Sorting a 2D vector of doubles - c++

Question

I have a list of data (in 4 columns) that I would like to sort by a certain column. It was read in from a file to a 2D vector. I the used the std::sort method and wrote my comparator functor. The program compiles and runs, but when I print the first 10 elements it is not sorted, but is certainly different from the order it was added to the 2D vector.
Here is the code:
#include <iostream>
#include <fstream>
#include <stdio.h>
#include <string>
#include <vector>
#include <algorithm>
#include <iomanip>
using namespace std;
typedef vector<double> Row;
typedef vector<Row> Matrix;
bool sortByFourthColumn(const Row& row1, const Row& row2){
return (double) row1[3] < (double) row2[3];
}
int main(){
std::ifstream infile;
infile.open("Test8_Output.txt");
double x,y,z,E;
char line[200];
int line_count=0;
ofstream outfile;
outfile.open("WO_crp.txt");
if (infile.is_open()){
while (!infile.eof()){
infile.getline(line,170);
if (line[0] != '%'){
outfile<<line<<"\n";
line_count++;
}
else{
}
}
Matrix data(line_count,Row(4));
outfile.close();
std::ifstream myfile;
myfile.open("WO_crp.txt");
int i = 0;
while(myfile >> x >> y >> z >> E){
data[0][i] = x;
data[1][i] = y;
data[2][i] = z;
data[3][i] = E;
i++;
}
myfile.close();
std::sort(data.begin(), data.end(), sortByFourthColumn);
for (int u = 0; u <20; u++){
cout << setprecision(5) << data[0][u] << "\t" << setprecision(5)<< data[1][u] << "\t" << setprecision(5)<< data[2][u] << "\t" << setprecision(5)<< data[3][u] << endl;
}
}
else{
cout << "Error: File is invalid.\n";
}
return(0);
}
EDIT - Sample of what the input file looks like:
EDIT 2 - swapped 4 and line_count in Matrix data(4,Row(line_count));
% Model: CDS_Test8.mph
% Version: COMSOL 5.2.0.220
% Date: Jul 13 2016, 14:33
% Dimension: 3
% Nodes: 86183
% Expressions: 1
% Description: Electric field norm
% Length unit: m
% x y z es.normE (V/m)
0.13774675805195374 0.05012986567931247 0.20735 67.35120820901535
0.13870000000000005 0.04957489750396299 0.20735000000000003 102.8772500513651
0.13870000000000002 0.050800000000000005 0.20735 87.56008679032011
0.13792733849817027 0.050131465727838186 0.20801419247484804 73.55192534768238
0.13674627634411463 0.04992349737428063 0.20735 63.23018910026428
0.13750191177019236 0.0508 0.20735000000000003 67.26176884022838
0.13827743496772454 0.05193409099097887 0.20734999999999998 73.35474409597487
0.13803618792088135 0.05134931748395268 0.20841988134890965 75.3712126982815
0.13905949760011943 0.05141879754884912 0.20734999999999998 83.70739713476813
0.13896970815034013 0.05092428105421264 0.208142746399683 84.73571510992372
0.1390220807917094 0.0501245422629353 0.20817502757007986 85.57119242707628
0.13944867847480893 0.05161480113017738 0.2081969878426443 89.65643851109644
And so on it goes for another 87k lines or so.

Answer 1

I have a list of data (in 4 columns) that I would like to sort by a
certain column.
The problem is that the dimensions of the vector of vectors used to store the data in OP program is not consistent between declaration and use.
A minor problem is the use of while(!infile.eof()){... which should be avoided.
A fixed version is like this:
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <vector>
#include <array>
#include <algorithm>
#include <iomanip>
using Row = std::array<double,4>; // instead of typedefs
using Matrix = std::vector<Row>;
using std::cout;
bool sortByFourthColumn(const Row& row1, const Row& row2){
return row1[3] < row2[3];
// ^ The cast is unnecessary
}
int main(){
std::string file_name{"Test8_Output.txt"};
std::ifstream infile{file_name, std::ios_base::in};
if ( !infile ) {
cout << "Error: unable to open file " << file_name << '\n';
return EXIT_FAILURE;
}
Matrix data;
data.reserve(90000); // if you are afraid of the reallocations
int count = 0;
std::string line;
// instead of two loops you can use one loop and read the file once
// I'll use std::getline to extract a row in a std::string
while ( std::getline(infile, line) ) {
// skip comments and empty lines
if ( line.empty() || line[0] == '%' )
continue;
++count;
// extract data from the string using a stringstream
std::stringstream ss{line};
Row r;
ss >> r[0] >> r[1] >> r[2] >> r[3];
if ( !ss ) {
cout << "Format error in line " << count << " of file.\n";
break;
}
data.push_back(std::move(r));
}
std::sort(data.begin(), data.end(), sortByFourthColumn);
cout << std::setprecision(5) << std::fixed;
for ( const auto & r : data ) {
for ( auto const &x : r ) {
cout << std::setw(10) << x;
}
cout << '\n';
}
return EXIT_SUCCESS;
}
The output, given the example data is:
0.13675 0.04992 0.20735 63.23019
0.13750 0.05080 0.20735 67.26177
0.13775 0.05013 0.20735 67.35121
0.13828 0.05193 0.20735 73.35474
0.13793 0.05013 0.20801 73.55193
0.13804 0.05135 0.20842 75.37121
0.13906 0.05142 0.20735 83.70740
0.13897 0.05092 0.20814 84.73572
0.13902 0.05012 0.20818 85.57119
0.13870 0.05080 0.20735 87.56009
0.13945 0.05161 0.20820 89.65644
0.13870 0.04957 0.20735 102.87725