val orders = sc.textFile("/public/retail_db/orders")
val ordersMap = orders.
  map(o => (o.split(",")(0).toInt, o))

val orderItems = sc.textFile("/public/retail_db/order_items")
val orderItemsMap = orderItems.
  map(oi => (oi.split(",")(1).toInt, oi))

val ordersLeftOuterJoin = ordersMap.
  leftOuterJoin(orderItemsMap)

ordersLeftOuterJoin.
  filter(o => o._2._2 == None).
  take(100).
  foreach(println)

ordersLeftOuterJoin.
  filter(o => o._2._2 == None).
  count