LINQ : groups within groups

            
var groupsByType = (from SPListItem n in notifications
                    group n by n[C.DPRequestsQueueNotifications.NotificationType] into groupByType
                    let groupsBySubject = from n in groupByType
                                  group n by n[C.DPRequestsQueueNotifications.Title] into groupBySubject
                                  select groupBySubject
                    select groupsBySubject).ToList();

foreach (var groupByType in groupsByType)
{
    foreach (var groupBySubject in groupByType)
    {
        foreach (SPListItem item in groupBySubject)
        {
            // TODO
        }
    }
}