def unstack(self):
        """
        Unstack array and return a new BoltArraySpark via flatMap().
        """
        from bolt.spark.array import BoltArraySpark

        if self._rekeyed:
            rdd = self._rdd
        else:
            rdd = self._rdd.flatMap(lambda kv: zip(kv[0], list(kv[1])))

        return BoltArraySpark(rdd, shape=self.shape, split=self.split)