Tag: Seq

Scala: Seq, Map and Set as functions

Yesterday my mate asked me: “I have a List[String] and a Map[String, Int] and I want a List[Int] where its values are those of the Map whose keys match the List[String] elements, maintaining the order. Should I use pattern matching?”. I know, the sentence is a bit convoluted but the code will make it clear, hopefully. Anyway, I replied: “No, you don’t need pattern matching, you just need this”:

 
scala> val m = Map("a" -> 1, "b" -> 2, "c" -> 3)
m: scala.collection.immutable.Map[String,Int] = 
  Map(a -> 1, b -> 2, c -> 3)

scala> val l = List("a", "c", "b")
l: List[String] = List(a, c, b)

scala> l collect m
res0: List[Int] = List(1, 3, 2)

Hold on, how does it work? If you look at the definition of the collect method you’ll see it accepts a PartialFunction, instead I passed a Map to it. Well, it turns out that Map is a PartialFunction.

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