// open the file for importing data
        ifstream myfile("test_data.txt");
        if (myfile.is_open())
        {

            // eof allows all the rows of data to be converted one at a time
            while (!myfile.eof())
            {
                getline (myfile, bLine); // grab the immediate line as a string

                // this next while loop converts the row at hand into individual strings, which are converted to type double.
                while (bLine.find(",", 0) != string::npos) // loop until there isn't a comma
                {
                    int comma_pos = bLine.find(",", 0); // look for the comma position
                    double value = atof(bLine.substr(0, comma_pos).c_str());
                    temp.push_back(value);
                    bLine = bLine.substr(comma_pos + 1, bLine.size() - comma_pos - 1);  //  remove the substring before the first comma

                }

            // the final value, which doesn't have a comma after it, hasn't been extracted
            temp.push_back(atof(bLine.c_str()));
            // push back temporary 1D row vector into the 2D vector
            data.push_back(temp);
            // add one to the rowcount
            rowcount++;
            // the above section will loop for each row - pushing each row's numbers to the data vector, and counting the rows
            }

            // close the file after reading from it
            cout << "There are " << rowcount << " rows in the CSV file.\n";
            myfile.close();

        }