[R] levels update

[hadley wickham]

On Fri, Dec 5, 2008 at 6:50 AM, Antje <niederlein-rstat at yahoo.de> wrote:
> Hello,
>
> 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
>
> I guess, the solution is rather simple, but I cannot find it.

You might find it easier just to work with character vectors:

options(stringsAsFactors = FALSE)

Hadley

-- 
http://had.co.nz/