[Rcpp-devel] RInside: C/C++ function(s) passed to R?
LEVRA-JUILLET William
william.levra-juillet at addactis.com
Wed Nov 13 09:31:47 CET 2019
Thx Sergei,
Yes you're right, I want to use my c++ function as a R function.
Sorry about the Banana function that takes 2 scalars, you’re right again, it should take a vector as input.
Please ignore this for now (this is a dummy example)
My c++ "Banana" function is already compiled in my project by the time I start he R session (via RInside).
I can pass it to R via a XPtr.
Something like R["myfuncptr"] = Rcpp::XPtr<func_type>(new func_type (Banana));
So, in R I got "myfuncptr" which is an "externalptr".
Now my only problem is to make that "externalptr" seen as a R function in R.
Maybe with something like a ".Call(externalptr, param...)"?
Here (https://stackoverflow.com/questions/13904786/r-pointer-to-c-function), Romains says something about wrapping the external pointer into an R function...
But I struggle to find the correct way to achieve this with the function parameters...
Thank you
William
-----Message d'origine-----
De : Serguei Sokol <serguei.sokol at gmail.com>
Envoyé : mardi 12 novembre 2019 17:49
À : LEVRA-JUILLET William <william.levra-juillet at addactis.com>; rcpp-devel at lists.r-forge.r-project.org
Objet : Re: [Rcpp-devel] RInside: C/C++ function(s) passed to R?
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-func
> tion-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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