val adjList = Map("Logging" -> List("Networking", "Game"))
// val adjList: Map[String, List[String]] = Map(Logging -> List(Networking, Game))
adjList.flatMap { case (v, vs) => vs.map(n => (v, n)) }.toList
// val res7: List[(String, String)] = List((Logging,Game))
adjList.map { case (v, vs) => vs.map(n => (v, n)) }.flatten.toList
// val res8: List[(String, String)] = List((Logging,Networking), (Logging,Game))
我不確定這里發生了什么。我期待他們倆的結果相同。
uj5u.com熱心網友回復：
.flatMap是Map的.flatMap，但是.map是Iterable的.map。
對于 aMap "Logging" -> "Networking"并"Logging" -> "Game"成為后者"Logging" -> "Game"，因為鍵是相同的。
val adjList: Map[String, List[String]] = Map("Logging" -> List("Networking", "Game"))
val x0: Map[String, String] = adjList.flatMap { case (v, vs) => vs.map(n => (v, n)) }
//Map(Logging -> Game)
val x: List[(String, String)] = x0.toList
//List((Logging,Game))
val adjList: Map[String, List[String]] = Map("Logging" -> List("Networking", "Game"))
val y0: immutable.Iterable[List[(String, String)]] = adjList.map { case (v, vs) => vs.map(n => (v, n)) }
//List(List((Logging,Networking), (Logging,Game)))
val y1: immutable.Iterable[(String, String)] = y0.flatten
//List((Logging,Networking), (Logging,Game))
val y: List[(String, String)] = y1.toList
//List((Logging,Networking), (Logging,Game))
還有https://users.scala-lang.org/t/map-flatten-flatmap/4180
轉載請註明出處，本文鏈接：https://www.uj5u.com/net/512167.html
標籤：斯卡拉平面图