Tania Oh wrote: > Dear all, > > I used "which" to obtain a subset of values from my data.frame. > however, I find that there is a "trace" of the values I have removed. > Any suggestions would be greatly appreciate. > > Below is my data: > > d <- data.frame( val = 1:10, > group = sample(LETTERS[1:5], 10, repl=TRUE) ) > > >d > val group > 1 1 B > 2 2 E > 3 3 B > 4 4 C > 5 5 A > 6 6 B > 7 7 A > 8 8 E > 9 9 E > 10 10 A > > ## selecting everything that is not group "A" > d<-d[which(d$group !="A"),] > > > d > val group > 1 1 B > 2 2 E > 3 3 B > 4 4 C > 6 6 B > 8 8 E > 9 9 E > > > levels(d$group) > [1] "A" "B" "C" "E" > > ## why is group A still reflected here?
Because you have removed elements from a factor objects that has particular levels. You remove elements (=observations), but the factor still knows that all levels are possible (stired in attributes of the object). If you want to remove all levels without corresponding observations, use explicit drop=TRUE as the help page suggests, e.g.: d <- d[d$group != "A", ] d$group <- d$group[ , drop = TRUE] Uwe Ligges > Many thanks in advance, > tania > > D.phil student > Department of Physiology, Anatomy and Genetics > Oxford University > > ______________________________________________ > 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.
