Re: [Rd] PR#6614

From: Peter Dalgaard <p.dalgaard_at_biostat.ku.dk>
Date: Mon 27 Feb 2006 - 20:55:53 GMT

Bill Dunlap <bill@insightful.com> writes:

> On Wed, 23 Feb 2006, Peter Dalgaard wrote:
>
> > "Gabor Grothendieck" <ggrothendieck@gmail.com> writes:
> >
> > > Try this:
> > >
> > > subset(iris, select = - Species)
> >
> > Or, canonically,
> >
> > nm <- names(iris)
> > iris[, nm != "Species" ]
> >
> > iris[, -match("Species", nm)]
> >
> > >
> > > On 2/22/06, davidhughjones@gmail.com <davidhughjones@gmail.com> wrote:
> > > > I agree with the submitter that this needs some kind of solution.
> > > > Although data.frame[,-12] works, how do I drop a named column (the
> > > > most common use case)? (I found this bug while searching for an
> > > > answer.)
>
> That code with match only works if "Species" is actually
> a column of iris. If not, your result depends on whether
> you have a data.frame (an error) or a matrix (a column
> of NA's).
>
> I found some mail in a 15 year old sent-mail file that suggested
> allowing the tag 'except=' on any of the arguments to "[" to
> replace/extend the limited negative integer convention. The idea was
> that
> iris[ except=c(10:20), except=c("Petal.Width","Petal.Length")) ]
> would return all rows except 10:20 and all columns except
> the ones named.
> iris[ except=integer(0), ]
> would return all rows of iris, while iris[-integer(0), ] returns
> no rows of iris.
>
> This abuses the tag= notation, but the "[" function doesn't
> really support the i= and j= tags that some people expect.
>
> This would take care of the problem that subset(data.frame,select=-name)
> only lets you omit columns.
>
> The mail had a version of [.data.frame (for Splus 2.1?) that
> implemented this, although, if it is to be used it should be
> implemented in the most primitive [ code so all methods use it.

>From the language viewpoint, I think that using the same tag multiple times and mixing up tagged and positional argument matching would be quite nasty. I actually suspect that the argument matching rules will make it impossible in R (except possibly from C and .Primitive).

However, it could be possible to have an omit() function, as in

iris[ omit(c(10:20)), omit(c("Petal.Width","Petal.Length")) ]

all this needs to do is to tack an attribute onto the index which the indexing code can look for.

-- 
   O__  ---- Peter Dalgaard             ุster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)                  FAX: (+45) 35327907

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Received on Tue Feb 28 08:06:38 2006

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