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

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