Zip 2 HashMap（或字典）

Question

什麼是在Scala中壓縮兩個字典的功能方式？

map1 = new HashMap("A"->1,"B"->2) 
map2 = new HashMap("B"->22,"D"->4) // B is the only common key 

zipper(map1,map2)應該給類似的東西來

Seq(("A",1,0), // no A in second map, so third value is zero 
     ("B",2,22), 
     ("D",0,4)) // no D in first map, so second value is zero 

如果沒有的功能，任何其他樣式也可以理解使用get

Answer 1

def zipper(map1: Map[String, Int], map2: Map[String, Int]) = { 
    for(key <- map1.keys ++ map2.keys) 
    yield (key, map1.getOrElse(key, 0), map2.getOrElse(key, 0)) 
} 


scala> val map1 = scala.collection.immutable.HashMap("A" -> 1, "B" -> 2) 
map1: scala.collection.immutable.HashMap[String,Int] = Map(A -> 1, B -> 2) 

scala> val map2 = scala.collection.immutable.HashMap("B" -> 22, "D" -> 4) 
map2: scala.collection.immutable.HashMap[String,Int] = Map(B -> 22, D -> 4) 

scala> :load Zipper.scala 
Loading Zipper.scala... 
zipper: (map1: Map[String,Int], map2: Map[String,Int])Iterable[(String, Int, Int)] 

scala> zipper(map1, map2) 
res1: Iterable[(String, Int, Int)] = Set((A,1,0), (B,2,22), (D,0,4)) 

注可能是最好getOrElse在這種情況下。 None用於指定值不存在，而不是使用0。