CODEWITHSUNDEEP
scaladictionary
WestCoastProjects
WestCoastProjects

Reputation: 63022

Scala: how to destructure a basic map entry

Here is a vanilla scala map:

scala> val m = Map( 'a'-> '1', 'b' -> 2)
m: scala.collection.immutable.Map[Char,AnyVal] = Map(a -> 1, b -> 2)

The Map iterator() method returns a tuple representing the (key,value). So if we want to see, say, just the values of the map we can do this:

scala> m.map( a => a._2)
res0: scala.collection.immutable.Iterable[AnyVal] = List(1, 2)

But how do we destructure the map entry ? The following does not work:

scala> m.map( (a,b) =>  b)
<console>:10: error: wrong number of parameters; expected = 1
              m.map( (a,b) =>  b)
                       ^

Upvotes: 5

Views: 2091

Answers (2)

senia
senia

Reputation: 38045

You should use pattern matching:

m.map{ case (a, b) =>  b}

Map entry is just a Tuple2.

Upvotes: 7

kiritsuku
kiritsuku

Reputation: 53348

Just in case you don't want to write the case {...} syntax:

scala> import Function.{ tupled => $ }
import Function.{tupled=>$}

scala> Map(1 -> "a") map $((a,b) => b)
res1: scala.collection.immutable.Iterable[String] = List(a)

scala> Map(1 -> "a") map $((a,b) => a -> s"$b!")
res2: scala.collection.immutable.Map[Int,String] = Map(1 -> a!)

Upvotes: 4

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