从 List 中获取前 n 个元素
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时间：2020-09-11 02:10:11 来源:igfitidea点击:
Get first n elements from List
提问by john smith
I have a List
我有一个 List
val family=List("1","2","11","12","21","22","31","33","41","44","51","55")
i want to take its first n elements but the problem is that parentssize is not fixed.
我想取它的前 n 个元素，但问题是parents大小不固定。
val familliar=List("1","2","11") //n=3
回答by Ende Neu
You can use take
您可以使用 take
scala> val list = List(1,2,3,4,5,6,7,8,9)
list: List[Int] = List(1, 2, 3, 4, 5, 6, 7, 8, 9)
scala> list.take(3)
res0: List[Int] = List(1, 2, 3)
回答by Xiaohe Dong
List(1,2,3).take(100) //List(1,2,3)
The signature of take will compare the argument with index, so the incremental index will never more than argument
take 的签名会将参数与索引进行比较，因此增量索引永远不会超过参数
The signature of take
采取的签名
override def take(n: Int): List[A] = {
val b = new ListBuffer[A]
var i = 0
var these = this
while (!these.isEmpty && i < n) {
i += 1
b += these.head
these = these.tail
}
if (these.isEmpty) this
else b.toList
}
