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List:       r-devel
Subject:    Re: [Rd] Dealing with R list objects in C/C++
From:       Martin Morgan <mtmorgan () fhcrc ! org>
Date:       2011-01-27 21:16:51
Message-ID: 4D41E0C3.5070902 () fhcrc ! org
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On 1/27/2011 1:03 PM, Wayne.Zhang@barclayscapital.com wrote:
> Many thanks for the quick reply Martin, your code works as expected.  Next I'd like \
> to retrieve heterogeneous data from an SEXP object (let's just pretend it's the \
> same type as the one what I'm constructing).  I'm sure the relevant APIs are \
> defined in Rinternals.h, do we have API documentations for this header file \
> somewhere?
Hi Wayne -- Your best bet might be sections 5 and 6 of

     RShowDoc("R-exts")

or the books Dirk mentioned; see also Rdefines.h. Martin
> @Dirk: thanks for your help too.  I'm doing something very simple at the moment, so \
> I prefer not to bring in Rinside/Rcpp if possible. 
> Thanks again,
> Wayne
> 
> 
> -----Original Message-----
> From: Martin Morgan [mailto:mtmorgan@fhcrc.org]
> Sent: Wednesday, January 26, 2011 10:04 PM
> To: Zhang, Wayne: IT (NYK)
> Cc: r-devel@r-project.org
> Subject: Re: [Rd] Dealing with R list objects in C/C++
> 
> On 01/26/2011 02:56 PM, Wayne.Zhang@barclayscapital.com wrote:
> > Hi,
> > 
> > I'd like to construct an R list object in C++, fill it with relevant data, and \
> > pass it to an R function which will return a different list object back.  I have \
> > browsed through all the R manuals, and examples under tests/Embedding, but can't \
> > figure out the correct way.  Below is my code snippet: 
> > #include<Rinternals.h>
> > // Rf_initEmbeddedR and other setups already performed
> > 
> > SEXP arg, ret;
> > 
> > // this actually creates a pairlist.  I can't find any API that creates a list
> > PROTECT(arg = allocList(3));
> Allocate a list of length 3 via SEXPTYPE VECSXP
> 
> PROTECT(arg = allocVector(VECSXP, 3));
> 
> > // I want the first element to be type integer, second double, and third a \
> > vector. INTEGER(arg)[0]  = 1;            //<- runtime exception: "INTEGER() can \
> > only be applied to a 'integer', not a 'pairlist'
> set the first element of the list to an integer vector of length 1, and
> assign a value
> 
> SET_VECTOR_ELT(arg, 0, allocVector(INTSXP, 1));
> INTEGER(VECTOR_ELT(arg, 0))[0] = 1
> 
> or more succinctly
> 
> SET_VECTOR_ELT(arg, 0, ScalarInteger(1));
> 
> > REAL(arg)[1] = 2.5;               // control never reached here
> and the second element
> 
> SET_VECTOR_ELT(arg, 1, ScalarReal(2.5));
> 
> > VECTOR_PTR(arg)[2] = allocVector(REALSXP, 4);
> and for the third allocate a REALSXP and then fill
> 
> SET_VECTOR_ELT(arg, 2, allocVector(REALSXP, 4));
> 
> next lines should be ok as REAL(VECTOR_ELT(arg, 2))[0] = 10.0; or with
> less typing as
> 
> double *x = REAL(VECTOR_ETL(arg, 2));
> x[0] = 10.0; x[1] = 11.0; x[2] = 12.0; x[3] = 13.0;
> 
> > REAL(VECTOR_PTR(arg)[2])[0] = 10.0;
> > REAL(VECTOR_PTR(arg)[2])[1] = 11.0;
> > REAL(VECTOR_PTR(arg)[2])[2] = 12.0;
> > REAL(VECTOR_PTR(arg)[2])[3] = 13.0;
> > 
> > PROTECT(call = lang2(install(entryPoint.c_str()), arg));
> not sure where entryPoint.c_str() is coming from, but
> 
> PROTECT(call = lang2(install("fun"), arg));
> 
> with some debate about whether install("fun") should be PROTECT'ed.
> 
> > ret = R_tryEval(call, R_GlobalEnv,&errorOccurred);
> likely PROTECT(ret = ...) while checking errorOccurred, etc.
> 
> Hope that helps,
> 
> Martin
> 
> > 
> > I'll be grateful if you can point me to any online docs/samples.
> > 
> > Thanks in advance,
> > Wayne
> > 
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-- 
Dr. Martin Morgan, PhD
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N.
PO Box 19024 Seattle, WA 98109

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