How to read file as vector>?

问题:

I have data like this

4.0 0.8
4.1 0.7
4.4 1.1
3.9 1.2
4.0 1.0

I have written my program

#include <string>
#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

int main() {
vector<double> v;
ifstream in("primer.dat");
double word;
while(in >> word)
v.push_back(word);
for(int i = 0; i < v.size(); i++)
cout << v[i] << endl;
}

But now I have realized that for further calculations in my code,I need data as (vector <vector> double).I would prefer not to reshape the vector.Is it possible to read data as vector of vectors?

回答1:

Try the following

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

int main()
{
    std::vector<std::vector<double>> v;
    std::ifstream in( "primer.dat" );
    std::string record;

    while ( std::getline( in, record ) )
    {
        std::istringstream is( record );
        std::vector<double> row( ( std::istream_iterator<double>( is ) ),
                                 std::istream_iterator<double>() );
        v.push_back( row );
    }

    for ( const auto &row : v )
    {
        for ( double x : row ) std::cout << x << ' ';
        std::cout << std::endl;
    }        
}    

回答2:

Not sure if I fully understand what you meant but if I did this code should work just fine then:

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

using namespace std;

std::vector<std::string> split(const std::string& str, char sep)
    {
        std::vector<std::string> result;
        std::istringstream iss(str);
        std::string sub;
        while (std::getline(iss, sub, sep))
            result.push_back(sub);
        return result;
    }

int main() {
    vector<vector<double> >  completeVector ;
    ifstream in("primer.dat");
    string word;
    while(in >> word){
        std::vector<std::string> splitS = split(word, ' ');
        std::vector<double> line ;
        for(int i = 0 ; i < splitS.size() ; i++){
            line.push_back(stod(splitS[i]));
        }
        completeVector.push_back(line);
    }

// For printing out the result
    for(int i = 0 ; i < completeVector.size() ; i++){
        std::vector<double> tmp = completeVector[i];
        for(int j = 0 ; j < tmp.size() ; j++){
            std::cout << tmp[j] << std::endl ;
        }
     }  
}

It compiles for sure and it should have the behaviour that you're looking for. If it doesn't let me know in the comments.

回答3:

#include <string>
#include <sstream>
#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

int main() {
  vector<vector<double>> v;
  ifstream in("primer.dat");
  string line;
  while(std::getline(in, line))
  {
    v.push_back(vector<double>());
    stringstream ss(line);
    double word;
    while(ss >> word)
    {
      v.back().push_back(word);
    }
  }
  for(int i = 0; i < v.size(); i++)
  {
    for(int j = 0; j < v[i].size(); j++)
    {
      cout << v[i][j] << ' ';
    }
    cout << endl;
  }

}