Dear Gang, this seem to solve your problem.
http://stackoverflow.com/questions/1195826/dropping-factor-levels-in-a-subsetted-data-frame-in-r best daniel ________________________________________ Feladó: r-help-boun...@r-project.org [r-help-boun...@r-project.org] ; meghatalmazó: Gang Chen [gangch...@gmail.com] Küldve: 2013. december 14. 21:09 To: r-help Tárgy: [R] Change factor levels Suppose I have a dataframe 'd' defined as L3 <- LETTERS[1:3] d0 <- data.frame(cbind(x = 1, y = 1:10), fac = sample(L3, 10, replace = TRUE)) (d <- d0[d0$fac %in% c('A', 'B'),]) x y fac 2 1 2 B 3 1 3 A 4 1 4 A 5 1 5 A 6 1 6 B 8 1 8 A Even though factor 'fac' in 'd' only has 2 levels, but it seems to bear the birthmark of 3 levels from its parent 'd0': str(d) 'data.frame': 6 obs. of 3 variables: $ x : num 1 1 1 1 1 1 $ y : num 2 3 4 5 6 8 $ fac: Factor w/ 3 levels "A","B","C": 2 1 1 1 2 1 How can I cut the umbilical cord so that factor 'fac' in 'd' would have an accurate birth certificate with the correct number of levels? Apparently the following does not work: levels(d$fac) <- c('A', 'B') Also any reason for this heritage? Thanks, Gang [[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.
