linq group by

var groupList = (from a in list
                    group a by a.OrderID into g
                    select new C_Ordersbase()
                    {
                        OrderID = g.Key,
                        DealDate = g.Where(x => x.OrderID == g.Key).First().DealDate,
                        TotalPrice = g.Sum(x => x.TotalPrice),
                        OrderState = g.Where(x => x.OrderID == g.Key).First().OrderState,
                    });