How to order tuples based on another, referal tuple - scala

Question

The following Iterable can be o size one, two, or (up to) three.
org.apache.spark.rdd.RDD[Iterable[(String, String, String, String, Long)]] = MappedRDD[17] at map at <console>:75
The second element of each tuple can have any of the following values: A, B, C. Each of these values can appear (at most) once.
What I would like to do is sort them based on the following order (B , A , C), and then create a string by concatenating the elements of the 3rd place. If the corresponding tag is missing then concatenate with a blank space: ``. For example:
this:
CompactBuffer((blah,A,val1,blah,blah), (blah,B,val2,blah,blah), (blah,C,val3,blah,blah))
should result in:
val2,val1,val3
this:
CompactBuffer((blah,A,val1,blah,blah), (blah,C,val3,blah,blah))
should result in:
,val1,val3
this:
CompactBuffer((blah,A,val1,blah,blah), (blah,B,val2,blah,blah))
should result in:
val2,val1,
this:
CompactBuffer((blah,B,val2,blah,blah))
should result in:
val2,,
and so on so forth.

Answer 1

In your case when A, B and C appear at most once, you could add the corresponding values to a temporary map and retrieve the values from the map in the correct order.
If we use getOrElse to get the values from the map, we can specify the empty string as default value. This way we still get the correct result if our Iterable doesn't contain all the tuples with A, B and C.
type YourTuple = (String, String, String, String, Long)
def orderTuples(order: List[String])(iter: Iterable[YourTuple]) = {
val orderMap = iter.map { case (_, key, value, _, _) => key -> value }.toMap
order.map(s => orderMap.getOrElse(s, "")).mkString(",")
}
We can use this function as follows :
val a = ("blah","A","val1","blah",1L)
val b = ("blah","B","val2","blah",2L)
val c = ("blah","C","val3","blah",3L)
val order = List("B", "A", "C")
val bacOrder = orderTuples(order) _
bacOrder(Iterable(a, b, c)) // String = val2,val1,val3
bacOrder(Iterable(a, c)) // String = ,val1,val3
bacOrder(Iterable(a, b)) // String = val2,val1,
bacOrder(Iterable(b)) // String = val2,,

Answer 2

def orderTuples(xs: Iterable[(String, String, String, String, String)],
order: (String, String, String) = ("B", "A", "C")) = {
type T = Iterable[(String, String, String, String, String)]
type KV = Iterable[(String, String)]
val ord = List(order._1, order._2, order._3)
def loop(xs: T, acc: KV, vs: Iterable[String] = ord): KV = xs match {
case Nil if vs.isEmpty => acc
case Nil => vs.map((_, ",")) ++: acc
case x :: xs => loop(xs, List((x._2, x._3)) ++: acc, vs.filterNot(_ == x._2))
}
def comp(x: String) = ord.zipWithIndex.toMap.apply(x)
loop(xs, Nil).toList.sortBy(x => comp(x._1)).map(_._2).mkString(",")
}