Transform a boost::array into NumericVector in Rcpp

Question

In my C++ script (run in R using Rcpp), I defined :

typedef boost::array< double ,3 > state_type;

Now, I want to create a function to tra

Answer 1

If you want to have seamless integration you will have to extend Rcpp::as(obj) and Rcpp::wrap(obj). How to do this is covered in the vignette Extending Rcpp. However, there is also an excellent entry in the Rcpp gallery that already covers a very similar case: Converting to and from boost::numeric::ublas::vector.

If you are content with only using state_type and not the general template, then you can use something like this:

#include 
// [[Rcpp::depends(BH)]]
#include 
typedef boost::array< double ,3 > state_type;

namespace Rcpp {
// non-intrusive extension via template specialisation
template <> state_type as(SEXP s);
// non-intrusive extension via template specialisation
template <> SEXP wrap(const state_type &s);
}

#include 

// define template specialisations for as and wrap
namespace Rcpp {
template <> state_type as(SEXP stsexp) {
  Rcpp::NumericVector st(stsexp);
  state_type result;
  if (st.size() != result.size()) Rcpp::stop("Incompatible length!");
  std::copy(st.begin(), st.end(), result.begin());
  return result;
}

template <> SEXP wrap(const state_type &st) {
  Rcpp::NumericVector result(st.size());
  std::copy(st.begin(), st.end(), result.begin());
  return Rcpp::wrap(result);
}
}

// make use of the new possibilities
// [[Rcpp::export]]
state_type alterStateType(state_type &st) {
  for (size_t i = 0; i < st.size(); ++i) {
    st[i] = i * st[i];
  }
  return st;
}

/*** R
alterStateType(1:3)
*/