Dear Professor Brian Ripley,
please excuse my inability to interpret the help page correctly.
:[help(cbind)]
: For `cbind' (`rbind'), vectors of zero length are ignored unless
: the result would have zero rows (columns), for S compatibility.
I guess this implies that NULL is a zero length vector, even though
> is(NULL, "vector")
[1] FALSE
:[help(cbind)]
: (Zero-extent matrices do not occur in S and are not ignored in R.)
So, if neither NULL nor zero-extent matrices are ignored in R, I would
not expect the following results.
> cbind(NULL,diag(0,0,2))
[,1] [,2] [,3]
> cbind(diag(0,0,0),diag(0,0,2))
[,1] [,2]
Apparently, zero-extent matrices are ignored in R, or there is a
difference in the way of (not) ignoring zero-extent matrices and NULLs.
> So? It's a documented feature.
Yes, if you know how to interpret the documentation.
Sincerely
Johannes Martin
On Tue, 29 Jul 2003, Prof Brian Ripley wrote:
> That's as documented, on the help page. (NULL is a zero-length argument.)
> There's even a reason given.
>
> Exactly which part of the help page did you not understand?
>
> On Tue, 29 Jul 2003 [EMAIL PROTECTED] wrote:
>
> > R-Version: 1.7.1 (2003-06-16)
> > OS: Debian/GNU Linux
> >
> > cbind and rbind handle NULL parameters inconsistently.
> >
> > Consider:
> > > cbind()
> > NULL
> > > cbind(NULL)
> > NULL
> >
> > And:
> > > cbind(diag(x = 1, 1, 1))
> > [,1]
> > [1,] 1
> > > cbind(NULL, diag(x = 1, 1, 1))
> > [,1]
> > [1,] 1
> >
> > These seem to indicate that NULL parameters will be ignored in any call to
> > cbind and rbind. However:
> >
> > > cbind(NULL, diag(x = 1, 0, 1))
> > [,1] [,2]
> >
> > I.e. if one dimension of another parameter to cbind/rbind is zero,
> > cbind/rbind will create a row/column from the NULL parameter.
> >
> > This inconsistency creates problems in the construction of matrices within
> > loops and similar constructs.
>
> So? It's a documented feature.
>
> --
> 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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