,] -3.1209441 -1.20990127 0.17358793 > [4,] -1.6722699 -1.01932191 -0.57786899 > [5,] 0.6710289 1.08218836 0.76736702 > > > Can anyone think of a more efficient way? > > cu > Philipp > > -- > Dr. Philipp Pagel > Lehrstuhl für Genomorientierte Bioinformatik > Technische Universität München > Wissenschaftszentrum Weihenstephan > 85350 Freising, Germany > http://mips.gsf.de/staff/pagel > > ______________________________________________ > 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. > -- Stephen Sefick Research Scientist Southeastern Natural Sciences Academy Let's not spend our time and resources thinking about things that are so little or so large that all they really do for us is puff us up and make us feel like gods. We are mammals, and have not exhausted the annoying little problems of being mammals. -K. Mullis ______________________________________________ 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.
