That's not the purpose, though. MASS4 p.29 says
This implies all possible values for
the index. It is really only useful on the receiving side, where it
replaces the contents of the vector but keeps other aspects (the
class, the length, the names, \dots).
See also R-lang, which says
@strong{Empty}. The expression @code{x[]} returns @code{x}, but drops
``irrelevant'' attributes from the result. Only @code{names} and in
multi-dimensional arrays @code{dim} and @code{dimnames} attributes are
retained.
but does not (yet) cover what it calls `Subset assignment'.
On Mon, 28 Jun 2004, Spencer Graves wrote:
> "an assignment to a square bracket" implies that the object
> already exists and gives an error if it does not. Consider the following:
>
> > a[] <- 1:3
> Error: Object "a" not found
> > a <- 1:2
> > a[] <- 1:3
> Warning message:
> number of items to replace is not a multiple of replacement length
> >
>
> hope this helps. spencer graves
>
> [EMAIL PROTECTED] wrote:
>
> >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" <[EMAIL PROTECTED]>
> >To: "S�ren Merser" <[EMAIL PROTECTED]>
> >Cc: "R - help" <[EMAIL PROTECTED]>
> >Sent: Sunday, June 27, 2004 11:38 AM
> >Subject: Re: [R] subset drop unused levels
> >
> >
> >
> >
> >>S�ren Merser <[EMAIL PROTECTED]> 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/[EMAIL PROTECTED]/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
> >>~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907
> >>
> >>______________________________________________
> >>[EMAIL PROTECTED] mailing list
> >>https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> >>PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
> >>
> >>
> >>
> >
> >______________________________________________
> >[EMAIL PROTECTED] mailing list
> >https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> >PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
> >
> >
>
> ______________________________________________
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>
>
--
Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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