VB.NET GroupBy LINQ statement

Question

I am having a bear of a time getting this to work. I have a List(Of MyItem) called Items that have a OrderId property on them. From those items, I want to create a list of Orders. Some items will have the same OrderId so I want to try to group by OrderId. I then want to sort by date. Here's what I have so far:

Public ReadOnly Property AllOrders() As List(Of Order)
    Get
         Return Items.Select(Function(i As MyItem) New Order(i.OrderID)) _
         .GroupBy(Function(o As Order) New Order(o.OrderID)) _
         .OrderBy(Function(o As Order) o.DateOrdered).ToList
    End Get
End Property

This, of course, doesn't compile, and I get the error:

Value of type 'System.Collections.Generic.List(Of System.Linq.IGrouping(Of Order, Order))' cannot be converted to 'System.Collections.Generic.List(Of Order))'

I've bolded the part where I think the problem is, but I have no idea how to fix it. Also, it used to work fine (except there were duplicate values) before I added the .GroupBy statement. Anyone have any ideas?

Thanks

EDIT

Basically, I want this:

List of Existing Items      Take List and Turn it into 
List(Of MyItem):                 List(Of Order):
ItemId  OrderId                    OrderID 
1       100                        100
2       102                        102
3       100

Answer 1

By putting the OrderBy after the GroupBy, you are instructing it to sort the groups. A group of Orders doesn't have a single date. I'm thinking what you probably want to do is switch the OrderBy and GroupBy around; unless GroupBy loses any prior sort order, in which case you'll have to sort each Group.

This also looks wrong to me

.GroupBy(Function(o As Order) New Order(o.OrderID))

Should it not be

.GroupBy(Function(o As Order) o.OrderID)

Answer 2

I said F it and used some less pretty code:

Public ReadOnly Property AllOrders() As List(Of Order)
    Get
        Dim ids = Items.Select(Function(i As OrderItem) i.OrderID).Distinct()
        Dim orders As New List(Of Order)
        For Each i As Integer In ids
            orders.Add(New Order(i))
        Next
        Return orders.OrderBy(Function(o As Order) o.DateOrdered).ToList
    End Get
End Property

If anyone has a LINQier way of doing it, I would prefer to do it that way. Otherwise, I guess this piece of kludge will have to do.

Answer 3

You don't need to use group by for this.

Public ReadOnly Property AllOrders() As List(Of Order)
Get
     Return Items.Select(Function(i) i.OrderID).Distinct.Select(Function(p) New Order(p)).ToList()
End Get
End Property

If you want to order it by the OrderedDate on the order, just add an orderby clause before the ToList

Public ReadOnly Property AllOrders() As List(Of Order)
Get
     Return Items.Select(Function(i) i.OrderID).Distinct _
                 .Select(Function(p) New Order(p)) _
                 .OrderBy(Function(s) s.DateOrdered).ToList()
End Get
End Property