定义一个二维列表并在 for 循环中将列表附加到它，scala

Question

我想在 for 循环之前定义一个 2d 列表，然后我想在 for 循环中将 1d 列表附加到它，如下所示：

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

上面的代码不起作用。但是我似乎找不到解决这个问题的办法，而且很简单！

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))

更好的是：

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

Answer 2

如果你想让2dEmptyList可变，请考虑使用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?))

定义一个二维列表并在 for 循环中将列表附加到它，scala

Define a 2d list and append lists to it in a for loop, scala

2d

scala

list

append