def __call__(self, head: RDD):
if self.head is None or self.trace != self.path():
self.head = head.persist(self.persistence)
self.trace = self.path()
return self.head
def materialize(rdd: RDD):
rdd.persist(STORAGE_LEVEL)
rdd.mapPartitionsWithIndex(lambda ind, it: (1, )).collect()
return rdd
