code: def size(self):
          
          if len(self.grouping_column_types) > 1:
              index_type = WeldStruct([self.grouping_column_types])
              # Figure out what to use for multi-key index name
              # index_name = ??
          else:
              index_type = self.grouping_column_types[0]
              index_name = self.grouping_column_names[0]
          return SeriesWeld(
              grizzly_impl.groupby_size(
                  self.columns,
                  self.column_types,
                  self.grouping_columns,
                  self.grouping_column_types
              ),
              WeldLong(),
              index_type=index_type,
              index_name=index_name
          )
docs: Returns the sizes of the groups as series.
  
          Returns:
              TYPE: Description