How should I extract a collection of distinct values from a List<T> of custom objects?

I've got a List of objects - let's say they're Orders.

Order

OrderID

Date

SalesmanId

...

I want to extract a Distinct list of SalesmanIds from this list. What is the best way to do this? I don't suppose its looping through manually ... is it?

UPDATE Thanks for your responses. I've thought o开发者_如何转开发f an extra requirement (outlined after Jon Skeets answer) and coded it like this:

var salesusers = from s in lstOrders 
                 group s by new { s.SalesUserId,s.Username} 
                 into g  
                 select new { UserName = g.Key.Username, UserId = g.Key.SalesUserId };

It works, but I'm not sure if this is the right sort of approach or if I'm way off the mark?

Thanks.

UPDATE #2: This one ran and ran - newbies like me might find answers to this linked question useful too.

If you only need to get the SalesmanIds, it's easy:

var salesmanIds = orders.Select(x => x.SalesmanId)
                        .Distinct();

Call ToList() if you need it as a List<T>.

You need a using directive for System.Linq.

EDIT: Okay, to get both the name and ID, you can use:

var salesmanIds = orders.Select(x => new { x.SalesmanId, x.UserName })
                        .Distinct();

I'd prefer this way:

Implement the IEqualityComparer<T> interface for Order (just so you can properly compare them.

Then just do:

IEnumerable<Order> myDistinctOrders = oredersList.Distinct();