Efficient way to remove duplicates - c++

Question

Following the answer in this thread "What's the most efficient way to erase duplicates and sort a vector?". I wrote the following code, but I got an error complaing no match for ‘operator<’ (operand types are ‘const connector’ and ‘const connector’) blahblah...
connector is a class I wrote myself, it basically is a line with two geometry points. uniqCntrs is a std::vector. It has 100% duplicates in it, which means each element has a duplicate, the size of uniqCntrs is quite big. What's wrong with my code, and how to deal with this situation?
std::set<connector> uniqCntrsSet;
for(unsigned int i = 0; i < uniqCntrs.size(); ++i )
{
uniqCntrsSet.insert(uniqCntrs[i]);
}
uniqCntrs.assign(uniqCntrsSet.begin(), uniqCntrsSet.end());
Edit:
I have no idea how to define < operator for my connector class. I mean it is physically meaningless to say one line is smaller than the other.

Answer 1

From cppreference:
std::set is an associative container that contains a sorted set of unique objects of type Key. Sorting is done using the key comparison function Compare.
The second template argument of std::set, Compare, is defaulted to std::less which by defaults compares the objects with operator<. To fix the issue you can simply define operator< for your Key type (connector that is).

Answer 2

Actually the operator< is just used to efficiently order the map which is used by std::set. It does not need to make any sense. The only requirement is that the operator satisfy the standard mathematical definition of a strict weak ordering.
Look at this point example:
class Point
{
public:
Point(int x, int y) : x(x), y(y) {
}
public:
bool operator==(const Point &other) const {
return x==other.x && y==other.y;
}
bool operator!=(const Point &other) const {
return !operator==(other);
}
bool operator<(const Point &other) const {
if (x==other.x) {
return y<other.y;
} else {
return x<other.x;
}
}
private:
int x;
int y;
};