[Rd] Warnings generated by log2()/log10() are really large/takes a long time to display

[Prof Brian Ripley]

On Wed, 27 Feb 2008, Martin Maechler wrote:

> Thank you Henrik,
>
>>>>>> "HenrikB" == Henrik Bengtsson <hb at stat.berkeley.edu>
>>>>>>     on Tue, 26 Feb 2008 22:03:24 -0800 writes:
>
> {with many superfluous empty statements ( i.e., trailing ";" ):

Indeed!

>    HenrikB> x <- rnorm(1e6);
>
>    [................]
>
>
>    HenrikB> y <- log2(x);  # or log10(x)
>    HenrikB> w <- warnings();
>    HenrikB> print(object.size(w));
>    HenrikB> ## [1] 8000536
>    HenrikB> str(w);
>    HenrikB> ## List of 1
>    HenrikB> ##  $ NaNs produced: language log(c(2.12082478659910,
>    HenrikB> 1.40263187453398, 1.574125429
>    HenrikB> ## 83486, -0.816399069824751,  0.215940065840533, 1.20975177084379,
>    HenrikB> -0.340287874362
>    HenrikB> ## 813, 0.117151537611550,  ...
>    HenrikB> ##  - attr(*, "dots")= list()
>    HenrikB> ##  - attr(*, "class")= chr "warnings"
>
>    HenrikB> Note also how long it takes to display and str() the warning.
>
> Yes, indeed.
> It's a subtle problem and happens
> because in do_log1arg() a new call is constructed in which 'x'
> has already been evaluated.
>
> A subtle fix to the subtle problem
> is to replace  CAR(args) by CADR(call) in there
>
> --- arithmetic.c	(Revision 44626)
> +++ arithmetic.c	(working copy)
> @@ -1372,7 +1372,9 @@
>     if(PRIMVAL(op) == 10) tmp = ScalarReal(10.0);
>     if(PRIMVAL(op) == 2)  tmp = ScalarReal(2.0);
>
> -    PROTECT(Call = lang3(install("log"), CAR(args), tmp));
> +    /* CADR(call) instead of CAR(args), since 'args' have been
> +     * evaluated in Dispatch*(..) above : */
> +    PROTECT(Call = lang3(install("log"), CADR(call), tmp));
>     res = eval(Call, env);
>     UNPROTECT(1);
>     return res;
>
> -----
>
> That does fix the problem you've reported (and passes "make check")
> but I'm not quite at ease with it, since it will lead to
> effectively evaluate the argument *twice*.
>
> A different approach that I'd find cleaner
> would be to *not* construct and eval() a
> new Call inside do_log1arg, but I assume there had been a good
> reason for doing things they way they are now...

There was (although possibly no longer -- there was a bug in S4 dispatch 
of primitives that failed to re-promise args).

The real issue is somewhere else entirely, the complete deparse in 
print.warnings.

>
> Martin Maechler, ETH Zurich
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>

-- 
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