c ++向量库_在C ++中对2D向量进行排序

冷不防 2023-03-05 09:46 20阅读 0赞

c ++向量库

As per as a [2D vector][] is concerned it's a [vector of a 1D vector][]. But what we do in sorting a 1D vector like,

就[2D向量][2D vector]而言，它[是1D向量的向量][vector of a 1D vector] 。 但是我们在对一维向量进行排序时所做的工作

sort(vector.begin(),vector.end());

We can't do the same for a 2D vector without any user-defined comparator function, as it will merely sort based on the first element of each column.

没有任何用户定义的比较器函数，我们无法对2D向量执行相同的操作，因为它只会根据每列的第一个元素进行排序。

But we can sort 2D vector based on use cases:

但是我们可以根据用例对2D向量进行排序：

## 1)根据特定的行排序 **(**1) Sort based on a particular row**)** ##

The below example sorts a particular row in the 2D vector.

下面的示例对2D向量中的特定行进行排序。

Say for example, the 2D matrix is:

例如，二维矩阵为：

[[3, 5, 4],
    [6, 4, 2],
    [1, 7, 3]]

So if we sort the first row in ascending order the output will be:

因此，如果我们以升序对第一行进行排序，则输出将是：

[[3, 4, 5],
    [6, 4, 2],
    [1, 7, 3]]

#include <bits/stdc++.h>
    using namespace std;
    
    void print(vector<vector<int> > two_D_vector)
    {
        for (auto it : two_D_vector) {
            //it is now an 1D vector
            for (auto ij : it) {
                cout << ij << " ";
            }
            cout << endl;
        }
    }
    
    int main()
    {
        //2D vector initialized with 
        //user-defined elements only
        vector<vector<int> > two_D_vector{
            { 3, 5, 4 },
            { 6, 4, 2 },
            { 1, 7, 3 }
        };
    
        //printing the 2D vector
        cout << "printing the 2D vector before sorting\n";
        print(two_D_vector);
    
        //sorting the 2D array based on a particular row
        //here we sort the first row of the 2D vector
        //so, basically we sort the 1D array(the first row)
        sort(two_D_vector[0].begin(), two_D_vector[0].end());
    
        //print the 2D vector
        cout << "printing the 2D vector after sorting\n";
    
        print(two_D_vector);
    
        return 0;
    }

**Output:**

**输出：**

printing the 2D vector before sorting
    3 5 4
    6 4 2
    1 7 3
    printing the 2D vector after sorting
    3 4 5
    6 4 2
    1 7 3

So if we sort the first row in descending order the output will be:

因此，如果我们以降序对第一行进行排序，则输出将是：

[[3, 5, 4],
    [6, 4, 2],
    [7, 3, 1]]

#include <bits/stdc++.h>
    using namespace std;
    
    void print(vector<vector<int> > two_D_vector)
    {
        for (auto it : two_D_vector) {
            //it is now an 1D vector
            for (auto ij : it) {
                cout << ij << " ";
            }
            cout << endl;
        }
    }
    
    int main()
    {
        //2D vector initialized with 
        //user-defined elements only
        vector<vector<int> > two_D_vector{
            { 3, 5, 4 },
            { 6, 4, 2 },
            { 1, 7, 3 }
        };
    
        //printing the 2D vector
        cout << "printing the 2D vector before sorting\n";
        print(two_D_vector);
    
        //sorting the 2D array based on a particular row
        //here we sort the last row of the 2D vector 
        //in descending order
        //so, basically we sort the 1D array in 
        //descending order(the last row)
        sort(two_D_vector[2].begin(), two_D_vector[2].end(), greater<int>());
    
        //print the 2D vector
        cout << "printing the 2D vector after sorting\n";
    
        print(two_D_vector);
    
        return 0;
    }

**Output:**

**输出：**

printing the 2D vector before sorting
    3 5 4
    6 4 2
    1 7 3
    printing the 2D vector after sorting
    3 5 4
    6 4 2
    7 3 1

## 2)根据特定的列排序 **(**2) Sort based on a particular column**)** ##

The below example sorts a particular column in the 2D vector.

下面的示例对2D向量中的特定列进行排序。

Say for example, the 2D matrix is:

例如，二维矩阵为：

[[3, 5, 4],
    [6, 4, 2],
    [1, 7, 3]]

So if we sort the first column in ascending order the output will be:

因此，如果我们以升序对第一列进行排序，则输出将是：

[[1, 4, 5],
    [3, 4, 2],
    [6, 7, 3]]

Here we need to define our user-defined comparator function to do the above thing. Like we will take each element of the 2D vector (which is a 1D vector, to be specific each row) and compare based on the first element (or any particular element) only. That's why we need a [user-defined comparator][].

在这里，我们需要定义用户定义的比较器函数来完成上述操作。 就像我们将采用2D向量的每个元素(这是1D向量，每一行都是特定的)并仅基于第一个元素(或任何特定元素)进行比较。 这就是为什么我们需要一个[用户定义的比较器][user-defined comparator] 。

#include <bits/stdc++.h>
    using namespace std;
    
    void print(vector<vector<int> > two_D_vector)
    {
        for (auto it : two_D_vector) {
            //it is now an 1D vector
            for (auto ij : it) {
                cout << ij << " ";
            }
            cout << endl;
        }
    }
    
    bool mycomp(vector<int>& A, vector<int>& B)
    {
        //if first element of first 
        //row<first element of second row
        if (A[0] < B[0])
            return true; //no swap
        //other wise swap the rows
        return false;
    }
    
    int main()
    {
        //2D vector initialized with 
        //user-defined elements only
        vector<vector<int> > two_D_vector{
            { 3, 5, 4 },
            { 6, 4, 2 },
            { 1, 7, 3 }
        };
    
        //printing the 2D vector
        cout << "printing the 2D vector before sorting\n";
        print(two_D_vector);
    
        //sorting the 2D array based on a particular row
        //here we sort the last row of the 2D vector 
        //in descending order
        //so, basically we sort the 1D array in 
        //descending order(the last row)
        sort(two_D_vector.begin(), two_D_vector.end(), mycomp);
    
        //print the 2D vector
        cout << "printing the 2D vector after sorting\n";
    
        print(two_D_vector);
    
        return 0;
    }

**Output:**

**输出：**

printing the 2D vector before sorting
    3 5 4
    6 4 2
    1 7 3
    printing the 2D vector after sorting
    1 7 3
    3 5 4
    6 4 2

To sort in descending order, we need to just change the comparator function.

要按降序排序，我们只需要更改比较器功能即可。

#include <bits/stdc++.h>
    using namespace std;
    
    void print(vector<vector<int> > two_D_vector)
    {
        for (auto it : two_D_vector) {
            //it is now an 1D vector
            for (auto ij : it) {
                cout << ij << " ";
            }
            cout << endl;
        }
    }
    //to sort based on column in descending order
    bool mycomp(vector<int>& A, vector<int>& B)
    {
        //if first element of first 
        //row<first element of second row
        if (A[0] < B[0])
            return false; //swap the rows
        //other wise  no swap
        return true;
    }
    
    int main()
    {
        //2D vector initialized with 
        //user-defined elements only
        vector<vector<int> > two_D_vector{
            { 3, 5, 4 },
            { 6, 4, 2 },
            { 1, 7, 3 }
        };
    
        //printing the 2D vector
        cout << "printing the 2D vector before sorting\n";
        print(two_D_vector);
    
        //sorting the 2D array based on a particular row
        //here we sort the last row of the 2D vector 
        //in descending order
        //so, basically we sort the 1D array in 
        //descending order(the last row)
        sort(two_D_vector.begin(), two_D_vector.end(), mycomp);
    
        //print the 2D vector
        cout << "printing the 2D vector after sorting\n";
        print(two_D_vector);
        
        return 0;
    }

**Output:**

**输出：**

printing the 2D vector before sorting
    3 5 4
    6 4 2
    1 7 3
    printing the 2D vector after sorting
    6 4 2
    3 5 4
    1 7 3

There can be various use cases to sort a 2D vector and we need to write our comparator functions.

可以使用各种用例对2D向量进行排序，我们需要编写比较器函数。

**Exercises**

**练习题**

**(a) Sort based on row sizes in ascending order**

**(a)根据行大小升序排序**

Say the 2D vector is
    {
    {2, 3, 4, 5},
    {3, 4, 1},
    {1}}
    
    After sorting the 2D vector based on 
    row size in ascending order:
    {
    {1},
    {3, 4, 1},
    {2, 3, 4, 5}
    }

Here we need to use our user define a function which will swap the rows as per their sizes.

在这里，我们需要使用用户定义的函数，该函数将根据行的大小交换行。

#include <bits/stdc++.h>
    using namespace std;
    
    void print(vector<vector<int> > two_D_vector)
    {
        for (auto it : two_D_vector) {
            //it is now an 1D vector
            for (auto ij : it) {
                cout << ij << " ";
            }
            cout << endl;
        }
    }
    
    //to sort based on column in descending order
    bool mycomp(vector<int>& A, vector<int>& B)
    {
        //if first row size>second row size
        if (A.size() > B.size())
            return false; //swap the rows
        //other wise  no swap
        return true;
    }
    
    int main()
    {
        //2D vector initialized with 
        //use- defined elements only
        vector<vector<int> > two_D_vector{
            { 2, 3, 4, 5 },
            { 3, 4, 1 },
            { 1 }
        };
    
        //printing the 2D vector
        cout << "printing the 2D vector before sorting\n";
        print(two_D_vector);
    
        //sorting the 2D array based on a particular row
        //here we sort the last row of the 2D vector 
        //in descending order
        //so, basically we sort the 1D array in 
        //descending order(the last row)
        sort(two_D_vector.begin(), two_D_vector.end(), mycomp);
    
        //print the 2D vector
        cout << "printing the 2D vector after sorting\n";
    
        print(two_D_vector);
    
        return 0;
    }

**Output:**

**输出：**

printing the 2D vector before sorting
    2 3 4 5
    3 4 1
    1
    printing the 2D vector after sorting
    1
    3 4 1
    2 3 4 5

**(b) Can you sort based on column size anyway?**

**(b)仍然可以根据列大小进行排序吗？**

If you can't sort in that way, then do comment why you cant?

如果您无法通过这种方式进行排序，那么请评论一下您为什么不能这样做？

> 翻译自: [https://www.includehelp.com/stl/sort-a-2d-vector-in-cpp.aspx][https_www.includehelp.com_stl_sort-a-2d-vector-in-cpp.aspx]

c ++向量库

[2D vector]: https://www.includehelp.com/stl/initialize-2d-vector-in-cpp-in-different-ways.aspx
[vector of a 1D vector]: https://www.includehelp.com/stl/initialize-a-vector-in-cpp-in-different-ways.aspx
[user-defined comparator]: https://www.includehelp.com/stl/user-defined-comparator-for-priority-queue-in-cpp-stl.aspx
[https_www.includehelp.com_stl_sort-a-2d-vector-in-cpp.aspx]: https://www.includehelp.com/stl/sort-a-2d-vector-in-cpp.aspx