[Rd] Dealing with R list objects in C/C++
Wayne.Zhang at barclayscapital.com
Wayne.Zhang at barclayscapital.com
Thu Jan 27 22:03:11 CET 2011
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?
@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.
From: Martin Morgan [mailto:mtmorgan at fhcrc.org]
Sent: Wednesday, January 26, 2011 10:04 PM
To: Zhang, Wayne: IT (NYK)
Cc: r-devel at r-project.org
Subject: Re: [Rd] Dealing with R list objects in C/C++
On 01/26/2011 02:56 PM, Wayne.Zhang at barclayscapital.com wrote:
> 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) = 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)) = 1
or more succinctly
SET_VECTOR_ELT(arg, 0, ScalarInteger(1));
> REAL(arg) = 2.5; // control never reached here
and the second element
SET_VECTOR_ELT(arg, 1, ScalarReal(2.5));
> VECTOR_PTR(arg) = 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)) = 10.0; or with
less typing as
double *x = REAL(VECTOR_ETL(arg, 2));
x = 10.0; x = 11.0; x = 12.0; x = 13.0;
> REAL(VECTOR_PTR(arg)) = 10.0;
> REAL(VECTOR_PTR(arg)) = 11.0;
> REAL(VECTOR_PTR(arg)) = 12.0;
> REAL(VECTOR_PTR(arg)) = 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,
> I'll be grateful if you can point me to any online docs/samples.
> Thanks in advance,
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