def weight_field(self, f):
        """
        Select one field as the weight field.

        Note that this field will be exclude from feature fields.

        :param f: Selected weight field
        :type f: str
        :rtype: DataFrame
        """
        if f is None:
            raise ValueError("Field name cannot be None.")
        self._assert_ml_fields_valid(f)
        return _change_singleton_roles(self, {f: FieldRole.WEIGHT}, clear_feature=True)