code: def currentGrouping( self ):
          
          groupBy = self.groupBy()
          if ( groupBy == XOrbBrowserWidget.GroupByAdvancedKey ):
              return self.advancedGrouping()
          else:
              table = self.tableType()
              if ( not table ):
                  return []
              
              for column in table.schema().columns():
                  if ( column.displayName() == groupBy ):
                      return [column.name()]
              
              return []
docs: Returns the current grouping for this widget.
          
          :return     [<str> group level, ..]