在 Scala 中，有没有办法将两个列表转换为 Map？
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In Scala, is there a way to take convert two lists into a Map?
提问by Andy Hull
I have a two lists, a List[A]and a List[B]. What I want is a Map[A,B]but I want the semantics of zip. So started out like so:
我有两个列表，一个List[A]和一个List[B]。我想要的是 aMap[A,B]但我想要zip. 所以开始是这样的：
var tuplesOfAB = listOfA zip listOfB
Now I'm not sure how to construct a Mapfrom my tuplesOfAB.
现在我不确定如何Map从我的tuplesOfAB.
As a follow-up question, I also want to invert my map so that from a Map[A,B]I can create a Map[B,A]. Can anyone hit me with a clue-stick?
作为后续问题，我还想反转我的地图，以便从Map[A,B]我可以创建一个Map[B,A]. 有人可以用线索棒打我吗？
回答by oxbow_lakes
In 2.8this is really simple using the CanBuildFromfunctionality (as described by Daniel) and using breakOutwith a type instructionto the compiler as to what the result type should be:
在2.8 中，使用CanBuildFrom功能（如 Daniel 所述）和使用breakOut类型指令给编译器关于结果类型应该是什么非常简单：
import scala.collection.breakOut
val m = (listA zip listB)(breakOut): Map[A,B]
The following would also work:
以下也将起作用：
val n: Map[A,B] = (listA zip listB)(breakOut)
And (as EastSun, below, has pointed out) this has been added to the library as toMap
并且（正如下面的 EastSun 指出的那样）这已被添加到库中 toMap
val o = (listA zip listB).toMap
As for reversing the map, you can do:
至于反转地图，你可以这样做：
val r = m.map(_.swap)(breakOut): Map[B, A]
回答by Geoff Reedy
Now that you've got a list of tuples it is easy to make it into a map by writing Map(tuplesOfAB: _*). The : _*notation means to call the varargs overload with the arguments taken from the sequence. This seems like a funny bit of syntax, but it helps to think that varargs are declared like Map[A,B](pairs: (A,B)*)and the : _*is a type annotation to convert to varargs because of the common *part.
现在您已经有了一个元组列表，很容易通过编写Map(tuplesOfAB: _*). 该: _*表示法意味着使用从序列中获取的参数调用 varargs 重载。这似乎是一个有趣的语法，但它有助于认为 varargs 被声明为 likeMap[A,B](pairs: (A,B)*)并且: _*由于公共*部分，the is a type annotation to convert to varargs 。
To reverse a map muse Map(m.map(_.swap): _*). In scala a map is also a collection of pairs. This transforms those pairs by swapping the elements and passing them to the Map constructor.
要反转地图，请m使用Map(m.map(_.swap): _*). 在 Scala 中，地图也是对的集合。这通过交换元素并将它们传递给 Map 构造函数来转换这些对。
回答by Daniel C. Sobral
There's yet another way to do it, beyond those already shown. Here:
除了已经展示的方法之外，还有另一种方法可以做到这一点。这里：
Map() ++ tuplesOfAB
回答by Ashwin
scala> List( "a", "f", "d") zip List(7, 5, 4, 8) toMap
res0: scala.collection.immutable.Map[java.lang.String,Int] = Map(a -> 7, f -> 5, d -> 4)
