Is there a non-unique-key sorted list generic collection in C#?

Question

I'm a bit surprised by System.Collections.Generic.SortedList, in that

1. It requires me to use <key, value> instead of <value>(comparer)
2. It only allows on entry per value

These seem quirky in the way I want to use it (although I'm sure they're just right for other situations). Is there another collection that doesn't have these two characteristics?

Answer 1

I am not sure if this will meet your requirements. But you can sort a normal List. MSDN talks about it, but obviously this requires calling sort.

Answer 2

SortedList<,> is really a map sorted by key, not a list. Bad naming, maybe. But there are ways to emulate what you want, depending on your exact requirements. You could, for example, encapsulate a SortedList<T, int> and have add/remove something like:

// add
int count;
if(list.TryGetValue(value, out count)) list[value] = count+1;
else list[value] = 1;

Ultimately you could use a simple list (List<>) too - it depends what you are doing.

In part, I expect that data-binding etc makes it hard to implement a regular list that sorts immediately - you need to implement a lot of interfaces to get that working, as normally it expects the item you add to stay at the end.

Answer 3

I've tried finding this same thing: basically a list that stays ordered as you add items to it. The closest I've found so far is a SortedSet from Goletas.Collections, which uses an AVL tree implementation:

http://www.goletas.com/solutions/collections/

But this class still requires that each element in the list be unique (hence "Set").

Perhaps this class could be modified to support non-unique items.