how to sort vector with multi data?

问题:

i have such a vector:

struct StatFaces
{
    std::string faceName_1;
    std::string faceName_2;
    float percentagePerson ;
};

std::vector<StatFaces> listFaces_;

and i want to sort that vector. However i want to sort it with group. For example..

I have faceName_1 = john , faceName_2 = kate , percentagePerson = %90
       faceName_1 = john , faceName_2 = nastia , percentagePerson = %95
       faceName_1 = bill , faceName_2 = jamie , percentagePerson = %91 
       faceName_1 = bill , faceName_2 = anna , percentagePerson = %72

output should be ; 

faceName_1 = bill , faceName_2 = jamie, percentagePerson = %91
faceName_1 = bill , faceName_2 = anna , percentagePerson = %72
faceName_1 = john , faceName_2 = nastia , percentagePerson = %95
faceName_1 = john , faceName_2 = kate , percentagePerson = %90

Sort algorithm must group firstName_1 and then sort according to percentagePerson

Ps: I am not good at c++

回答1:

You can pass a custom comparison function to std::sort. This is trivially implementable using std::tie:

#include <tuple> // for std::tie

bool cmp(const StatFaces& lhs, const StatFaces& rhs)
{
  return std::tie(lhs.face_name1, lhs.percentagePerson, lhs.faceName_2) <
         std::tie(rhs.face_name1, rhs.percentagePerson, rhs.faceName_2);
}

then

#include <algorithm> // for std::sort

std::sort(listFaces_.begin(), listFaces_.end(), cmp);

std::tie returns a tuple of lvalue reference to the arguments, and there is a lexicographical less-than comparison bool operator< that compares two of these tuples. The effect is that you perform a less-than lexicographical comparison between two StatFaces instances. This is used internally by std::sort to sort the elements.

Note: std::tie is available in C++11 implementations. If you don't have a C++11 standard library implementation, you can use std::tr1::tie from header <tr1/tuple> or boost::tie. You can also implement the comparison function cmp by hand. That is a good exercise, but it is both tedious and error prone.