Scala-根据键从地图读取值

Question

is there any better way to read values from a map based on keys if I have more keys in a map?

currently I have a Map[String, List[String]] which can have more than 20 keys :

I am using below for retrieving values for each keys

val names= map.getOrElse("Name", List.empty)
.
.
.
val cities = map.getOrElse("City", List.Empty)

Please help If I can write this in better way.

Answer 1

I very much doubt you're doing yourself any favors by replicating the Map data into local variables.

One thing you could do is employ pattern matching to save some (not much) typing.

val knownKeys = List("Name", "City", "Country") // etc. etc.

val List(names
        ,cities
        ,countries
        // etc. etc.
        ) = knownKeys.map(data.getOrElse(_, List()))

A major drawback to this idea is that the list of keys has to be in the exact same order as the order of variables in the extraction.

A better idea is to give your Map its own default.

val data = Map("City" -> List("NY","Rome")
              ,"Name" -> List("Ed","Al")
              // etc. etc.
              ).withDefaultValue(List.empty[String])

Then you don't need .getOrElse() .

data("City")     // res0: List[String] = List(NY, Rome)
data("Airport")  // res1: List[String] = List()