group by multiple columns in linq to sql

Today's I have a requirement to group multiple columns in linq to sql which are given below.

The below UserUsage table have AParty_Subscriber, ProductService, NetworkID and Unit columns.

I am going to filter UserUsage table using group by multiple columns. i.e.

List<UserUsage> userUsages = (from a in use

                                            group a by new {

                                                        a.AParty_Subscriber,

                                                        a.ProductService

                                             }

                                into b select new UserUsage {

                                              AParty_Subscriber = b.Key.AParty_Subscriber,

                                              ProductService = b.Max(a => a.ProductService),

                                              NetworkID = b.Max(a => a.NetworkID),

                                              Unit = b.Sum(a => int.Parse(a.Unit)).ToString()

                                }).ToList();