Question

我想用C ++将csv文件解析成2D Map。 csv文件如下所示：

xxx,1,2
xxx,3,4
xxx,5,6
yyy,7,8
yyy,9,10
zzz,11,12
zzz,13,14
zzz,15,16

来自C＃背景，我可以在C＃

中使用几行代码轻松完成

        Dictionary<string, Dictionary<double, int>> mainMap = new Dictionary<string, Dictionary<double, int>>();

        string[] lines = File.ReadAllLines(@"C:\Users\xxx\Desktop\myFile.csv");

        foreach(string line in lines)
        {
            string[] v = line.Split(',');

            if (!mainMap.ContainsKey(v[0]))
                mainMap[v[0]] = new Dictionary<double, int>();

            mainMap[v[0]][Convert.ToDouble(v[1])] = Convert.ToInt32(v[2]);
        }

如何仅使用标准（std）库在C ++中完成相同的操作？

Answer 1

可以继续（假设标准输入）：

#include <iostream>
#include <sstream>
#include <string>
#include <map>

int main(){

    std::string line, token;
    std::stringstream iss;
    std::map<std::string, std::map<double, int>> mainMap;

    std::string key1;
    double key2;
    int val;

    while(std::getline(std::cin, line)){
        iss.clear();
        iss.str(line);

        size_t token_id(0);

        while(std::getline(iss, token, ',')){
            if(token_id == 0){
                key1 = token;

            }else if(token_id == 1){
                key2 = std::stod(token);

            }else if(token_id == 2){
                val = std::stoi(token);
            }
            token_id++;
        }
        mainMap[key1][key2] = val;
    }

    return 0;
}

当然，应该为输入的有效性添加一些检查......

Answer 2

#include <string>
#include <vector>
#include <iostream>
#include <sstream>
#include <fstream>
#include <utility>
#include <map>

typedef std::map<double, int> DoubleIntMap;
typedef std::map<std::string, DoubleIntMap> MyMap;

int main()
{
    MyMap mainMap;

    std::ifstream in("C:/Users/xxx/Desktop/myFile.csv"); // Use forward slashes on Windows too
    if(in.good()) {
        std::string line;
        while(std::getline(in, line)) {
            std::string item;
            std::vector<std::string> parts;
            std::stringstream ss(line);
            while(std::getline(ss, item, ',')) {
                parts.push_back(item);
            }
            if(parts.size() == 3){
                std::string key = parts[0];
                double d = std::stod(parts[1]);
                int i = std::stoi(parts[2]);
                mainMap[key][d] = i;
            }
        }
        // Extra: print them out
        // You can use auto in C++11 instead of MyMap::const_iterator but I prefer the proper type :)
        for(MyMap::const_iterator iter = mainMap.begin(); iter != mainMap.end(); ++iter) {
            const DoubleIntMap& item = iter->second;
            for(DoubleIntMap::const_iterator inner_iter = item.begin(); inner_iter != item.end(); ++inner_iter) {
                std::cout << iter->first << " (" << inner_iter->first << ", " << inner_iter->second << ")\n";
            }
        }
    }
    return 0;
}

将数据解析为C ++ 2D Map

2 个答案: