class obj { int typeId; //10 types 0-9 string uniqueString; //this is unique }
Assume there is list with 100 elements of obj, but only 10
Sure, use Enumerable.Distinct.
Given a collection of obj (e.g. foo), you'd do something like this:
obj
foo
var distinctTypeIDs = foo.Select(x => x.typeID).Distinct();