R devel - Apr 2005 - Negative argument for head() and tail()

Dear R developers,

I'm a former APL programmer. In that language, the "take" (up
arrow) and
"drop" (down arrow) operators were extensively used to, well, take and
drop
elements of vectors. Functions head() and tail() are equivalents in R for the 
"take" operator, but nothing seems to mimic the "drop"
operator. I think it
would be useful.

For example, is there any simpler way to extract all elements of a vector but 
the last one than doing
> x[1:(length(x) - 1)]  ?
An equivalent of "drop" would make this easy.

Now, I think this could be easily implemented with the existing functions by 
allowing negative arguments to head() and tail(). For example, 
> head(x, -1)
would drop the first element of a vector and
> tail(x, -length(x))
the last one.

Is there any interest for such an extension?

I would be very willing to contribute a patch, although I don't have much 
experience in doing so.

Best regards,

-- 
  Vincent Goulet, Associate Professor
  ?cole d'actuariat
  Universit? Laval, Qu?bec 
  Vincent.Goulet@act.ulaval.ca   http://vgoulet.act.ulaval.ca

Le 20 Avril 2005 16:05, A.J. Rossini a ?crit?:
> x[-length(x)] ?
I feel idiot from that one, but hold on to my point. ;-)

Better example, then: how about a compact way to drop, say, the last 3 
elements of a vector? I think
> tail(x, -3)
would be nicer --- and more readable --- than
> x[-((length(x)-2):length(x))]
or
> x[0:3 -length(x)]
or some other convoluted way to achieve the same result.

(BTW, dropping the last element of a vector would be 'tail(x, -1)., not 
'tail(x, -length(x))' as stated in my original post. The latter would
drop
all the elements.)
> On 4/20/05, Vincent Goulet <vincent.goulet@act.ulaval.ca> wrote:
> > Dear R developers,
> >
> > I'm a former APL programmer. In that language, the
"take" (up arrow) and
> > "drop" (down arrow) operators were extensively used to,
well, take and
> > drop elements of vectors. Functions head() and tail() are equivalents
in
> > R for the "take" operator, but nothing seems to mimic the
"drop"
> > operator. I think it would be useful.
> >
> > For example, is there any simpler way to extract all elements of a
vector
> > but the last one than doing
> >
> > > x[1:(length(x) - 1)]  ?
> >
> > An equivalent of "drop" would make this easy.
> >
> > Now, I think this could be easily implemented with the existing
functions
> > by allowing negative arguments to head() and tail(). For example,
> >
> > > head(x, -1)
> >
> > would drop the first element of a vector and
> >
> > > tail(x, -length(x))
> >
> > the last one.
> >
> > Is there any interest for such an extension?
> >
> > I would be very willing to contribute a patch, although I don't
have much
> > experience in doing so.
> >
> > Best regards,
> >
> > --
> >   Vincent Goulet, Associate Professor
> >   ?cole d'actuariat
> >   Universit? Laval, Qu?bec
> >   Vincent.Goulet@act.ulaval.ca   http://vgoulet.act.ulaval.ca
> >
> > ______________________________________________
> > R-devel@stat.math.ethz.ch mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
-- 
  Vincent Goulet, Professeur agr?g?
  ?cole d'actuariat
  Universit? Laval, Qu?bec 
  Vincent.Goulet@act.ulaval.ca   http://vgoulet.act.ulaval.ca