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I have two Map[String, T]s, where T is an instance of subtype of Fruit. I need to construct new Map from two Maps, where the key is the common key names from the two maps, and the value is the Seq[Fruit] iff the values from the two maps shares the same type.

class Fruit case class Apple() extends Fruit case class Banana(num: Int) extends Fruit case class Orange() extends Fruit

For example, if I have following two maps:

val map1 = Map("first" -> Apple(), "second" -> Banana(3), "third" -> Orange()) val map2 = Map("first" -> Orange(), "second" -> Banana(4), "third" -> Orange())

I need the result map, map3 which has following members:

generateMap(map1: Map[String, Fruit], map2: Map[String, Fruit]): Map[String, Seq[Fruit]] => results a map look like Map("second" -> Seq(Banana(3), Banana(4)), "third" -> Seq(Orange(), Orange())

I'm not sure how to write a function, generateMap. Could anyone help me to implement that? (using Scala 2.11.x)

Note that the class definitions (Fruits and others) are fixed, so I cannot modify them.

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scala> val r: Map[String, Seq[Fruit]] = (map1.toList ++ map2.toList). groupBy(x => x._1). mapValues(lst => lst.map(x => x._2)). .filter { case (key, lst) => lst.forall(x => x.getClass == lst.head.getClass) } r: Map[String, Seq[Fruit]] = Map(third -> List(Orange(), Orange()), second -> List(Banana(3), Banana(4)))
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thanks, but the result is different from what I expected. Because the map1("first") has the different type from map2("first"), the generated output should not have "first".
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val m3 = (map1.toSeq ++ map2.toSeq). // Combine the maps groupBy (x=>x._1). //Group by the original keys map{case (k,lst)=> (k, lst.map(x=> x._2))}. //Strip the keys from the grouped sequences filter{case (_, lst) => lst.forall(i => lst.head.getClass == i.getClass)}. //Filter out hetergeneous seqs toMap // Make a map

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Without forall:

(map1.toList ++ map2.toList).groupBy(_._1).mapValues(_.map(_._2)) .filter(_._2.map(_.getClass).toSet.tail.isEmpty) Map(third -> List(Orange(), Orange()), second -> List(Banana(3), Banana(4)))

This version requires a little more (but still linear inside filter) CPU and memory than version with forall, so you should use it only for small collections.

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