Scala List 操作 list中最大数的下标 Vector转List

1.List操作

take takeRight takeWhile

val nums = List(1,1,1,1,4,4,4,4)
val left = nums.take(4)       //List(1,1,1,1)
val right = nums.takeRight(4)  //List(4,4,4,4)
val headNums = nums.takeWhile(_==nums.head)   //List(1,1,1,1)

drop dropRight dropWhile

val nums = List(1,2,3,4,5,6,7,8)
val left = nums.drop(3) //List(4,5,6,7,8)
val right = nums.dropRight(3)  //List(1,2,3,4,5)
val tailNums = nums.dropWhile(_==nums.head) //List(2,3,4,5,6,7,8)

indexOf indexWhere

indexOf(‘?’) for a list not working

scala> val lst = List("question?mark")
lst: List[String] = List(question?mark)

scala> lst.indexOf('?')
res2: Int = -1
//列表lst中只有一个元素"question?mark",不等于"?"，所以indexOf('?')没找到匹配项，返回-1

//可以用
scala> lst.indexWhere(_.contains("?"))
res3:Int = 0
scala> lst(0).indexOf('?')
res4: Int = 8
scala> "where is ?".indexOf('?')
res5: Int = 9

scala> val lst = List("question?mark","where?","hello","why?")
lst: List[String] = List(question?mark, where?, hello, why?)

scala> lst.map(_.indexOf('?'))
res6: List[Int] = List(8, 5, -1, 3)

2.找出list中最大的数的下标

scala> List(0, 43, 1, 34, 10).zipWithIndex.maxBy(_._1)._2
res0: Int = 1

3.Vector转List

Create list from vector in scala

定义一个方法：输入一个Vector，输出一个List，List的元素和Vector的元素相同。

List在Scala中是不可变的（immutable）,改变一个List（的长度之类）事实上是yield一个List的新实例。

List的map方法不改变the container,只改变包含的values。

val v = Vector(1,2,3)
v:scala.collection.immutable.Vector[Int] = Vector(1,2,3)
v.toList
res0:List[Int] = List(1,2,3)

//或者：
List(Vector(1,2,3):_*)