def modify(self, clazz, new_col, *args):
if is_callable(clazz) and not is_none(new_col) and has_elements(*args):<EOL><INDENT>return self.__do_modify(clazz, new_col, *args)<EOL><DEDENT>
Modify some columns (i.e. apply a function) and add the
result to the table.

:param clazz: name of a class that extends class Callable
:type clazz: class
:param new_col: name of the new column
:type new_col: str
:param args: list of column names of the object that
function should be applied to
:type args: tuple
:return: returns a new dataframe object with the modiefied values,
 i.e. the new column
:rtype: DataFrame