Question

This is related to this question

I have a vector of points that will, for instance, store 100K+ points.

std::vector<Point> point_vec; 

I want to check if a position (x, y, z) to be added is already in point_vec (represented by an instance of class Point ). The following function will check this (in a for loop)

bool samePoints(const Point& p1, 
                const double x1, 
                const double y1, 
                const double z1) {

     return fabs(p1.x - x1) < EPSILON &&
            fabs(p1.y - y1) < EPSILON &&
            fabs(p1.z - z1) < EPSILON;
}

But, I guess checking if x in list/ vector will be a costly operation. I want to know if there is a better way to check if a) Points are equal (perhaps an operator “=” on class Point?? and (b) Is there some other , better data structure than `vector’ that I should make use of. OR if there is an operation on vector that will speed up checking for ‘same points’

For (b) please note that I need to std::sort these points as well. So any other data structure that you may suggest should be able to sort these points.

UPDATE

I want the points in the sorted state only. It is just that vector doesn’t sort those (so I need to perform a sort operation. Should I use std::set<Point> point_set instead of instead of std::vector <Point> point_vec ? IF SO: Is adding each point to a set a costly operation ? Or ‘vector’ sorting that I do in the end turns out costlier overall?

Answer 1

Is the collection of points always sorted or must it sometimes be in an unsorted state? If the former, a std:;set of points will be fast to determine if a point is already there, and will maintain the points in sorted order. You would have to supply a suitable ordering function (not an equality one), which may be faster than your equality test.