code: def _filter_group(self, group):
          
          self.metadata = [x for x in self.metadata if x.group == group]
          group_set = set([x.id for x in self.metadata])
          self.objects = [obj for obj in self.objects if id(obj) in group_set]
          self.count = len(self.metadata)
          if self.metadata == []:
              return False
  
          self.edges = [e for e in self.edges if e.group == group]
  
          del self._max_group
  
          return True
docs: Eliminate all objects but those which belong to `group`.
          ``self.objects``, ``self.metadata`` and ``self.edges`` are modified.
          Returns `True` if the group is non-empty. Otherwise returns `False`.