[Rcpp-devel] RInside: C/C++ function(s) passed to R?

[Serguei Sokol]

Le 08/11/2019 à 11:06, LEVRA-JUILLET William a écrit :
> Hi all,
> 
> I’m evaluating RInside/Rcpp to interact our C++ project with R.
> 
> I’ve seen the samples to get/set data (matrix, dataframes, etc) to/from 
> R and it builds/works fine.
> 
> (Using gcc/mingw compiler from RTools on Windows)
> 
> My questions is about functions…
> 
> My project is C++, and it uses RInside to call R from our code.
> 
> Let’s say I have a C++ function implemented in my project, and I want to 
> pass that c++ function to R so it can be “used” as a R function 
> (typically passed as argument to optim/optimize)
> 
> I couldn’t find a way to do that using RInside.
> 
> Ideally, I’d like to achieve something like:
> 
> #include <RInside.h>
> 
> double Banana(double x, double y)
> 
> {
> 
> return (1-x)*(1-x)+100*(y-x*x)*(y-x*x);
> 
> }
> 
> Int main()
> 
> {
> 
> RInside R(argc,, argv);
> 
> R[“fn”] = Banana;
> 
> R.parseEval(“optim(c(-2,-2), fn”);
> 
> }
> 
> I believe it’s similar to 
> https://stackoverflow.com/questions/53729493/rinside-wrapping-a-c-function-for-use-in-an-r-function
> 
> But I can’t really understand the Rcpp::XPtr suggestion from Dirk.
> 
> Any help or pointers welcome J
Sorry for a late comment but for what it's worth, XPtr won't help here 
as optim() expects an R function, not C++ pointer to a function. 
Moreover, this R function takes only one argument -- a vector, not a 
couple of scalars. So maybe you meant something similar to:
#include <RInside.h>
int main(int argc, char *argv[]) {
    RInside R(argc, argv);
    R.parseEval("Rcpp::cppFunction('double Banana(double x, double y) 
{return (1-x)*(1-x)+100*(y-x*x)*(y-x*x);};', cacheDir='lib')");
    R.parseEval("fn <- function(p, ...) Banana(p[1L], p[2L])");
    Rcpp::RObject res = R.parseEval("optim(c(-2,-2), fn)");
    Rf_PrintValue(res);
    return 0;
}

which prints:

$par
[1] 0.9990277 0.9977136

$value
[1] 1.269722e-05

$counts
function gradient
      157       NA

$convergence
[1] 0

$message
NULL

As already underlined by others this is a sub-optimal way to use C++ 
functions in R but here it is imposed by optim() interface. For better 
designed interfaces (at least from "optimality of R/C++ exchanges" point 
of view) refer to examples cited by Dirk and Inaki.

Best,
Serguei.

> 
> Thx a mil
> 
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> 		
> 
> 
> *   William **LEVRA-JUILLET*
>     Senior Software Architect
> *   ADDACTIS Software*
>     +33 (0)4 81 92 13 00
> 
> 
> www.addactis.com 
> <https://addactis.letsignit.com/r/32/91871b88-8586-4561-b012-50a3a792527a/undefined>
> 
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> 
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> 
> 		
> 
> 
> *   William **LEVRA-JUILLET*
>     Senior Software Architect
> *   ADDACTIS Software*
>     +33 (0)4 81 92 13 00
> 
> 
> www.addactis.com 
> <https://addactis.letsignit.com/r/32/9cd210c2-e7cd-4d30-995a-e3ba4da16780/undefined>
> 
> 
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