Depois de:

val df = Seq((1, Vector(2, 3, 4)), (1, Vector(2, 3, 4))).toDF("Col1", "Col2")

Eu tenho esse DataFrame no Apache Spark:

+------+---------+
| Col1 | Col2    |
+------+---------+
|  1   |[2, 3, 4]|
|  1   |[2, 3, 4]|
+------+---------+

Como faço para converter isso em:

+------+------+------+------+
| Col1 | Col2 | Col3 | Col4 |
+------+------+------+------+
|  1   |  2   |  3   |  4   |
|  1   |  2   |  3   |  4   |
+------+------+------+------+