Question

I have a class

public class Entity : IComparable<Entity>
{

    public float Priority { get; set; }

{

I create a list and fill it with Y items that are in no particular order

list <Entity> = get_unorderd_list();

now i want to sort the list according to the Priority value , but I only care about getting the highest X items in the right order, for performance reasons I don’t want to use a regular .sort() method as X is a lot smaller then Y.

Should I write a custom sorting method? Or is there a way to do this?

edit:not talking about geting a single velue by using .max()

Answer 1

Should I write a custom sorting method?

I don’t know of a way of doing it easily from .NET itself. When I implemented sorting for Edulinq, I took this sort of approach – the whole ordering is a quick-sort, but I only sort as much as I need to in order to return the results so far.

Now, that’s still a general approach – if you know how many results you need beforehand, you can probably do a lot better. You might want to build a heap-based solution, where you have a bounded heap (max size X) and then iterate over your input, adding values into your heap as you go. As soon as you’ve filled up the first X elements, you can start discarding new ones which are smaller than your smallest heap element, without even looking at the rest of the tree. For other elements, you perform the normal operations to insert the element, maintaining the ordering within the heap.

See the Wikipedia article on binary heaps stored as arrays for more information about how you might structure your heap.