On Fri, 5 Dec 2008, jim holtman wrote:
try this:
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$X1)
[1] "a" "b" "c"
my.sub$X1 <- factor(my.sub$X1)
I find
my.sub$X1 <- my.sub$X1[drop=TRUE]
a lot more self-explanatory. See ?"[.factor". However, if you find
yourself wanting to do this, ask why you have a factor (rather than a
character vector) in the first place.
levels(my.sub$X1)
[1] "a" "b"
On Fri, Dec 5, 2008 at 7:50 AM, Antje <[EMAIL PROTECTED]> 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.
Antje
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What is the problem that you are trying to solve?
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Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
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