How to sort a multidimensional vector of floats? - c++

Question

So, I have a set of points in 3D, and I would like to store them in a 3 dimensional vector. Then I need sort that vector, giving priority first to the X dimention, then Y, then Z. So, for example, if I have this set of points:
P1 = (5, 10 ,9)
P2 = (1, 11, 4)
P3 = (8, 5, 2)
P4 = (5, 10, 3)
P5 = (5, 4, 0)
I would like to get a vector sorted like this:
[1, 11, 4]
[5, 4, 0]
[5, 10, 3]
[5, 10, 9]
[8, 5, 2]
So, how can a sort a multidimentional vector taking all rows into account?
Should I use std::priority_queue instead? If so, how show I use it?
Thanks

Answer 1

You could use an std::tuple<double, double, double> to represent a point. The comparison for std::tuple works lexicographically, the way you want it to. Alternatively, you could provide a custom sort function to your vector of points. Something like this:
sort(pointVector.begin(), pointVector.end(), [](const Point& lhs, const Point& rhs){//Implement your required comparison predicate here});
Also, as this question shows, you can achieve some sort of a named-tuple-with-lexicographic-sorting by using std::tuples lexicographic sort and std::tie.

Answer 2

...giving priority first to the X dimention, then Y, then Z
Use std::sort with std::tie, something like following
#include <algorithm>
#include <tuple>
//....
struct Points // Your 3D Point
{
float x,y,z;
} ;
std::vector<Points> v; // Vector of 3D points
std::sort( v.begin(), v.end(),
[]( const Points& lhs, const Points& rhs )
{
return std::tie(lhs.x,lhs.y,lhs.z)
< std::tie(rhs.x,rhs.y,rhs.z) ;
}
) ;
DEMO

Answer 3

You can use the std::sort() to easily sort according to your specific conditions by making your own comparator function.
Assuming you have stored a single 3D point in a struct point, and the points in a std::vector<points> (A std::tuple might be more useful.), try out this code.
Example:
#include <vector>
#include <algorithm>
using namespace std;
struct point
{
float x, y, z;
}
bool mySort(const point& a, const point& b)
{
//A naive comparison to help you understand better.
//You could always use std::tie for lexicographical comparison.
if (a.x == b.x)
{
if (a.y == b.y)
return a.z < b.z;
else
return a.y < b.y;
}
else
return a.x < b.x;
}
int main()
{
vector<point> graph;
//push_back() all your points into the graph.
//mySort() is a custom comparator function.
sort(graph.begin(),graph.end(),mySort);
}