定義二維表並追加名單，它在一個for循環，斯卡拉

Question

我想定義一個二維列表前一個for循環事後我想追加到它1D列出一個for循環，像這樣：

var 2dEmptyList: listOf<List<String>> 
for (element<-elements){ 
    ///do some stuff 
    2dEmptyList.plusAssign(1dlist) 
} 

上面的代碼不起作用。但我似乎無法找到解決方案，它非常簡單！

Answer 1

scala> val elements = List("a", "b", "c") 
elements: List[String] = List(a, b, c) 

scala> val twoDimenstionalList: List[List[String]] = List.empty[List[String]] 
twoDimenstionalList: List[List[String]] = List() 

scala> val res = for(element <- elements) yield twoDimenstionalList ::: List(element) 
res: List[List[java.io.Serializable]] = List(List(a), List(b), List(c)) 

更妙的是：

scala> twoDimenstionalList ::: elements.map(List(_)) 
res8: List[List[String]] = List(List(a), List(b), List(c)) 

Answer 2

如果你想2dEmptyList是可變的，請考慮使用scala.collection.mutable.ListBuffer：

scala> val ll = scala.collection.mutable.ListBuffer.empty[List[String]] 
ll: scala.collection.mutable.ListBuffer[List[String]] = ListBuffer() 

scala> ll += List("Hello") 
res7: ll.type = ListBuffer(List(Hello)) 

scala> ll += List("How", "are", "you?") 
res8: ll.type = ListBuffer(List(Hello), List(How, are, you?))