将Seq [（A，Future [B]）]转换为Scala中的Future [Map [A​​，B]]

Question

我正在寻找一种将Seq[(A, Future[B])]转换为Future[Map[A,B]]的简洁方法。有没有办法做到这一点？提前谢谢！

Answer 1

如果你被允许scalaz，那么是：

val original:Seq[(String,Future[Int])] = Seq("a" -> Future.successful(1))
val transformed:Future[Map[String,Int]] = original.toMap.sequenceU

Answer 2

您可以使用map和flatMap转换Futures。使用它，您可以从Future计算空地图开始，使用flatMap和map来聚合其他期货：

val s = Seq("A" -> Future {1}, "B" -> Future {2})
val m = s.foldLeft(Future.successful(Map[String,Int]())){
  case (result, (key, future)) => result.flatMap{
    map => future.map{
      value => map + (key -> value)
    }
  }
}

Answer 3

或

val s = Seq( ("1", f1), ("2", f2) )
Future.sequence( s.map { case (k ,v) => v.map(fv => (k ,fv)) } ).map(_.toMap)

Answer 4

这并不难。您需要三个步骤：

 //1. create a list of future tuples
 val futureTuples = Future.map { case (a, futureB) => futureB.map ( a -> _ }
 //2. Transorm it to a future list
 val futureList = Future.sequence(futureTuples)
 //3. Finally, convert list to map:
 val futureMap = futureList.map { _.toMap }