Scala:将元素附加到数组的最佳方法是什么? [英] Scala: what is the best way to append an element to an Array?

问题描述

假设我有一个 Array[Int] 之类的

Say I have an Array[Int] like

val array = Array( 1, 2, 3 )

现在我想在数组中附加一个元素，比如值 4，如下例所示:

Now I would like to append an element to the array, say the value 4, as in the following example:

val array2 = array + 4     // will not compile

我当然可以使用 System.arraycopy() 并自行完成此操作，但必须有一个 Scala 库函数用于此目的，而我根本找不到.感谢您的指点！

I can of course use System.arraycopy() and do this on my own, but there must be a Scala library function for this, which I simply could not find. Thanks for any pointers!

注意事项:

1. 我知道我可以附加另一个元素数组，如下行所示，但这似乎太迂回了:

1. I am aware that I can append another Array of elements, like in the following line, but that seems too round-about:

val array2b = array ++ Array( 4 )     // this works

我了解 List 与 Array 的优缺点，出于各种原因，我特别对扩展 Array 感兴趣.

I am aware of the advantages and drawbacks of List vs Array and here I am for various reasons specifically interested in extending an Array.

编辑 1

感谢指向 :+ 运算符方法的答案.这就是我一直在寻找的.不幸的是，它比使用 arraycopy 的自定义 append() 方法实现要慢——大约慢两到三倍.查看 SeqLike[] 中的实现，创建了一个构建器，然后将数组添加到其中，然后通过构建器完成追加，然后呈现构建器.不是一个好的数组实现.我做了一个比较两种方法的快速基准测试，查看十个周期中最快的时间.将单个项目附加到某个类 Foo 的 8 元素数组实例的 1000 万次重复使用 :+ 需要 3.1 秒，使用简单的 需要 1.7 秒append() 方法使用 System.arraycopy(); 在 Long 的 8 元素数组上执行 1000 万次单项追加重复需要 2.1 秒，:+ 和 0.78 秒，使用简单的 append() 方法.想知道这是否无法通过 Array 的自定义实现在库中修复?

Edit 1

Thanks for the answers pointing to the :+ operator method. This is what I was looking for. Unfortunately, it is rather slower than a custom append() method implementation using arraycopy -- about two to three times slower. Looking at the implementation in SeqLike[], a builder is created, then the array is added to it, then the append is done via the builder, then the builder is rendered. Not a good implementation for arrays. I did a quick benchmark comparing the two methods, looking at the fastest time out of ten cycles. Doing 10 million repetitions of a single-item append to an 8-element array instance of some class Foo takes 3.1 sec with :+ and 1.7 sec with a simple append() method that uses System.arraycopy(); doing 10 million single-item append repetitions on 8-element arrays of Long takes 2.1 sec with :+ and 0.78 sec with the simple append() method. Wonder if this couldn't be fixed in the library with a custom implementation for Array?

为了它的价值，我提交了一张票:https://issues.scala-lang.org/browse/SI-5017

For what it's worth, I filed a ticket: https://issues.scala-lang.org/browse/SI-5017

推荐答案

您可以使用 :+ 将元素附加到数组，并使用 +: 附加它:

You can use :+ to append element to array and +: to prepend it:

0 +: array :+ 4

应该产生:

res3: Array[Int] = Array(0, 1, 2, 3, 4)

它与 Seq 的任何其他实现相同.

It's the same as with any other implementation of Seq.

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