public IEnumerable<MySched> Fill()
        {

            return new MySched[] {
                new MySched{ ID = 1, MeetUpdate = "10/10/12", ShippDate = ""},
                new MySched{ ID = 2, MeetUpdate = "", ShippDate = "13/10/12"},
                new MySched{ ID = 4, MeetUpdate = "12/10/12" , ShippDate  =""},
                new MySched{ ID = 3, MeetUpdate = "", ShippDate = "11/10/12"}

            };

        }


 private void btnSort()
        {
            var temp = new List<MySched>();

            foreach (var item in Fill())
            {
                string value = item.MeetUpdate == string.Empty ? item.ShippDate : item.MeetUpdate;
                temp.Add(new MySched
                {
                    ID = item.ID,
                    MeetUpdate = item.MeetUpdate,
                    ShippDate = item.ShippDate,
                    DateToSort = value
                });
            }


            foreach (var item in temp.OrderBy(o => o.DateToSort))
            {
                Console.Write(item.DateToSort);
            }
        }