LINQ group by Count and Avarage/avg

var query = from q in this.context.TRAINING_PLAYER
                        group q by q.session_id into grp
                        select new
                        {
                            sessionId = grp.Key,
                            count = grp.Select(p => p.player_id).Distinct().Count()
                        };

            var mean = query.Average(p => p.count);