LINQ: Order By Count of Unique Items in List<string>
List<string> aryIDs = new List<string>();aryIDs.Add("1234");aryIDs.Add("4321");aryIDs.Add("3214");aryIDs.Add("1234");aryIDs.Add("4321");aryIDs.Add("1234"); var result = from id in aryIDsgroup id by id into gorderby g.Count() descendingselect new { Id=g.Key, Count=g.Count() };result.Dump();Cut and paste that into LinqPad and you should be good to go.
It could also be written using Lambda expressions as:
aryIDs.GroupBy (id => id).OrderByDescending (id => id.Count()).Select(g => new { Id=g.Key, Count=g.Count()}).Dump();
How about http://msdn.microsoft.com/en-us/vcsharp/aa336747#countGrouped:
List<Customer> customers = GetCustomerList();var orderCounts = from c in customers select new { c.CustomerID, OrderCount = c.Orders.Count() };