R devel - Nov 2007 - Returning vectors of two different data types back to R environment (from C).

Hello,

Quick question.

I have written a C function - I would like to make it return two vectors to
the R environment - one STRSXP vector, and one INTSXP vector.  Is this
possible/ easy to do using the API?

I looked, but could not find the answer to this  question in the "Writing R
Extensions" guide.

Thanks very much for your help!
Charles

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On Fri, 16 Nov 2007, Charles Danko wrote:
> Hello,
>
> Quick question.
>
> I have written a C function - I would like to make it return two vectors to
> the R environment - one STRSXP vector, and one INTSXP vector.  Is this
> possible/ easy to do using the API?
>
> I looked, but could not find the answer to this  question in the
"Writing R
> Extensions" guide.
Put them in a list? The SEXP function in the .Call() interface then 
returns a list wich you unpack on the R side. There are plenty of examples 
in the base code and in numerous contributed packages.
>
> Thanks very much for your help!
> Charles
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
-- 
Roger Bivand
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Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no

Charles Danko wrote:
> Hello,
> 
> Quick question.
> 
> I have written a C function - I would like to make it return two vectors to
> the R environment - one STRSXP vector, and one INTSXP vector.  Is this
> possible/ easy to do using the API?
> 
> I looked, but could not find the answer to this  question in the
"Writing R
> Extensions" guide.
  How does any R function return two different-typed values back to its 
caller? With a list - like list(foo=1,bar='baz'). Construct an R list in
your C code and return that... R Extensions should tell you how!

Barry

On Fri, Nov 16, 2007 at 03:49:09PM -0500, Charles Danko
wrote:
> Hello,
> 
> Quick question.
> 
> I have written a C function - I would like to make it return two vectors to
> the R environment - one STRSXP vector, and one INTSXP vector.  Is this
> possible/ easy to do using the API?
> 
> I looked, but could not find the answer to this  question in the
"Writing R
> Extensions" guide.
Yes, it's really quite reasonable to do, although it's not documented
in detail in the R-extensions manual.  As stated earlier, this will
only work with .Call and SEXP functions where you can handle R objects
within C.  

In Section 5.9 "Evaluating R expressions in C" it has an example using
lists in C.  Basically, lists are VECSXP objects so you can search for
that in R-exts.

Also, I would recommend looking at 5.7.6 "Handling lists" and the
function: 

SEXP getListElement(SEXP list, char *str)

You should look for that, and then grep the source files for
examples.  If you don't have grep to search the files, then I would
recommend the R gonzui site:

http://rgonzui.nakama.ne.jp/

Personally, I found the source code for det() to be a useful example,
you can search for that on R gonzui.

Good Luck

SEXP x,y,res;
PROTECT(res = allocVector(VECSXP, 2));
SET_VECTOR_ELT(res, 0, x = allocVector(REALSXP, 20)); 
SET_VECTOR_ELT(res, 1, y = allocVector(INTSXP, 10)); 
// code with x,y goes here

UNPROTECT(1);
return res;

On Fri, 2007-11-16 at 15:49 -0500, Charles Danko wrote:
> Hello,
> 
> Quick question.
> 
> I have written a C function - I would like to make it return two vectors to
> the R environment - one STRSXP vector, and one INTSXP vector.  Is this
> possible/ easy to do using the API?
> 
> I looked, but could not find the answer to this  question in the
"Writing R
> Extensions" guide.
> 
> Thanks very much for your help!
> Charles
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel