Opening and reading a matrix file

Question

0.00/5 (No votes)

See more:

Hey! I am trying to get my file to be read and printed on the screen, i am stuck at it

What I have tried:

#include <iostream>
#include <iomanip>
#include <fstream>
#include <iostream>     // std::cout
#include <functional>   // std::minus
#include <numeric>

int main() {
    std::cout << "Please enter input file name: ";

    std::string iname;

    std::cin >> iname;

    std::ifstream ist {iname};          // ist is an input stream for the file named name
    std::ifstream f("");
    {
        if (f.is_open())
            std::cout << f.rdbuf();
        
    }
    std::cin.get();

}

Posted 16-Oct-19 10:14am

Member 14621201

Updated 17-Oct-19 3:04am

Add a Solution

Comments

Member 14621201 16-Oct-19 16:18pm

the columns are like this:
A Z TKE Y Yerror
118 46 140.0 0.3326E-03 0.6799E-04
118 45 140.0 0.9057E-04 0.1851E-04
118 47 140.0 0.9122E-04 0.1864E-04
119 46 140.0 0.7077E-04 0.2217E-04
119 45 140.0 0.5748E-05 0.1800E-05
119 47 140.0 0.6486E-04 0.2032E-04
120 47 140.0 0.3259E-03 0.7113E-04
120 46 140.0 0.1016E-03 0.2217E-04
120 48 140.0 0.7759E-04 0.1694E-04

and i need to add 3rd column the Y for each A (A runs from 118 to 165), for all 118 in the lines to keep adding the Y

Patrice T 16-Oct-19 16:35pm

Use Improve question to update your question.
So that everyone can pay attention to this information.

Member 14621201 16-Oct-19 17:48pm

ok i will do it asap

2 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Visweswaran N · Accepted Answer · 2019-10-16T15:07:00

I wrote a small helper function which will help, have added comments to help you understand.

C++

// SWAMI KARUPPASWAMI THUNNAI

#include <iostream>
// As content of the file is in strings.
#include <string>
// For file IO
#include <fstream>
// For Matix storing
#include <vector>


std::vector<std::vector<double>> get_matrix(std::string file_path, char sep)
{
	std::vector<std::vector<double>> mat;
	std::ifstream file;
	file.open(file_path);
	// Throw exception if you want to
	if(!file.is_open())
	{
		return mat;
	}
	while(!file.eof())
	{
		std::string row;
		std::getline(file, row);
		std::vector<double> row_vec;
		std::string row_value = "";
		for(char c : row)
		{
			// If the character is seperator
			if(c == sep)
			{
				// Convert the string to double and append it and reset the string
				row_vec.push_back(std::stod(row_value));
				row_value = "";
			}
			else
			{
				row_value += c;
			}
		}
		// If the string is not empty append the last value [Last value generally gets ignored as there is no seperator afterwards]
		if(row_value.size() != 0)
		{
			row_vec.push_back(std::stod(row_value));
			row_value = "";
		}
		// Append the row now
		mat.push_back(row_vec);
	}
	file.close(); // Always close the opened file
	return mat;
}


int main()
{
	std::vector<std::vector<double>> mat = get_matrix("mat.txt", ' ');
	// Let's display our matrix
	for(auto i: mat)
	{
		for(auto j: i) std::cout << j << " ";
		std::cout << "\n";
	}
}

My file contents:

118 46 140.0
118 45 140.0
118 47 140.0

Output:

g++ -std=c++11 main.cpp -o test.exe

118 46 140
118 45 140
118 47 140

Note: Robustness is inversely proportional to accuracy [Code Complete 2]. This code might be accurate but it is not robust. Even a small white space might break this code.

Trimming the strings, and dealing with other things like shape is your own quest.

CPallini · Accepted Answer · 2019-10-17T03:05:00

Try also

C++

#include <iostream>
#include <vector>
#include <utility>
#include <map>
#include <numeric>

using namespace std;
int main()
{ 
  vector < pair < int, double> > vp;
  multimap<int, double> mm;
  string line; 
  getline(cin, line); // skip header line
  
  for (;;)
  { 
    int id,z;
    double tke, y, yerror;
    cin >> id >> z >> tke >> y >> yerror;
    if ( ! cin ) break;
    mm.emplace( id, y);
  }
  auto it_begin = mm.begin(); 
  while (it_begin != mm.end() )
  { 
    auto it_end = mm.upper_bound(it_begin->first);
    auto sumfun = [] (double a, pair < int, double> p) {return a + p.second;};

    double sum = accumulate(it_begin, it_end, 0.0, sumfun);
    vp.push_back( make_pair(it_begin->first, sum));
    it_begin = it_end;
  }
  
  cout << "id ysum" << endl;
  for (auto p : vp) 
    cout << p.first << " " << p.second << endl;
}

Run it redirecting your data file as standard input.

Used with the following input data

A Z TKE Y Yerror
118 46 140.0 0.3326E-03 0.6799E-04
118 45 140.0 0.9057E-04 0.1851E-04
118 47 140.0 0.9122E-04 0.1864E-04
119 46 140.0 0.7077E-04 0.2217E-04
119 45 140.0 0.5748E-05 0.1800E-05
119 47 140.0 0.6486E-04 0.2032E-04
120 47 140.0 0.3259E-03 0.7113E-04
120 46 140.0 0.1016E-03 0.2217E-04
120 48 140.0 0.7759E-04 0.1694E-04

It produces the output

id ysum
118 0.00051439
119 0.000141378
120 0.00050509

Opening and reading a matrix file

2 solutions

Solution 1

Solution 2

Add your solution here

Preview 0