round(numeric(0)) (PR#235)

[Prof Brian D Ripley]

On Thu, 29 Jul 1999, Kurt Hornik wrote:

> >>>>> ripley  writes:
> 
> > Try
> >> round(numeric(0))
> > [1] NA
> >> floor(numeric(0))
> > numeric(0)
> >> trunc(numeric(0))
> > numeric(0)
> 
> > S has them all as numeric(0), and I think R is wrong.
> > This looks like a design error in the math2 group: it applies to 
> > signif too, and also to the complex cases, e.g.
> >> signif(complex(0))
> > [1] NA
> 
> In math2, we have
> 
>     if (na < 1 || nb < 1) {
>         for (i = 0; i < n; i++)
>             y[i] = NA_REAL;
>     }
> 
> with
> 
>     na = LENGTH(sa);
>     nb = LENGTH(sb);
>     n = (na < nb) ? nb : na;
> 
> round(numeric(0)) really does round(numeric(0), 0) and hence we have na
> = 0, n = nb = 1.  I think math2 is about right because you need that
> sort of symmetry for recycling, but do_round() could know better.  Now
> 
> R> round(pi, 1:4)
> [1] 3.1000 3.1400 3.1420 3.1416
> 
> is supposed to work so is it really clear what we want?  (if either arg
> has length 0, does the result have length 0?  Should this be true for
> any math2 type function?)

Yes, I think that is what Svr4 says is the correct behaviour: the recycling
rules have been changed to be consistent (JMC says somewhere in the Green 
book) and any zero-length vector immediately makes the result of zero
length.


-- 
Brian D. Ripley,                  ripley@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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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