val orderCustomers1 = sc.textFile("/public/retail_db/orders").
  filter(o => o.split(",")(1).contains("2013-08")).
  map(o => o.split(",")(2).toInt)

val orderCustomers2 = sc.textFile("/public/retail_db/orders").
  filter(o => o.split(",")(1).contains("2013-09")).
  map(o => o.split(",")(2).toInt)

orderCustomers1.count
orderCustomers2.count

orderCustomers1.
  intersection(orderCustomers2).
  take(10).
  foreach(println)

orderCustomers1.
  intersection(orderCustomers2).
  count