code: def coalesce(self):
          
          self.known = self.known.coalesce()
          self.active = self.active.coalesce()
          self.active = (self.known & self.active).coalesce()
          return self
docs: Coalesce the segments for this flag.
  
          This method does two things:
  
          - `coalesces <SegmentList.coalesce>` the `~DataQualityFlag.known` and
            `~DataQualityFlag.active` segment lists
          - forces the `active` segments to be a proper subset of the `known`
            segments
  
          .. note::
  
              this operations is performed in-place.
  
          Returns
          -------
          self
              a view of this flag, not a copy.