Projection using ToDictionary()

 List<ATMTaskTypePriorityEntry> taskTypePriorityEntries = _taskTypePriorityDatabaseAccess.GetAllPriorities(transactionArgs);
 TaskTypePriorities = taskTypePriorityEntries
                .GroupBy(entry => entry.TaskTypeDbId)
                .Select(entries => new ATMTaskTypePriorities(entries.Key,
                    entries.ToDictionary(entry => entry.EventThreshold, entry => entry.Priority))).ToList();