C++: sum of columns of a dynamic 2D vector - c++

Question

In C++, how to use a two-dimensional dynamic vector to sum up each column for the matrix in the txt file, and print out the content of the txt file and the result of summing up each column?
After searching through the Internet, I got the following code, but it only sums up a single column. The result I want to get is that no matter how many columns there are in the txt file, I can do the sum of each column.
data.txt figure
#include <iostream>
#include <iomanip>
#include <fstream>
#include <sstream>
#include <vector>
using namespace std;
int main() {
ifstream myfile("data.txt");
if (!myfile.is_open()) {
cout << "Unable to open myfile";
system("pause");
exit(0);
}
vector<string> vec;
string temp;
while (getline(myfile, temp))
{
vec.push_back(temp);
}
vector <float> radius;
cout << "Processing time: " << endl;
for (auto it = vec.begin(); it != vec.end(); it++)
{
cout << *it << endl;
istringstream is(*it);
string s;
int pam = 0;
while (is >> s)
{
if (pam == 0)
{
float r = atof(s.c_str());
radius.push_back(r);
}
pam++;
}
}
cout << "matrix: " << endl;
double sum;
sum = 0;
for (auto it = radius.begin(); it != radius.end(); it++)
{
sum += *it;
}
cout << sum << endl;
system("pause");
return 0;
}
I want to sum each column in the txt file, as shown in the image below:
result

Answer 1

The first thing you should do is not concern yourself with where the data is coming from. Instead, you should write a function that takes the data, regardless of where it comes from, and outputs the totals.
The simplest way to represent the input data is to use a std::vector<std::vector<float>>. Thus a function to create the totals would return a std::vector<float> that represents the totals.
Here is an example of such a function:
#include <vector>
#include <numeric>
// Pass in the data
std::vector<float> getTotals(const std::vector<std::vector<float>>& myData)
{
std::vector<float> totals(myData[0].size());
for (size_t i = 0; i < totals.size(); ++i)
{
// call std::accumulate for each column i
totals[i] = std::accumulate(myData.begin(), myData.end(), 0,
[&](int total, auto& v)
{ return total + v[i]; });
}
// return the totals
return totals;
}
The above function uses std::accumulate to total the values in column i, and store the total for that column in totals[i].
Once this function is written, it can then be tested. Here is a full example:
#include <vector>
#include <numeric>
#include <iostream>
std::vector<float> getTotals(const std::vector<std::vector<float>>& myData)
{
std::vector<float> totals(myData[0].size());
for (size_t i = 0; i < totals.size(); ++i)
{
totals[i] = std::accumulate(myData.begin(), myData.end(), 0,
[&](int total, auto& v)
{ return total + v[i]; });
}
return totals;
}
void printTotals(const std::vector<std::vector<float>>& data,
const std::vector<float>& totals)
{
for (auto& v : data)
{
for (auto& v2 : v)
std::cout << v2 << " ";
std::cout << "\n";
}
std::cout << "Total: ";
for (auto& t : totals)
std::cout << t << " ";
}
int main()
{
std::vector<std::vector<float>> test1 = {{1,2,3},{4,5,6},{7,8,9}};
std::vector<std::vector<float>> test2 = {{1,2,3,4},{4,5,6,8},{7,8,9,10}};
std::vector<std::vector<float>> test3 = {{1,2},{-3,4},{7,8},{34,12},{12,17}};
printTotals(test1, getTotals(test1));
std::cout << "\n\n";
printTotals(test2, getTotals(test2));
std::cout << "\n\n";
printTotals(test3, getTotals(test3));
}
Output:
1 2 3
4 5 6
7 8 9
Total: 12 15 18
1 2 3 4
4 5 6 8
7 8 9 10
Total: 12 15 18 22
1 2
-3 4
7 8
34 12
12 17
Total: 51 43
Once you have this, the next step is to create the std::vector<std::vector<float>> from the data in the file. Once that is created, it is just a simple matter of calling the getTotals() function with that data.
The file reading can be as follows:
#include <istream>
#include <sstream>
#include <vector>
#include <string>
//...
std::vector<std::vector<float>> readData(std::istream& is)
{
std::vector<std::vector<float>> data;
std::string oneLine;
float oneData;
while (std::getline(is, oneLine))
{
std::vector<float> vOneData;
std::istringstream strm(oneLine);
while (strm >> oneData)
vOneData.push_back(oneData);
data.push_back(vOneData);
}
return data;
}
The function is called by simply passing in the stream object (in your case, myfile). The returned value will be a std::vector<std::vector<float>> of the values that were read in.
Putting this all together:
#include <vector>
#include <numeric>
#include <iostream>
#include <istream>
#include <string>
#include <sstream>
std::vector<float> getTotals(const std::vector<std::vector<float>>& myData)
{
std::vector<float> totals(myData[0].size());
for (size_t i = 0; i < totals.size(); ++i)
{
totals[i] = std::accumulate(myData.begin(), myData.end(), 0,
[&](int total, auto& v)
{ return total + v[i]; });
}
return totals;
}
void printTotals(const std::vector<std::vector<float>>& data,
const std::vector<float>& totals)
{
for (auto& v : data)
{
for (auto& v2 : v)
std::cout << v2 << " ";
std::cout << "\n";
}
std::cout << "Total: ";
for (auto& t : totals)
std::cout << t << " ";
}
std::vector<std::vector<float>> readData(std::istream& is)
{
std::vector<std::vector<float>> data;
std::string oneLine;
float oneData;
while (std::getline(is, oneLine))
{
std::vector<float> vOneData;
std::istringstream strm(oneLine);
while (strm >> oneData)
vOneData.push_back(oneData);
data.push_back(vOneData);
}
return data;
}
int main()
{
std::string fileData = "2 3 4 1 5 2\n6 1 2 6 1 8\n8 7 3 9 6 4";
std::istringstream fileDataStream(fileData);
auto dataFromFile = readData(fileDataStream);
printTotals(dataFromFile, getTotals(dataFromFile));
}
Output:
2 3 4 1 5 2
6 1 2 6 1 8
8 7 3 9 6 4
Total: 16 11 9 16 12 14
Note that I didn't use a file stream, but a stringstream to illustrate it doesn't matter how the data is created.