Question

我有一个数据列表（在4列中），我想按某列排序。它从文件读入2D矢量。我使用了std :: sort方法并编写了我的比较器函子。程序编译并运行，但是当我打印前10个元素时，它没有排序，但肯定不同于它添加到2D矢量的顺序。

以下是代码：

#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);
}

编辑 - 输入文件的样本：
编辑2 - 在4

中交换了line_count和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

依此类推另外87k行左右。

Answer 1

我有一个数据列表（在4列中），我想用a排序某栏。

问题是用于在OP程序中存储数据的向量向量的维数在声明和使用之间是不一致的。

一个小问题是while(!infile.eof()){...使用了should be avoided。

固定版本是这样的：

#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;
}

给出示例数据的输出是：

   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

排序双向的2D矢量

1 个答案: