Snippet9

  // map function returns a tuple of (1, Age)
  edge => edge.sendToDst(1, edge.srcAttr.age.toDouble),
  // reduce function combines (sumOfFollowers, sumOfAge)
  (a, b) => ((a._1 + b._1), (a._2 + b._2))
  ).mapValues((id, p) => p._2 / p._1)