def filter_examples(self, field_names):
        """Remove unknown words from dataset examples with respect to given field.

        Arguments:
            field_names (list(str)): Within example only the parts with field names in
                field_names will have their unknown words deleted.
        """
        for i, example in enumerate(self.examples):
            for field_name in field_names:
                vocab = set(self.fields[field_name].vocab.stoi)
                text = getattr(example, field_name)
                example_part = [word for word in text if word in vocab]
                setattr(example, field_name, example_part)
            self.examples[i] = example
Remove unknown words from dataset examples with respect to given field.

        Arguments:
            field_names (list(str)): Within example only the parts with field names in
                field_names will have their unknown words deleted.