使用linq分组后查找平均和最大时间

给定以下类别:

public class SessionData
{
    public Guid Session { get; set; }
    public DateTime Date { get; set; }
}

public static List<SessionData> GetSessionData()
{
    Guid guid1 = Guid.NewGuid();
    Guid guid2 = Guid.NewGuid();

    List<SessionData> sessionData = new List<SessionData>
    {
        new SessionData {Session = guid1, Date = DateTime.UtcNow.AddMinutes(3)},
        new SessionData {Session = guid1, Date = DateTime.UtcNow.AddMinutes(2)},
        new SessionData {Session = guid2, Date = DateTime.UtcNow.AddMinutes(5)},
        new SessionData {Session = guid2, Date = DateTime.UtcNow.AddMinutes(4)},
        new SessionData {Session = guid1, Date = DateTime.UtcNow.AddMinutes(20)},
        new SessionData {Session = guid1, Date = DateTime.UtcNow.AddMinutes(25)},
        new SessionData {Session = guid2, Date = DateTime.UtcNow.AddMinutes(20)},
        new SessionData {Session = guid1, Date = DateTime.UtcNow.AddMinutes(1)},
    };

    return sessionData;
}

我想找出会话的平均持续时间(1)和最长会话(2)。还有,每天(3)、每周(4)、每月(5)、年(6)总共(7)有多少个疗程?

我试着从

var list = (from t in sessionData group t.Date by t.Session).ToList();