斯卡拉：如何由元組

Question

設的第一個元素合併列表說我有一個列表：

[(A, a), (A, b), (A, c), (B, a), (B, d)] 

如何作出這樣的名單爲：

[(A, [a,b,c]), (B, [a,d])] 

與單一功能？

感謝

Answer 1

的groupBy功能可以實現這一點：

scala> val list = List((1, 'a'), (1, 'b'), (1, 'c'), (2, 'a'), (2, 'd')) 
list: List[(Int, Char)] = List((1,a), (1,b), (1,c), (2,a), (2,d)) 

scala> list.groupBy(_._1) // grouping by the first item in the tuple 

res0: scala.collection.immutable.Map[Int,List[(Int, Char)]] = Map(2 -> List((2,a), (2,d)), 1 -> List((1,a), (1,b), (1,c))) 

Answer 2

只是做GROUPBY不會給你你想要的預期格式。所以我建議你爲此寫一個自定義方法。

def groupTuples[A,B](seq: Seq[(A,B)]): List[(A, List[B])] = { 
    seq. 
    groupBy(_._1). 
    mapValues(_.map(_._2).toList).toList 
} 

然後調用它以獲得所需的結果。

val t = Seq((1,"I"),(1,"AM"),(1, "Koby"),(2,"UP"),(2,"UP"),(2,"AND"),(2,"AWAY")) 

groupTuples[Int, String](t)