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I have an array of ListViewItems ( ListViewItem[] ), where I store a SalesOrderMaster object in each ListViewItem.Tag for later reference. I have some code that right now, goes through each ListViewItem safely casts the .Tag property into a SalesOrderMaster object, then adds that object to a collection of SalesOrders, only after checking to make sure the order doesn't already exist in that collection. The process to compare sales orders is expensive, and I would like to convert this to a LINQ expression for clarity and performance. ( I also have the Parallel Extensions to .NET Framework 3.5 installed so I can use that to further improve LINQ performance) So without further ado: This is what I have, and then what I want. ( what I want won't compile, so I know I am doing something wrong, but I hope it illustrates the point ) What I have: ( Slow ) foreach (ListViewItem item in e.Argument as ListViewItem[]) { SalesOrderMaster order = item.Tag as SalesOrderMaster; if ( order == null ) { return; } if (!All_SalesOrders.Contains(order)) { All_SalesOrders.Add(order); } } What I want: ( Theory ) List<SalesOrderMaster> orders = (from item in (e.Argument as ListViewItem[]).AsParallel() select new { ((SalesOrderMaster)item.Tag) }).Distinct(); EDIT: I know the cast is cheap, I said the "Compare", which in this case translates to the .Contains(order) operation EDIT: Everyone's answer was awesome! I wish I could mark more than one answer, but in the end I have to pick one. EDIT : This

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