Sort vector of class objects based on some member variable

问题

Let

class Record {

    public:
       Record();

    private:
       string id;
       double score;
};

Somewhere we define a vector of Record objects, i.e.,

vector<Record> records(N);
// Initialize records somehow

I would like to sort records based on score (in descending order) keeping track of the other member variables of Record (in this case just the score, but in general whatever else).

回答1:

You can implement the comparison operators.

bool Record::operator<(const Record& rhs) {
  return score < rhs.score;
}

bool Record::operator<=(const Record& rhs) {
  return score <= rhs.score;
}

Note, if you define < and <=, you should also probably define the other comparison operators >, >=, ==, and !=. You should also enforce a strict weak ordering (e.g. a < b, b < c implies a < c).

Then to sort descending, you could use the following...

std::sort(records.begin(), records.end(), 
  [] (const Record& lhs, const Record& rhs) -> bool { return lhs > rhs; });

回答2:

To sort a vector of objects

You could overload a comparison operator >¹ for your class, which will look something like:

bool operator> (const Record& r1, const Record& r2) {
    return r1.score > r2.score;
}

or as a member function:

bool Record::operator> (const Record& r) {
     return score > r.score;
}

which will be implicitly substituted as a third parameter in:

std::sort(records.begin(), records.end(), overloaded_comparison_operator)

You could also use a lambda function directly in sort:

std::sort(records.begin(), records.end(), [](const Record & r1,const Record & r2) -> bool {
                                          return r1.score > r2.score; });

^{1. You could use any of the comparison operators you find useful in your case. Bear in mind operator < will sort in ascending, while operator > in descending order.}

来源：https://stackoverflow.com/questions/34385586/sort-vector-of-class-objects-based-on-some-member-variable

标签

class

sorting

vector