> 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")
> levels(my.sub$X1)
>
> # still gives me "a","b","c", though the subset does not contain entries
with
> "c" anymore
Two questions in one afternon; aren't I good to you!
levels(my.sub$X1[,drop=TRUE])
[1] "a" "b"
levels(factor(my.sub$X1))
[1] "a" "b"
Regards,
Richie.
Mathematical Sciences Unit
HSL
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