On Sat, 2007-12-08 at 19:26 -0800, Milton Cezar Ribeiro wrote: > Dear all, > > I have a data.frame with a factor collumn with about 10 levels. > After extract a subset of this data.frame, by selecting 2 of my 10 > levels, the new data.frame continue with original number of levels. > How can I adjust it in a manner that when I try levels(my.df) I > receive the actualyzed number of levels? > > By the way, I read my file using reab.table. > > I tryed solve it with : levels(my.df$my.var)<-unique(my.df$my.var) > but the problem remain. > > Many thanks, > > miltinho > Brazil
The default when subsetting factors (which happens when you subset a data frame) is to retain the original set of levels, even if they don't occur in the resultant subset. This is described in ?"[.factor" where the 'drop' argument is FALSE by default. To subset the factor and only retain levels for those values that are still present, you can use: MyFactor <- factor(MyFactor) or MyFactor <- MyFactor[, drop = TRUE] after subsetting the data frame. There is also a page in the R Wiki that describes some additional approaches: http://wiki.r-project.org/rwiki/doku.php?id=tips:data-manip:drop_unused_levels HTH, Marc Schwartz ______________________________________________ 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.
