Scala: List[Tuple3] to Map[String,String]

问题

I've got a query result of List[(Int,String,Double)] that I need to convert to a Map[String,String] (for display in an html select list)

My hacked solution is:

val prices = (dao.getPricing flatMap {
  case(id, label, fee) =>
    Map(id.toString -> (label+" $"+fee))
  }).toMap

there must be a better way to achieve the same...

回答1:

A little more concise:

val prices =
  dao.getPricing.map { case (id, label, fee) => ( id.toString, label+" $"+fee)} toMap

shorter alternative:

val prices =
  dao.getPricing.map { p => ( p._1.toString, p._2+" $"+p._3)} toMap

回答2:

How about this?

val prices: Map[String, String] =
  dao.getPricing.map {
    case (id, label, fee) => (id.toString -> (label + " $" + fee))
  }(collection.breakOut)

The method collection.breakOut provides a CanBuildFrom instance that ensures that even if you're mapping from a List, a Map is reconstructed, thanks to the type annotation, and avoids the creation of an intermediary collection.

来源：https://stackoverflow.com/questions/10785372/scala-listtuple3-to-mapstring-string