如何在c ++中的2d数组中插入可变数量的数据

I have the following file input.txt which contains the values :

我有以下文件input.txt,其中包含值:

I want to insert these values to two arrays. I want them to look like this in the end.

我想将这些值插入两个数组。我希望他们最终看起来像这样。

0   0 1 2 3
1   1 4
2   1 4 3

First array will contain the id and second array will contain the elements. I have managed to dynamically allocate memory for these two arrays using the following :

第一个数组将包含id,第二个数组将包含元素。我已设法使用以下方法为这两个数组动态分配内存:

int n,m,i=0,tempNum,lines;
int NumberOfIds=0;
ifstream read("input2.txt");
while(read>>n>>m){
    if (i==0){
        tempNum=n;
    }
    if (tempNum != n){
        NumberOfIds++;
    }
    tempNum = n;
    i++;
}
lines=i-1;

//printf("%d", j);
int** idElements = new int*[NumberOfIds];
int* ids = new int[NumberOfIds];
int* numberOfIdElements = new int[NumberOfIds];

// Rewinds file
read.clear();
read.seekg(0, ios::beg);

int counter = 0;
NumberOfIds=0;
while(read>>n>>m){

    if (tempNum != n){
        numberOfIdElements[NumberOfIds] = counter;
        NumberOfIds++;
        counter = 0;
    }
    tempNum = n;
    counter++;
    i++;
}

for(int k = 0; k < NumberOfIds; ++k)
    idElements[k] = new int[numberOfIdElements[k]];

Now I am stuck in how to insert the data. Any help would be appreciated.

现在我陷入了如何插入数据的困境。任何帮助,将不胜感激。

2 个解决方案

#1

You can do this with std::vector's fairly easily:

你可以很容易地使用std :: vector来做到这一点:

std::vector<std::vector<int>> arr;
while(read>>n>>m){
    //if we're too small, push empty rows till we're big enough
    while(n + 1 > arr.size()) {
        arr.push_back(std::vector<int>());
    }
    arr.at(n).push_back(m); //push m onto row n
}

Alternatively, if your first column numbers become large (so you wouldn't want to make many empty rows), you can use an std::map:

或者,如果您的第一个列号变大(因此您不希望创建许多空行),则可以使用std :: map:

std::map<int, std::vector<int>> arr;
while(read>>n>>m){
    //works because map subscript creates a key/val pair if one doesn't exist
    //so if this row doesn't exist, we get a new vector to push_back to
    arr[n].push_back(m); //push m onto row n
}

See it in action here: ideone

在这里看到它:ideone

#2

Here is another approach using a map of sets:

这是另一种使用集合映射的方法:

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

int main()
{
    std::map<int, std::set<int>> m;
    std::ifstream ifs{"input.txt"};

    // read 
    for(std::string line; std::getline(ifs, line);){
        std::stringstream ss{line};
        int key;
        ss >> key;
        for (int val; ss >> val;)
            m[key].insert(val);
    }

    // print
    for(auto i : m) {
        std::cout << i.first << '\t';
        for(auto j : i.second)
            std::cout << j << ' ';
        std::cout << '\n';
    }
}

You might select other containers depending of your requirements for sorting or preserving duplicates.

您可以根据您的要求选择其他容器进行排序或保留重复项。

#1