如何排序一个向量>>?

I want to be able to sort the following vector - vector< pair< string , pair< int ,int > > > based on the 1st element of the pair< int , int> and if those are equal then sort them according to their second elements, how do I do that in C++ using STL's constructs?

后我希望能够排序向量,向量 <对<字符串,对< int,int> > >基于第一元素的< int,int >,如果这些是相等的然后他们根据他们的第二个元素排序,我该怎么做在c++中使用STL的构造吗?

This sort has to accomplish something on the lines of this

这种类型必须在这方面有所作为

lets say E1 and E2 are 2 elements

假设E1和E2是两个元素。

if E1.second.first == E2.second.first then the comparison must be made with respect to the second elements.

如果E1.second。第一次= = E2.second。首先，必须对第二要素进行比较。

3 个解决方案

#1

If you can't use C++11 features you can still do something like this:

如果你不能使用c++ 11的特性，你仍然可以这样做:

typedef std::pair<std::string, std::pair<int, int>> AnkitSablok;

struct my_compare {
    bool operator()(const AnkitSablok &lhs, const AnkitSablok &rhs) const {
        return lhs.second < rhs.second;
    }
};

int main()
{
    std::vector<AnkitSablok> vec;

    std::sort(vec.begin(), vec.end(), my_compare());
}

#2

[...] based on the 1st element of the pair< int , int> and if those are equal then sort them according to their second elements [...]

[…]基于这一对的第一个元素< int, int>，如果它们是相等的，那么根据它们的第二个元素对它们进行排序[…]

std::pair already has lexicographical comparison C++03 20.2.2/6:

:对已经有字典比较的C+ 03 20.2.2/6:

template <class T1, class T2>
bool operator<(const pair<T1, T2>& x, const pair<T1, T2>& y);

Returns: x.first < y.first || (!(y.first < x.first) && x.second < y.second)

So, as WhozCraig pointed out, you should just compare .seconds of outer pair.

所以，正如WhozCraig所指出的，你应该比较外部对的。秒。

This is a lambda expression, I dont have C++ 11 with me, is there no other way possible?

这是一个lambda表达式，我没有带c++ 11，难道没有其他方法吗?

Use functor:

使用函子:

struct LessSecond
{
    template<typename T, typename U>
    bool operator()(const std::pair<T,U> &x, const std::pair<T,U> &y) const
    {
        return x.second < y.second;
    }
};
// ...
sort(x.begin(), x.end(), LessSecond());

Or maybe more generic version (depends on your needs):

或者更通用的版本(取决于你的需要):

struct LessSecondGeneric
{
    template<typename Pair>
    bool operator()(const Pair &x, const Pair &y) const
    {
        return x.second < y.second;
    }
};

LIVE DEMO:

现场演示:

#include <algorithm>
#include <iostream>
#include <iterator>
#include <utility>
#include <vector>

struct LessSecond
{
    template<typename T, typename U>
    bool operator()(const std::pair<T,U> &x, const std::pair<T,U> &y) const
    {
        return x.second < y.second;
    }
};

int main()
{
    using namespace std;

    vector<pair<string , pair<int, int>>> x
    {
        {"1", {2, 1}}, {"2", {1, 1}}, {"3", {1, 2}}
    };
    sort(x.begin(), x.end(), LessSecond());
    for(const auto &p : x)
        cout << p.first << " (" << p.second.first << ", " << p.second.second << ")" << endl;
}

Output is:

输出是:

2 (1, 1)
3 (1, 2)
1 (2, 1)

#3

sort(x.begin, x.end, [](const X & a, const X & b){return a.second.first < b.second.first ; }) ;

Where x is your container, and X is the type of an element.

其中x是容器，x是元素的类型。

#1