reading from text file into vector of vectors

[salah_saleh]

Hi!,
I have a text file that contains a 2 dimensional matrix, and I will have to deal with many different files with different matrix dimensions, so I decided to use vector of vectors as they double their size automatically. the problem is that I don't know how to get every line from the file in a separate row of the vector and loop on the cols, and then increment to the next row

int rows = 2; // just an initial size and I rely on doubling the size automatically  
	int cols = 2;
	
	vector<vector<float> > initMatrix(rows,vector<float> (cols));
	
	ifstream myfile("a.text");
	if(!myfile.is_open()) 
	{
		//if file is not opened
		cout<<"Error opening the file"<<endl;
		system("pause");

	}

	while (myfile)
	{
		// I don't know how to get every line from file and loop on the cols. while the cols. size and rows size will change frequently  
	}
	myfile.close();

thanks.

[Clinton Portis]

try this:

int row = 0;
float data = 0.00;
vector<vector<float> > initMatrix(5, vector<float>(cols));

while(myfile)
{
     // --Handle 1D element allocation--
     //Resize every 5 loop iterations (why not? it's more efficient than re-sizing every time)
     //This is make sure you have a 1D element allocated in which to 'push_back()' to

     // **Make sure the initMatrix vector is initialized to at least 5 1D elements**
     if(!(row%5))
     {
          initMatrix.resize(row+5);
     }

     //since you have a set number of columns, we can make a known number of reads per line
     //this will assume three pieces of data per line (3 columns)
     for(int i=0; i<3; i++)
     {
          infile >> data;
          initMatrix[row].push_back(data);
     }

     row++;
}

[salah_saleh]

try this:

int row = 0;
float data = 0.00;

while(myfile)
{
     //since you have a set number of columns, we can make a known number of reads per line
     //this will assume three pieces of data per line (3 columns)
     for(int i=0; i<3; i++)
     {
          infile >> data;
          initMatrix[row].push_back(data);
     }

     row++;
}

thanks for ur reply, but unfortunately both no. of columns and rows are unknown.

[Narue]

You'll want to read a full line, then break it down into columns with something like stringstream:

#include <fstream>
#include <iostream>
#include <sstream>
#include <string>
#include <vector>

int main()
{
    std::ifstream in("test.txt");
    std::vector<std::vector<int> > v;
    
    if (in) {
        std::string line;
        
        while (std::getline(in, line)) {
            v.push_back(std::vector<int>());
            
            // Break down the row into column values
            std::stringstream split(line);
            int value;
            
            while (split >> value)
                v.back().push_back(value);
        }
    }
    
    for (int i = 0; i < v.size(); i++) {
        for (int j = 0; j < v[i].size(); j++)
            std::cout << v[i][j] << ' ';
            
        std::cout << '\n';
    }
}

[salah_saleh]

You'll want to read a full line, then break it down into columns with something like stringstream:

#include <fstream>
#include <iostream>
#include <sstream>
#include <string>
#include <vector>

int main()
{
    std::ifstream in("test.txt");
    std::vector<std::vector<int> > v;
    
    if (in) {
        std::string line;
        
        while (std::getline(in, line)) {
            v.push_back(std::vector<int>());
            
            // Break down the row into column values
            std::stringstream split(line);
            int value;
            
            while (split >> value)
                v.back().push_back(value);
        }
    }
    
    for (int i = 0; i < v.size(); i++) {
        for (int j = 0; j < v[i].size(); j++)
            std::cout << v[i][j] << ' ';
            
        std::cout << '\n';
    }
}

Thank u very much, it worked.