@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:mtmor...@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.zh...@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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