[英]How to sort a vector<pair<string , pair<int , int>>>?
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? 我希望能够根据对<int,int>对的第一个元素对以下向量进行排序 - vector <pair <string,pair <int,int> >>,如果它们相等,则根据它们的第二个对它们进行排序元素,我如何使用STL的构造在C ++中做到这一点?
This sort has to accomplish something on the lines of this 这种方法必须完成这一点
lets say E1 and E2 are 2 elements 假设E1和E2是2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.first == E2.second.first,则必须对第二个元素进行比较。
If you can't use C++11 features you can still do something like this: 如果你不能使用C ++ 11功能,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());
}
[...] based on the 1st element of the pair< int , int> and if those are equal then sort them according to their second elements [...] [...]基于对<int,int>对的第一个元素,如果它们相等,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: std::pair
已经有词典比较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 .second
s of outer pair. 所以,作为WhozCraig指出,应该只是比较.second
小号外部对的。
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C ++ 11,有没有其他方法可行?
Use functor: 使用仿函数:
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(取决于您的需求):
struct LessSecondGeneric
{
template<typename Pair>
bool operator()(const Pair &x, const Pair &y) const
{
return x.second < y.second;
}
};
#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)
sort(x.begin, x.end, [](const X & a, const X & b){return a.second.first < b.second.first ; }) ;
其中x是您的容器,X是元素的类型。
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