Conversion of Rcpp::NumericMatrix to Eigen::MatrixXd

Question

I am facing a very similar issue to these questions:

I am writing an R-package, that uses the RcppEigen library for Matrix arithmetic. My problem is that the project is not compiling because of an error in the conversion of the Rcpp::NumericMatrix input to an Eigen::MatrixXd.

The file looks like this:

#include <map>
#include <Rcpp.h>
...
using namespace Eigen;
...
// [[Rcpp::export]]
Rcpp::List my_function(Rcpp::NumericMatrix input_matrix)
{
    ...
    Map<MatrixXd> GATE_matrixx(Rcpp::as<Map<MatrixXd> >(GATE_matrix));
    ...
}

This gives me the following error:

Myfile.cpp:40:65: required from here C:/Users/User/AppData/Local/Programs/R/R-4.2.2/library/Rcpp/include/Rcpp/internal/Exporter.h:31:31:error: matching function for call to 'Eigen::Map<Eigen::Matrix<double, -1, -1> >::Map(SEXPREC*&) 31 | Exporter( SEXP x ) : t(x) | ^ In file included from C:/Users/User/AppData/Local/Programs/R/R-4.2.2/library/RcppEigen/include/Eigen/Core:19 from C:/Users/User/AppData/Local/Programs/R/R-4.2.2/library/RcppEigen/include/Eigen/SparseCore:11 from C:/Users/User/AppData/Local/Programs/R/R-4.2.2/library/RcppEigen/include/Eigen/Sparse:26 from Myfile.cpp:8

I have also tried to change the line to:

MatrixXd input_matrix_eigen(Rcpp::as\<MatrixXd\>(input_matrix));

This gives me the equivalent error :

Myfile.cpp:40:54: required from here C:/Users/User/AppData/Local/Programs/R/R 4.2.2/library/RcppEigen/include/Eigen/src/Core/Matrix.h:332:31:error: matching function for call to 'Eigen::Matrix<double, -1, -1>::_init1<SEXPREC*>(SEXPREC* const&)

Do you have any ideas? If more information is required to evaluate the issue, just let me know.

Welcome to StackOverflow! The documentation (and the unit tests) of package RcppEigen has many examples of how to use it, including with matrices as input or result. As do many of the nearly four hundred CRAN packages using RcppEigen. — Dirk Eddelbuettel, Feb 02 '23 at 12:55
You example is not fully complete and reproducible but one issue is the likely lack of `#include `. — Dirk Eddelbuettel, Feb 02 '23 at 13:03

score 0 · Answer 1 · answered Feb 02 '23 at 13:02

If you use the command

RcppEigen::RcppEigen.package.skeleton("demoPackage")

an example package demoPackage is created for you which you can install the usual way. It contains example functions to create amd return a matrix:

// [[Rcpp::export]]
Eigen::MatrixXd rcppeigen_hello_world() {
    Eigen::MatrixXd m1 = Eigen::MatrixXd::Identity(3, 3);
    // Eigen::MatrixXd m2 = Eigen::MatrixXd::Random(3, 3);
    // Do not use Random() here to not promote use of a non-R RNG
    Eigen::MatrixXd m2 = Eigen::MatrixXd::Zero(3, 3);
    for (auto i=0; i<m2.rows(); i++)
        for (auto j=0; j<m2.cols(); j++)
            m2(i,j) = R::rnorm(0, 1);

    return m1 + 3 * (m1 + m2);
}

If you set the same seed as I do you should get the same matrix

> set.seed(42)
> demoPackage::rcppeigen_hello_world()
        [,1]      [,2]      [,3]
[1,] 8.11288 -1.694095  1.089385
[2,] 1.89859  5.212805 -0.318374
[3,] 4.53457 -0.283977 10.055271
>

Conversion of Rcpp::NumericMatrix to Eigen::MatrixXd

1 Answers1