[R] subset drop unused levels

[Peter Dalgaard]

Søren Merser <merser at image.dk> writes:

> hi there
> 
> tried to use subset with drop=TRUE, but all the 'old' levels are preserved,
> i.e. when calling e.g. ftable a lot of zeros are displayed
> 
> >x<-subset(LREG,  (kir=='AA' | kir=='BB') & (type=='t1' | otype=='t2'),
> drop=TRUE, select=c(event, kir, type))
> > ftable(x)
> 
> i explicit have to call factor like
> >ftable(event~factor(kir)+factor(type))
> 
> any hints?

Yes, the drop argument is misdocumented. It actually does the same as
the drop argument to [.data.frame. It was on this very list just
eleven days ago, see e.g. the below ref., including what to do if you
really want to get rid of unused levels

http://www.mail-archive.com/r-help@stat.math.ethz.ch/msg22459.html

(yet another interface to the archives...)

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
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