R help - Jun 2004 - subset drop unused levels

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?

regards soren

S??ren 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 at 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
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907

thank you
sorry, but i missed that thread
your solution works (of cause)

hopefully the code and not the documentation will be corrected as the drop
argument comes very convenient or maybe as a new option:  drop.unused.levels=T
 
regards soren

btw 
how do i interpret an assigment to a square bracket?
d2[] <- lapply(d2, function(x) if (is.factor(x)) factor(x) else x) 


----- Original Message ----- 
From: "Peter Dalgaard" <p.dalgaard at biostat.ku.dk>
To: "S??ren Merser" <merser at image.dk>
Cc: "R - help" <r-help at stat.math.ethz.ch>
Sent: Sunday, June 27, 2004 11:38 AM
Subject: Re: [R] subset drop unused levels

> S??ren 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 at 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
> ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
> 
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