Eigen library --> initialize matrix with data from file or existing std::vector content (c++)

Question

My question is how to initialize an eigen Matrix, but NOT this way:

matrix << 1,0,1,0,
          1,0,1,0,
          1,0,1,0,
         


        

Answer 1

I used iterators to collect the data in a vector and then initialize the matrix. The conversion to the vector seem to be the time-consuming part of the method, which approximately has the same speed as the solutions above. Ideas on how to improve this would be interesting.

template 
using Tmat = Eigen::Matrix;

Tmat txt_to_mat(std::string path, int rows, int cols)
{
    std::ifstream fstr(path.c_str());
    std::vector data_vec = std::vector{
        std::istream_iterator(fstr),
        std::istream_iterator()
    };

    Tmat mat(rows, cols);
    for(int i=0; i