in src/main/scala/com/spotify/bdrc/pipeline/Statistics.scala [69:76]
def scioAlgebird(input: SCollection[Rating]): SCollection[Stats] =
input.aggregate(aggregator)
// ## Spark
def spark(input: RDD[Rating]): Stats = {
val s = input.map(_.score).stats()
Stats(s.max, s.min, s.sum, s.count, s.mean, s.stdev)
}