@SuppressWarnings("unchecked")
@Test
public void persist() {
JavaDoubleRDD doubleRDD = sc.parallelizeDoubles(Arrays.asList(1.0, 1.0, 2.0, 3.0, 5.0, 8.0));
doubleRDD = doubleRDD.persist(StorageLevel.DISK_ONLY());
Assert.assertEquals(20, doubleRDD.sum(), 0.1);
List<Tuple2<Integer, String>> pairs = Arrays.asList(
new Tuple2<Integer, String>(1, "a"),
new Tuple2<Integer, String>(2, "aa"),