On Jul 24, 2013, at 11:35 AM, David Winsemius wrote: > > On Jul 24, 2013, at 6:25 AM, Borja Rivier wrote: > >> Hi all, >> >> I am having a bit of trouble using the levels() function. >> I have a factor with many elements, and when I use the function levels() to >> extract the list of unique elements, some of the elements returned are not >> actually in the factor. >> >> snipped > > When you take a subset of a factor vector, the levels are not reduced to the > unique values in the new vector. There is droplevels function that would need > to be applied if you already have such a vector, and there is a drop argument > that you need to set to TRUE in the `[.factors`
Make that `[.factor` > call if you want to "attack the problem at the source". > > ?`[.factor # missing trailing back-tick ?`[.factor` > ?droplevels > > -- David Winsemius Alameda, CA, USA ______________________________________________ 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.
