cjauvin

val pairs = sc.parallelize(List(("aa", 1), ("bb", 2),
                                ("aa", 10), ("bb", 20),
                                ("aa", 100), ("bb", 200)))

/* aggregateByKey takes an initial accumulator (here an empty list),
   a first lambda function to merge a value to an accumulator, and a
   second lambda function to merge two accumulators */
pairs.aggregateByKey(List[Any]())(
  (aggr, value) => aggr ::: (value :: Nil),
  (aggr1, aggr2) => aggr1 ::: aggr2