fold(zeroValue: T, op: Callable[[T, T], T]) → T¶
Aggregate the elements of each partition, and then the results for all the partitions, using a given associative function and a neutral “zero value.”
op(t1, t2)is allowed to modify
t1and return it as its result value to avoid object allocation; however, it should not modify
This behaves somewhat differently from fold operations implemented for non-distributed collections in functional languages like Scala. This fold operation may be applied to partitions individually, and then fold those results into the final result, rather than apply the fold to each element sequentially in some defined ordering. For functions that are not commutative, the result may differ from that of a fold applied to a non-distributed collection.
>>> from operator import add >>> sc.parallelize([1, 2, 3, 4, 5]).fold(0, add) 15