'Counts the number of aggregated activities which are unseen
:param aggregated_activities: allows you to specify the aggregated
activities for improved performance'

def count_unseen(self, aggregated_activities=None):

    count = 0
    if (aggregated_activities is None):
        aggregated_activities = self[:self.max_length]
    for aggregated in aggregated_activities:
        if (not aggregated.is_seen()):
            count += 1
    return count
