code: def interactions_per_contact(records, direction=None):
      
      if direction is None:
          counter = Counter(r.correspondent_id for r in records)
      else:
          counter = Counter(r.correspondent_id for r in records
                            if r.direction == direction)
      return summary_stats(counter.values())
docs: The number of interactions a user had with each of its contacts.
  
      Parameters
      ----------
      direction : str, optional
          Filters the records by their direction: ``None`` for all records,
          ``'in'`` for incoming, and ``'out'`` for outgoing.