如何从 Scala 的数组中选择一个随机元素？
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How to choose a random element from an array in Scala?
提问by sam
For example, there is a Scala array val A = Array("please", "help", "me"). How to choose a random element from this array?
例如，有一个 Scala 数组val A = Array("please", "help", "me")。如何从这个数组中选择一个随机元素？
采纳答案by topless
import java.util.Random
// ...
val rand = new Random(System.currentTimeMillis())
val random_index = rand.nextInt(A.length)
val result = A(random_index)
回答by user1338062
import scala.util.Random
val A = Array("please", "help", "me")
Random.shuffle(A.toList).head
回答by ahogue
import scala.util.Random
val A = List(1, 2, 3, 4, 5, 6)
A(Random.nextInt(A.size))
回答by Raphael Bobillot
We can also add some safety with the Optionmonad (using the liftfunction, and a condition)
我们还可以为Optionmonad添加一些安全性（使用lift函数和条件）
Actually, if you use this function on Arrays (that could be empty), your result will always be an Option.
实际上，如果您在数组（可能为空）上使用此函数，您的结果将始终是一个选项。
Referencial Transparency FTW \o/
参考透明度 FTW \o/
def getRandElemO[T](arr: Array[T]): Option[T] =
if (arr.isEmpty) None
else arr lift util.Random.nextInt(arr.length)
回答by Rodrigo Hernández Mota
If you want a more idiomatic solution, consider using the typeclass pattern (implicit classes in scala).
如果您想要更惯用的解决方案，请考虑使用 typeclass 模式（scala 中的隐式类）。
implicit class ListOps[A](list: List[A]) {
def getRandomElement: Option[A] = list match {
case Nil => None
case _ => list.lift(scala.util.Random.nextInt(list.size))
}
def randomChoice(n: Int): Option[List[A]] =
(1 to n).toList.foldLeft(Option(List[A]()))((acc, e) => getRandomElement.flatMap(r => acc.map(a => a :+ r)))
}
Now if the implicit class is in scope, you can:
现在，如果隐式类在范围内，您可以：
val randomElement: Option[String] = List("this", "is", "a", "list").getRandomElement
If you are sure that the option contains some value, you can use the getmethod.
如果您确定该选项包含某个值，则可以使用该get方法。
randomElement.get // This will return a String (or a NotSuchElementExeption)
Nonetheless, pattern matching or getOrElseare recommended:
尽管如此，还是getOrElse建议使用模式匹配：
randomElement match {
case None => ??? // This is what you do when a None is encounter (e.g. for empty lists)
case Some(result) => ??? // The variable result contains a string.
Notethat the randomChoicemethod assumes substitution of elements.
请注意，该randomChoice方法假定元素替换。
回答by Josh Weinstein
A better answer that does not involve reshuffling the array at all would be this:
一个完全不涉及重新洗牌的更好的答案是：
import scala.util.Random
object sample {
//gets random element from array
def arr[T](items:Array[T]):T = {
items(Random.nextInt(items.length))
}
}
This also works generically
这也适用于一般情况
