R help - Apr 2006 - subsetting from C code, do_subset

Dear List,

do you know a way for subsetting an R object from C code? I would need the
equivalent of x[s]. I've found that the do_subset internal function does
this, but don't really know how to call it properly. I've two
SEXP's, one
for the object and one for the index. 

I'm thinking of creating an enviroment, place the two SEXP's in it and
then
just parse and run the corresponding R code, but there might be simpler
way... 

Any hints are appreciated. Thanks,
Gabor

-- 
Csardi Gabor <csardi at rmki.kfki.hu>    MTA RMKI, ELTE TTK

On Sat, 22 Apr 2006, Gabor Csardi wrote:
> Dear List,
>
> do you know a way for subsetting an R object from C code? I would need the
> equivalent of x[s]. I've found that the do_subset internal function
does
> this, but don't really know how to call it properly. I've two
SEXP's, one
> for the object and one for the index.
>
> I'm thinking of creating an enviroment, place the two SEXP's in it
and then
> just parse and run the corresponding R code, but there might be simpler
> way...
That's overkill.  You know where your objects are so you can set up a call 
with e.g. lang2 and eval it in the right place.  The code for e.g. optim 
might give you some ideas.

do_subset is not a public entry point, and may well not be visible to 
you in R >= 2.3.0.

[I'd say this was an R-devel question, BTW.]

-- 
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