Is there a quick and easy way to do a select distinct
You can use GroupBy
:
Pallets = (from o in this.OrdersModel.GroupBy(o => o.PONumber).Select(g => g.First())
where o.Pallets != null
select double.Parse(o.Pallets))
.Sum();
But you should probably try to fix your model so you don't get duplicate records in the first place!