[R] levels update

Antje niederlein-rstat at yahoo.de
Fri Dec 5 13:50:52 CET 2008


I hope this question is not too stupid. I would like to know how to update 
levels after subsetting data from a data.frame.

df <- data.frame(factor(c("a","a","c","b","b")), c(4,5,6,7,8), c(9,1,2,3,4))
names(df) <- c("X1","X2","X3")

my.sub <- subset(df, X1 == "a" | X1 == "b")

# still gives me "a","b","c", though the subset does not contain entries with 
"c" anymore

I guess, the solution is rather simple, but I cannot find it.


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