first of all, the subsetting line is overly complicated. dat.sub<-dat[dat$treat!='cont',]
will work just fine. R does exactly what you're describing. It knows the levels of the factor. Once you remove 'cont' from the data, that doesn't mean that the level is removed from the factor: > df<-data.frame(let=factor(sample(letters[1:5],100,replace=T)),num=rnorm(100)) > str(df) 'data.frame': 100 obs. of 2 variables: $ let: Factor w/ 5 levels "a","b","c","d",..: 1 5 1 4 3 5 2 2 1 3 ... $ num: num 0.224 -0.523 0.974 -0.268 -0.61 ... > df.sub<-df[df$let!='a',] > str(df.sub) 'data.frame': 82 obs. of 2 variables: $ let: Factor w/ 5 levels "a","b","c","d",..: 5 4 3 5 2 2 3 3 5 3 ... $ num: num -0.523 -0.268 -0.61 -1.383 -0.193 ... > unique(df.sub$let) [1] e d c b Levels: a b c d e > df.sub$let<-factor(df.sub$let) > unique(df.sub$let) [1] e d c b Levels: e d c b > str(df.sub$let) Factor w/ 4 levels "e","d","c","b": 1 2 3 1 4 4 3 3 1 3 ... > by redefining your factor you can eliminate the problem. the other option, if you don't want factors to begin with is: options(stringsAsFactors=FALSE) # to set the global option or dat<-read.csv("~/MyFiles/data.csv",stringsAsFactors=FALSE) # to set the option locally for this single read.csv call. On Tue, Nov 1, 2011 at 2:28 PM, Schreiber, Stefan <stefan.schrei...@ales.ualberta.ca> wrote: > Dear list, > > I cannot figure out why, after sub-setting my data, that particular item > which I don't want to plot is still in the newly created subset (please > see example below). R somehow remembers what was in the original data > set. A work around is exporting and importing the new subset. Then it's > all fine; but I don't like this idea and was wondering what am I missing > here? > > Thanks! > Stefan > > P.S. I am using R 2.13.2 for Mac. > >> dat<-read.csv("~/MyFiles/data.csv") >> class(dat$treat) > [1] "factor" >> dat > treat yield > 1 cont 98.7 > 2 cont 97.2 > 3 cont 96.1 > 4 cont 98.1 > 5 10 103.0 > 6 10 101.3 > 7 10 102.1 > 8 10 101.9 > 9 30 121.1 > 10 30 123.1 > 11 30 119.7 > 12 30 118.9 > 13 60 109.9 > 14 60 110.1 > 15 60 113.1 > 16 60 112.3 >> plot(dat$treat,dat$yield) >> dat.sub<-dat[which(dat$treat!='cont')] >> class(dat.sub$treat) > [1] "factor" >> dat.sub > treat yield > 5 10 103.0 > 6 10 101.3 > 7 10 102.1 > 8 10 101.9 > 9 30 121.1 > 10 30 123.1 > 11 30 119.7 > 12 30 118.9 > 13 60 109.9 > 14 60 110.1 > 15 60 113.1 > 16 60 112.3 >> plot(dat.sub$treat,dat.sub$yield) > > [[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.