Flattens the grouped data structure.

        #TODO: The parameters here are meaningless

        Flattens the grouped data structure.
        What is returned is a DataFrameWeld object.

def reset_index(self, inplace=True, drop=True):
        """ Flattens the grouped data structure.

        #TODO: The parameters here are meaningless

        Flattens the grouped data structure.
        What is returned is a DataFrameWeld object.
        """
        if len(self.column_types) == 1:
            vectype = self.column_types[0]
            if isinstance(vectype, WeldVec):
                elem_type = vectype.elemType
                if isinstance(elem_type, WeldStruct):
                    self.column_types = elem_type.field_types
                    value_type = WeldStruct(self.column_types)
                else:
                    self.column_types = elem_type
                    value_type = elem_type
                if len(self.grouping_column_types) == 1:
                    group_type = self.grouping_column_types[0]
                else:
                    group_type = WeldStruct(self.grouping_column_types)

                self.weld_type = WeldStruct([group_type, value_type])
                self.expr = grizzly_impl.flatten_group(
                    self.expr,
                    self.column_types,
                    self.grouping_column_types
                )