def rename(self, data, variables=None):
if variables is None:<EOL><INDENT>variables = self.variables<EOL><DEDENT>return data.rename(columns={y: x for x, y in variables.items()})<EOL>
Renames the columns according the variable mapping.

Parameters
----------
data: DataFrame
variables: None or dict, default None
    If None, uses self.variables

Returns
-------
data: DataFrame
    Renamed data.