Thank you so much, Marc and Peter, Your method works great if I want to convert N dummies into N-level factor. But what if I want to convert N dummies into (N+1)-level factor? I tried both ways but none works.
Again, thank you so much! On 10/22/06, Marc Schwartz <[EMAIL PROTECTED]> wrote: > On Sun, 2006-10-22 at 09:35 +0200, Peter Dalgaard wrote: > > 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)) > > > > ? > > That'll do it too...and more efficiently of course. > > Thanks Peter. > > Regards, > > Marc > > ______________________________________________ > 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 > and provide commented, minimal, self-contained, reproducible code. > -- WenSui Liu (http://spaces.msn.com/statcompute/blog) Senior Decision Support Analyst Cincinnati Children Hospital Medical Center ______________________________________________ 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 and provide commented, minimal, self-contained, reproducible code.
