当某些元素不是数组时,在Scala 2.8中展平数组

Question

如果我有

var a = Array(Array(1, 2), 3, Array(4,5,6))

我想把它转换成

Array(1, 2, 3, 4, 5, 6)

最简单的方法是什么？这篇文章中给出了列表的解决方案, 但它不适用于数组.

我也试过了

def flatArray(a:Array[Any])= a.map(x => x match { case ar:Array[_] => ar; case _ => Array(x) } )

但输出是类型ArraySeq,我无法看到如何将其转换为Array

Answer 1

def flatArray[T : ClassManifest](a:Array[Any]) = 
  a.flatMap{
    case ar:Array[T] => ar
    case x: T => Array(x) 
  }

我也试过使用#flatten方法,但它在NPE上失败了.

更新:回答Jus12的问题:

def flatArray[T : Manifest](a:Array[Any]) = 
  a.flatMap{
    case ar: Array[_] if ar.getClass.getComponentType == manifest[T].erasure => ar.asInstanceOf[Array[T]];
    case x => Array(x.asInstanceOf[T])
  }

当然整个解决方案并不是类型安全的.原因是适应编译器的类型推断,推断 Array(Array(1, 2), 3, Array(4,5,6))为Array[Any].准确的类型是"任何一个Int或"的数组Array[Int],但这是不可能的.什么是创建一个Either元素数组,其中每个元素都是,Either[Int, Array[Int]]并使用它:

object EitherView {
  type ||[A, B] = Either[A, B]
  // convenience of definition functions
  private def l[A,B](a: A): ||[A,B] = Left(a)
  private def r[A,B](b: B): ||[A,B] = Right(b)

  // implicit defs - stuttering-or
  implicit def aToOr2[A,B](a: A): A || B = l(a)
  implicit def bToOr2[A,B](b: B): A || B = r(b)
  implicit def aToOr3[A,B,C](a: A): A || B || C =  l(l(a))
  implicit def bToOr3[A,B,C](b: B): A || B || C = l(r(b))
  implicit def aToOr4[A,B,C,D](a: A): A || B || C || D = l(l(l(a)))
  implicit def bToOr4[A,B,C,D](b: B): A || B || C || D =  l(l(r(b)))
  implicit def aToOr5[A,B,C,D,E](a: A): A || B || C || D || E = l(l(l(l(a))))
  implicit def bToOr5[A,B,C,D,E](b: B): A || B || C || D || E = l(l(l(r(b))))
  // more? ...

}

import EitherView._

type CompoundArray[T] = Array[T || Array[T]]

object CompoundArray {
  def apply[T](elems: (T || Array[T])*) = elems.toArray
}

def flatArray[T : Manifest](a:CompoundArray[T]) = {
  a.flatMap{
    case Left(x) => Array(x)
    case Right(x) => x
  }
}

看到:

scala> val a = CompoundArray[Int](Array(1, 2), 3, Array(4,5,6))
a: Array[EitherView.||[Int,Array[Int]]] = Array(Right([I@1364b53), Left(3), Right([I@18b62e0))

scala> flatArray(a)
res0: Array[Int] = Array(1, 2, 3, 4, 5, 6)

scala> flatArray(CompoundArray[String](Array("hi"), "bye"))
res4: Array[String] = Array(hi, bye)

scala> flatArray(CompoundArray[String](Array("hi"), 3))
<console>:13: error: type mismatch;
 found   : Int(3)
 required: EitherView.||[String,Array[String]]
       flatArray(CompoundArray[String](Array("hi"), 3))
                                                    ^

注意:EitherView的最初想法是@Mitch Blevins:http://cleverlytitled.blogspot.com/2009/03/disjoint-bounded-views-redux.html