OrderBy().ThenBy() wrong output

Question

I have a list of Points with 50 elements, I wanted to sort them so I used orderby thenby to, but my output seems to be wrong. The first elements are sorted in accordingly, but the next ones are wrong, here is a screen shot.

The 1st five data where sorted correctly, that should be what the other data would be. but the next ones are not. I don't know what is the problem.

So the next five output must be:

{X=249, Y=198}

{X=249, Y=308}

{X=249, Y=413}

{X=249, Y=519}

{X=249, Y=629}

My list is a PointF list:

List<PointF> points = new List<PointF>();

Here is my code:

points = points.OrderBy(c => c.X).ThenBy(c => c.Y).ToList();

Answer 1

Please verify that your points' X values are indeed equal. I assume both 249 and 249.000001 may get rendered as "249" in a listbox, but will not be equal for the ordering purposes.

I suggest changing your code to

points = points.OrderBy(c => Math.Round(c.X)).ThenBy(c => c.Y).ToList();

and seeing if the problem is gone.

UPDATE: if your coordinates are expected to be non-integers, switch to comparing with specified precision:

var precision = 0.001; // choose the value that suits you. If the tow values are different by less than this amount, the values are considered equal.
points = points.OrderBy(c => Math.Round(c.X / precision)).ThenBy(c => c.Y).ToList();

Also, instead of using Round(c.X) you could use (int)c.X, since your comments indicate that this is how you output your values to the listbox.