[R] levels update

[Erich Neuwirth]

I do the following for a subsetted dataframe:

cleanfactors <- function(mydf){
  outdf<-mydf
  for (i in 1:dim(mydf)[2]){
    if (is.factor(mydf[,i]))
  outdf[,i]<-factor(mydf[,i])
  }
outdf
}


Antje 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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Erich Neuwirth, University of Vienna
Faculty of Computer Science
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