redundant factor levels after subsetting a dataset
On Nov 11, 2009, at 9:00 PM, Daniel Malter wrote:
#I have a data frame with a numeric and a character variable.
x=c(1,2,3,2,0,2,-1,-2,-4)
md=c(rep("Miller",3), rep("Richard",3),rep("Smith",3))
data1=data.frame(x,md)
#I subset this data.frame in a way such that one level of the
character
variable does not appear in the new dataset.
data2=data1[x>0,]
data3=subset(data1,x>0)
I thought this was asked and answered yesterday ((???)): > data2 <- as.data.frame(lapply(data2, function(x) x[,drop=TRUE])) > data2 x md 1 1 Miller 2 2 Miller 3 3 Miller 4 2 Richard 5 2 Richard > data3 <- as.data.frame(lapply(data3, function(x) x[,drop=TRUE])) > data3 x md 1 1 Miller 2 2 Miller 3 3 Miller 4 2 Richard 5 2 Richard > unique(data2$md) [1] Miller Richard Levels: Miller Richard > unique(data3$md) [1] Miller Richard Levels: Miller Richard
David > > #However, when I check the levels of the factor variable in the > subset data > frame, it still shows the levels that are now unused. > > unique(data2$md) > unique(data3$md) > > #This leads to complications in table and tapply that I want to avoid. > > table(data2$md) > tapply(data2$x,data2$md,mean) > > table(data3$md) > tapply(data3$x,data3$md,mean) > > #Basically, I want to completely remove "Smith" from data frame > data2 or > data3 so that it would not show up in table or tapply operations. > > Thanks for any pointers, > Daniel > > > > > > > > ----------------------------------------------- > "Who has visions, should see a doctor," > Helmut Schmidt, German Chancellor (1974-1982). > > ______________________________________________ > R-help at 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. David Winsemius, MD Heritage Laboratories West Hartford, CT