How to read CSV file and assign to Eigen Matrix?

Question

I try to read a large cvs file into Eigen Matrix, below the code found having problem where it can not detect each line of \\n in cvs file to create multiple rows in the mat

Answer 1

Here's something you can actually copy-paste

Writing your own "parser"

Pros: lightweight and customizable

Cons: customizable

#include 
#include 
#include 

using namespace Eigen;

template
M load_csv (const std::string & path) {
    std::ifstream indata;
    indata.open(path);
    std::string line;
    std::vector values;
    uint rows = 0;
    while (std::getline(indata, line)) {
        std::stringstream lineStream(line);
        std::string cell;
        while (std::getline(lineStream, cell, ',')) {
            values.push_back(std::stod(cell));
        }
        ++rows;
    }
    return Map>(values.data(), rows, values.size()/rows);
}

Usage:

MatrixXd A = load_csv("C:/Users/.../A.csv");
Matrix3d B = load_csv("C:/Users/.../B.csv");
VectorXd v = load_csv("C:/Users/.../v.csv");

Using the armadillo library's parser

Pros: supports other formats as well, not just csv

Cons: extra dependency

#include 

template 
M load_csv_arma (const std::string & path) {
    arma::mat X;
    X.load(path, arma::csv_ascii);
    return Eigen::Map(X.memptr(), X.n_rows, X.n_cols);
}