On Thu, 24 Aug 2006, Martin Maechler wrote:
> >>>>> "Mitchell" == Mitchell Skinner <[EMAIL PROTECTED]>
> >>>>> on Thu, 24 Aug 2006 00:26:52 -0700 writes:
>
> Mitchell> I wrote:
> >> It still needs some debugging, to put it mildly
> >> (doesn't work properly on reals), but the basic idea appears to work.
>
> Mitchell> It works for reals on a 64-bit machine, but not on
> Mitchell> a 32-bit machine. I figure the culprit is this
> Mitchell> bit of c code:
>
>
> Mitchell> SET_VECTOR_ELT(wideCol, wideRow, VECTOR_ELT(longCol, rowNum));
>
>
> Mitchell> It seems like VECTOR_ELT and/or SET_VECTOR_ELT
> Mitchell> assumes that the vector elements are word-sized.
>
> No. It assumes that use what the C API calls 'VECTOR' and R users
> usually call list()s !!!
Since this is R-devel, it might be worth giving a fuller explanation (and
I had started writing one before seeing Martin's reply).
VECTOR_ELT is used for several types of SEXP, most commonly VECSXP (called
'list' at R level) but also EXPRSXP ('expression') and WEAKREFSXP ('weak
reference'), and can also be used for STRSXP ('character vector', but
STRING_ELT is better).
The R-devel version of R catches such user errors, so it is well be worth
using for code development.
> Do reread that part in the "Writing R Extensions" and rather
> look at REAL(.)[.] and REAL(.)[] = ..
And on the comment on wanting 'type-agnostic' C code: this is impossible
as C stores its types differently, and also note that REAL(.)[] is allowed
but VECTOR_ELT(x,i) = is not.
Another hint: if you find yourself writing REAL(.)[.] repeatedly, rewrite
it as
double *ra = REAL(a);
ra[i] = ...
since REAL(a) is a function call and can add appreciably to the execution
time if used inside a loop. (This is not true for internal code in R,
BTW, where REAL is a macro.)
And yes, I know there are examples like this in "Writing R Extensions" in
R 2.3.1, so this is another reason to use R-devel ....
--
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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