[R] subsetting from C code, do_subset

Prof Brian Ripley ripley at stats.ox.ac.uk
Sat Apr 22 20:33:56 CEST 2006

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

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