def transform(self, fn, dtype=None, *args, **kwargs):
        """Equivalent to map, compatibility purpose only.
        Column parameter ignored.
        """
        rdd = self._rdd.map(fn)

        if dtype is None:
            return self.__class__(rdd, noblock=True, **self.get_params())
        if dtype is np.ndarray:
            return ArrayRDD(rdd, bsize=self.bsize, noblock=True)
        elif dtype is sp.spmatrix:
            return SparseRDD(rdd, bsize=self.bsize, noblock=True)
        else:
            return BlockRDD(rdd, bsize=self.bsize, dtype=dtype, noblock=True)
Equivalent to map, compatibility purpose only.
        Column parameter ignored.