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. > > For example I would have this: > >> vector <- dataset$Benchmark >> class(vector) > [1] "factor" >> length(vector) > [1] 35615 >> vector2 <- levels(vector) >> length(which(!(vector2 %in% vector))) > [1] 235 > > Does anyone know how this is possible? >
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` call if you want to "attack the problem at the source". ?`[.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.
