Question

我有一个项目，告诉我导入一个csv文件，然后对其进行排序（该文件包含数百万个数字）。我用谷歌搜索了一个合并排序的源代码，发现了这个，我尝试了一下，排序工作了。（我通过Virtual Box用g ++在ubuntu中编译了此代码）。

#include<iostream>
#include<vector>

using namespace std;

void print(vector<int> v)
{
  for(int i = 0; i < v.size(); i++) cout << v[i] << " ";
  cout << endl;
}

vector<int> merge(vector<int> left, vector<int> right)
{
   vector<int> result;
   while ((int)left.size() > 0 || (int)right.size() > 0) {
      if ((int)left.size() > 0 && (int)right.size() > 0) {
         if ((int)left.front() <= (int)right.front()) {
            result.push_back((int)left.front());
            left.erase(left.begin());
         } 
   else {
            result.push_back((int)right.front());
            right.erase(right.begin());
         }
      }  else if ((int)left.size() > 0) {
            for (int i = 0; i < (int)left.size(); i++)
               result.push_back(left[i]);
            break;
      }  else if ((int)right.size() > 0) {
            for (int i = 0; i < (int)right.size(); i++)
               result.push_back(right[i]);
            break;
      }
   }
   return result;
}

vector<int> mergeSort(vector<int> m)
{
   if (m.size() <= 1)
      return m;

   vector<int> left, right, result;
   int middle = ((int)m.size()+ 1) / 2;

   for (int i = 0; i < middle; i++) {
      left.push_back(m[i]);
   }

   for (int i = middle; i < (int)m.size(); i++) {
      right.push_back(m[i]);
   }

   left = mergeSort(left);
   right = mergeSort(right);
   result = merge(left, right);

   return result;
}

int main()
{
   vector<int> v;

   v.push_back(38);
   v.push_back(27);
   v.push_back(43);
   v.push_back(3);
   v.push_back(9);
   v.push_back(82);
   v.push_back(10);

   print(v);
   cout << "------------------" << endl;

   v = mergeSort(v);

   print(v);
}

但是当我插入代码以导入csv文件时，它仅读取该文件并且排序未运行，我将其放置错了吗？这是我的代码：

#include <fstream>
#include <iostream>
#include <vector>
#include <string>
#include <stdio.h>
#include <cstdlib>
#include <stdlib.h>

using namespace std;

const int jumlahData = 999999;
double data[jumlahData] = {0};

void loadData(const char* namaFile) {
    string line;
    ifstream myfile (namaFile);

    if (myfile.is_open()) {
        int counter = 0;
        while (getline(myfile, line, ',')) {
            //cout << line << '\n';
            data[counter] = stod(line);
            counter++;
        }
        myfile.close();
    }
}

void print(vector<int> v)
{
  for(int i = 0; i < v.size(); i++) cout << v[i] << " ";
  cout << endl;
}

vector<int> merge(vector<int> left, vector<int> right)
{
   vector<int> result;
   while ((int)left.size() > 0 || (int)right.size() > 0) {
      if ((int)left.size() > 0 && (int)right.size() > 0) {
         if ((int)left.front() <= (int)right.front()) {
            result.push_back((int)left.front());
            left.erase(left.begin());
         } 
   else {
            result.push_back((int)right.front());
            right.erase(right.begin());
         }
      }  else if ((int)left.size() > 0) {
            for (int i = 0; i < (int)left.size(); i++)
               result.push_back(left[i]);
            break;
      }  else if ((int)right.size() > 0) {
            for (int i = 0; i < (int)right.size(); i++)
               result.push_back(right[i]);
            break;
      }
   }
   return result;
}

vector<int> mergeSort(vector<int> m)
{
   if (m.size() <= 1)
      return m;

   vector<int> left, right, result;
   int middle = ((int)m.size()+ 1) / 2;

   for (int i = 0; i < middle; i++) {
      left.push_back(m[i]);
   }

   for (int i = middle; i < (int)m.size(); i++) {
      right.push_back(m[i]);
   }

   left = mergeSort(left);
   right = mergeSort(right);
   result = merge(left, right);

   return result;
}

int main()
{
   vector<int> v;

   loadData("dataDemo.csv");

   print(v);
   cout << "------------------" << endl;

   v = mergeSort(v);

   print(v);
}

Answer 1

您的loadData("dataDemo.csv");调用不会写入先前声明的本地vector<int> v;。您的向量v没有元素。您需要编写一种基于v的内容填充向量double data[jumlahData]的方法即..

int main()
{
   vector<int> v;

   loadData("dataDemo.csv");
   populateVectorWithData(v, data); //TODO implement me
   print(v);
   cout << "------------------" << endl;

   v = mergeSort(v);

   print(v);
}

Answer 2

正如其他人指出的那样，您没有对读入的实际数据进行排序。这可以通过返回读入的数据点数来轻松解决。

一种更好的方法（我怀疑您正在尝试）是将向量的引用从main发送到loadData，并push_back将向量上的数据发送出去。此外，建议尽可能使用实现提供的库。换句话说，不要重新发明轮子，而只使用<algorithm>而不是您自己或其他人的排序算法。它有助于防止令人讨厌的错误。

int main()
{
  //return the count of integers read into data[] in loadData()
  //also change the vector & array types to be consistent, please!
  std::vector<int> v (data, loadData("dataDemo.csv");

  print(v);   //print the loaded vector
  cout << "------------------" << endl;

  std::sort(v.begin(), v.end());  // using <algorithm> (̶i̶t̶'̶s̶ ̶q̶u̶i̶c̶k̶s̶o̶r̶t̶)̶

  print(v);
}

导入csv文件，然后使用c ++对其进行排序

2 个答案: