Calling R function from Rcpp

Question

I have a very basic question about C++ integration in R via Rcpp. Suppose I want to implement a simple function like this one in C++:

inte = function(x, y, a, b){
   model = approxfun(x, y)
   return(integrate(model, a, b)$value)
}

So a very basic approach would be to call R's function 'integrate' as much as needed:

// [[Rcpp::export]]
double intecxx(Function inte, NumericVector x, NumericVector y,
  double a, double b) {  
    NumericVector res;
    res = inte(x, y, a, b);
    return res[0];
}

However, I need to use this 'intecxx' in many other parts of my C++ code, so calling it from somewhere else results in 'inte' not being available in the scope. Any help is appreciated.

Answer 1

If you are willing to modify intecxx by hardcoding the call to inte inside the body, rather than trying to pass it as a parameter, you could use this approach:

#include <Rcpp.h>

/*** R
inte = function(x, y, a, b){
   model = approxfun(x, y)
   return(integrate(model, a, b)$value)
}

.x <- 1:10
set.seed(123)
.y <- rnorm(10)
*/

// [[Rcpp::export]]
double intecxx(Rcpp::NumericVector x, Rcpp::NumericVector y, double a, double b) {  
    Rcpp::NumericVector res;
    Rcpp::Environment G = Rcpp::Environment::global_env();
    Rcpp::Function inte = G["inte"];
    res = inte(x, y, a, b);
    return res[0];
}

I defined inte in the same source file as intecxx to ensure that it is available in the global environment, and therefore callable from within intecxx through G .

R> inte(.x, .y, 1, 10)
[1] 1.249325

R> intecxx(.x, .y, 1, 10)
[1] 1.249325

R> all.equal(inte(.x, .y, 1, 10),intecxx(.x, .y, 1, 10))
[1] TRUE