Hi Edna,
Because I am "always" subsetting, I keep the following function handy
mydata[] <- lapply(mydata, function(x) if(is.factor(x)) x[,drop=T] else x)
This will strip out all factor levels that have been dropped by a previous
subsetting operation. For novice users of R (though I am not suggesting that
you are) it's priceless.
The original author, as far as I know, is Andy Liaw (author of the
randomForest package).
HTH, Mark.
Edna Bell wrote:
>
> Hi!
>
> Suppose I have a factor:
>
>> fac1 <- factor(rep(c("dog","cat","tree"),c(2,3,4)))
>> fac1
> [1] dog dog cat cat cat tree tree tree tree
> Levels: cat dog tree
>> length(fac1)
> [1] 9
>
> Now I want to get rid of the dogs:
>> fac1 <- fac1[3:9]
>> fac1
> [1] cat cat cat tree tree tree tree
> Levels: cat dog tree
>>
> How should I remove the dog from the level, please?
>
> Thanks in advance,
> Edna Bell
>
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