How to sort the coordinates of a hash set in C#

Question

I'm saving coordinate values in the HashSet.

And I want to sort it in order in the picture above.

Below is a typical point structure, using a Hashset.

struct Point
{
    public int x, y;
    public Point(int x, int y)
    {
        this.x = x;
        this.y = y;
    }
}

private HashSet<Point> hashset = new HashSet<Point>();

I found a source that just sort one value.

However, i have not found a source that sort two or coordinates values.

Give me an example of how to sort the coordinates.

How do you want points within a given quadrant to be ordered? — Roger Lipscombe, May 07 '19 at 12:02
HashSets have no order, which means it doesn't matter whether you use a HashSet or an array to store the values. Do you want to *store* the values in a specific sort order (in which case you'll have to use a different container) or read them in a specific order? In that case you could use LINQ and any container that allows sorting with `Comparer` argument, and use a custom comparer — Panagiotis Kanavos, May 07 '19 at 12:06
and for a set that conserve order https://stackoverflow.com/questions/1552225/hashset-that-preserves-ordering — xdtTransform, May 07 '19 at 12:42
Actually HashSet does have an order since you can use it as IEnumerable and it does maintain order in reality, but it's not a behaviour that one can depend on since it's not guaranteed and of course it's not a good idea anyway to do that :) — Ilya Chernomordik, May 07 '19 at 13:30
@IlyaChernomordik But is unlikely to be insertion order and will possibly be completely different after adding an item. — spender, May 07 '19 at 18:07
I think it actually is, at least looked like that in my examples, but it's of course just a curiosity not a call to action :) — Ilya Chernomordik, May 07 '19 at 19:28

Ilya Chernomordik · Answer 1 · 2019-05-07T12:19:37.303

You can use custom comparer to achieve what you want, where you can define your own rules:

var comparer = Comparer<Point>.Create((p1, p2) =>
{
    if (p1.y < p2.y)
    {
       return p1.x > p2.x ? 1 : -1;
    } 
    else
    {
       return p1.x < p2.x ? 1 : -1;
    }
});

hashset.OrderBy(p => p, comparer)

P.S. Not 100% sure that all the conditions are correct, but you get the idea I hope, so that you can write the logic you want following this example.

spender · Answer 2 · 2019-05-07T12:45:38.383

1

points.OrderBy(p => Math.Atan2(p.y, p.x))

should do the trick.

It will order the points by their direction, measured from origin (i.e. starting from "west" in a clockwise direction)

If you're hoping to maintain that order in a set based structure, you'll need to think again because HashSet<T> has no implicit ordering.

edited May 07 '19 at 12:45

answered May 07 '19 at 12:30

spender

117,338
33
229
351

How to sort the coordinates of a hash set in C#

2 Answers2