Marc Schwartz <[EMAIL PROTECTED]> writes: > On Sat, 2006-10-21 at 21:04 -0400, Wensui Liu wrote: > > Dear Listers, > > > > I am wondering how to convert multiple dummy variables to 1 factor variable. > > > > Thanks. > > > > wensui > > I was thinking of a function that is essentially the reverse of > model.matrix() which is used by R modeling functions. I did not see one, > though it is possible that I missed it. > > However, I suppose that something along the lines of the following would > work. > > Say we have a matrix as follows, where the columns represent the > presence or absence of the factor levels, as one would see in a model > matrix. There should be a single '1' in each row as each row corresponds > to a single observation. > > > mat > Level1 Level2 Level3 Level4 Level5 > [1,] 0 1 0 0 0 > [2,] 1 0 0 0 0 > [3,] 0 0 0 1 0 > [4,] 0 0 1 0 0 > [5,] 0 0 0 0 1 > > > # Create a new factor based upon the index of each 1 in each row > # Use the matrix column names as the labels for each level > NewFactor <- factor(apply(mat, 1, function(x) which(x == 1)), > labels = colnames(mat)) > > > NewFactor > [1] Level2 Level1 Level4 Level3 Level5 > Levels: Level1 Level2 Level3 Level4 Level5
How about factor(mat%*%(1:5), labels = colnames(mat)) ? -- O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 ______________________________________________ [email protected] 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.
