CODEWITHSUNDEEP
scalalist
Pratham Solanki
Pratham Solanki

Reputation: 347

How to join (FULL OUTER) two Lists in Scala?

I have two Lists: dec_tyres and jan_tyres:

scala> dec_tyres
res21: List[(String, Int)] = List((007139::21,10), .....

scala> jan_tyres
res22: List[(String, Int)] = List((005179::24,2), ..... 

scala> dec_tyres.length
res19: Int = 71

scala> jan_tyres.length
res20: Int = 82

Now to join these I'm doing:

val mb = jan_tyres.toMap
val tyres_count = dec_tyres.flatMap{case (ka,va) => mb.get(ka).map(vb => (ka,va,vb))}.toList

Which gives me:

scala> tyres_count
res23: List[(String, Int, Int)] = List((007139::21,10,8), .....

scala> tyres_count.length
res24: Int = 53

This is computing an inner join and giving me only 53 records, where I'm expecting 100 records.

All the records where both of the dec_tyres and jan_tyres do not have a common key are scraped. Instead I want that record with the particular key instead a zero as the respective value.

The solution is hence a "Full Outer Join", which I'm really struggling with.

Upvotes: 1

Views: 1977

Answers (1)

jwvh
jwvh

Reputation: 51271

So you want a (String, Int, Int) result for every unique String from the two (String, Int) input lists?

val janMap = jan_tyres.toMap  // for fast lookup
val decMap = dec_tyres.toMap

val tyres_count = (jan_tyres ++ dec_tyres).map(_._1).distinct.map{ k =>
  (k, decMap.getOrElse(k, 0), janMap.getOrElse(k, 0))
}

Combine the lists (++), keep only the key strings (map(_._1)), remove duplicates (distinct), change each key (k) into a tuple using the Maps to retrieve the Int values (map{...}).

Upvotes: 3

Related Questions