From mtmorgan at fhcrc.org  Tue Jul 11 23:27:54 2006
From: mtmorgan at fhcrc.org (Martin Morgan)
Date: Tue, 11 Jul 2006 14:27:54 -0700
Subject: [Rd] often unnecessary duplicate in sapply / as.vector
In-Reply-To: <Pine.LNX.4.64.0607112018020.15720@gannet.stats.ox.ac.uk> (Brian
	Ripley's message of "Tue, 11 Jul 2006 20:32:38 +0100 (BST)")
References: <6phlkr5lhf7.fsf@gopher1.fhcrc.org>
	<Pine.LNX.4.64.0607071652450.9075@homer23.u.washington.edu>
	<Pine.LNX.4.64.0607111055000.12437@gannet.stats.ox.ac.uk>
	<Pine.LNX.4.64.0607112018020.15720@gannet.stats.ox.ac.uk>
Message-ID: <6phfyh7al2d.fsf@gopher1.fhcrc.org>

This is because RObjToCPtr is not quite careful enough with NAMED,
rather than an issue with as.XXX

tmp.c: void tmp(double *x) { x[0]=1; return; }

> f <- function(x) x
> x <- 0
> .C("tmp", f(x), DUP=FALSE)
[[1]]
[1] 1

> x
[1] 1

> x <- 0
> y <- x
> .C("tmp", x, DUP=FALSE)
[[1]]
[1] 1

> y
[1] 1

Martin

Prof Brian Ripley <ripley at stats.ox.ac.uk> writes:

> On Tue, 11 Jul 2006, Prof Brian Ripley wrote:
>
>> On Fri, 7 Jul 2006, Thomas Lumley wrote:
>
>> > On Fri, 7 Jul 2006, Martin Morgan wrote:
>
> [...]
>
>> > > More generally, perhaps as.vector might not duplicate when mode(x) == mode ?
>> > 
>> > This isn't a trivial change, because  mode(x)==mode does not guarantee 
>> > that as.vector(x, mode) has no effect.  For example, with mode="numeric" it 
>> > removes attributes.
>> 
>> And with mode="list" it does not (although that is not as documented).
>> We can certainly do better.  [This is another of those cases where 'mode' 
>> is confusing, and in fact it would be typeof(x) == mode.]
>
> Aargh: of course I should have guessed that quite a few people have 
> written code that assumes that e.g. as.double() duplicates.  The first I 
> came across is a .Fortran call in smooth.spline with DUP=FALSE which 
> despite all the warnings changes its 'w' argument and hence the return 
> result from smooth.spline if as.double is made more efficient.
>
> I really have no desire to spend any more time tracking down problems 
> caused by such rogue code, so I am going to leave this as is (with as.list 
> somewhat more efficient but the as.vector functions always duplicating).
>
> -- 
> Brian D. Ripley,                  ripley at stats.ox.ac.uk
> 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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[Rd] often unnecessary duplicate in sapply / as.vector
Martin Morgan