def size(self):
        """Returns the sizes of the groups as series.

        Returns:
            TYPE: Description
        """
        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
        )
Returns the sizes of the groups as series.

        Returns:
            TYPE: Description