Benchmark is probably a subset from a larger dataframe. R does not automatically remove empty levels but you can do it:
set.seed(42) dataset <- data.frame(Benchmark=factor(sample(LETTERS[1:26], 50, replace=TRUE), levels=LETTERS[1:26])) levels(dataset$Benchmark) # [1] "A" "B" "C" "D" "E" "F" "G" "H" "I" "J" "K" "L" "M" "N" "O" "P" "Q" "R" "S" # [20] "T" "U" "V" "W" "X" "Y" "Z" dataset$Benchmark <- factor(dataset$Benchmark) levels(dataset$Benchmark) # [1] "A" "C" "D" "F" "G" "H" "J" "K" "L" "M" "N" "O" "P" "Q" "R" "S" "T" "V" "X" # [20] "Y" "Z" There are times when you want to know if certain factor levels do not appear in a subset of the original data. ------------------------------------- David L Carlson Associate Professor of Anthropology Texas A&M University College Station, TX 77840-4352 ----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Borja Rivier Sent: Wednesday, July 24, 2013 8:25 AM To: r-help@r-project.org Subject: [R] Levels of a factor 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? Many thanks! Borja [[alternative HTML version deleted]] ______________________________________________ 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. ______________________________________________ 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.