Indices of sentences when enumerating data set from batches.
        Useful when retrieving the correct order of sentences

        Returns
        -------
        list
            List of ids ranging from 0 to #sent -1

def idx_sequence(self):
        """Indices of sentences when enumerating data set from batches.
        Useful when retrieving the correct order of sentences

        Returns
        -------
        list
            List of ids ranging from 0 to #sent -1
        """
        return [x[1] for x in sorted(zip(self._record, list(range(len(self._record)))))]