Excluding levels in table and xtabs
On Thu, 12 Dec 2002, Michael Friendly wrote:
Having looked over the replies and examined the code, I can't see any reason for table (and xtabs) to avoid honoring the exclude= argument for factors. There are often reasons for wanting to exclude certain levels, even non-missing in making a table. In my application, John Fox suggested that I could circumvent the problem by reading in the .csv file with na.strings="". However, it was only for making tables that I wanted to exclude the "" categories. The change to table() to have it honor the exclude option for factors is quite straight-forward. I wonder if the R team will consider placing this on its list. (revised version below)
It doesn't work for me (R1.6.1)
R> a<-factor( rep(c("A","B","C"),10))
R> a
[1] A B C A B C A B C A B C A B C A B C A B C A B C A B C A B C
Levels: A B C
mftable(a)
a A B C 10 10 10
mftable(a,exclude=c("A",NA))
a A B C 10 10 10 Warning message: NAs introduced by coercion and in addition it loses empty levels
levels(a)<-LETTERS[1:5] table(a)
a A B C D E 10 10 10 0 0
mftable(a)
a A B C 10 10 10 I agree that the fix needs to be done, though. -thomas