[R] factor question

[Mark Difford]

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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> PLEASE do read the posting guide
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> 
> 

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