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斯卡拉：什么是一个元素追加到一个数组的最佳方式？

分类: 技术问答 • 2022-04-04 22:44:19

斯卡拉：什么是一个元素追加到一个数组的最佳方式？

问题描述：

说我有一个数组[INT] 像

val array = Array( 1, 2, 3 )

现在我想将一个元素追加到数组，说值 4 ，如下面的例子：

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

我当然可以使用的System.arraycopy（）键，这样做我自己，但必须有这样的Scala库函数，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：


  1. 我知道我可以追加要素的另一个数组，就像下面的行，但似乎过于迂回的：

  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


  • 我知道的优点和列表VS阵列的缺点，在这里我以各种理由在延伸的阵列特别感兴趣。

  • 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.

    感谢指向的答案：+ 运算符方法。这就是我一直在寻找。不幸的是，它是而不是使用 arraycopy 定制append（）方法执行慢 - 大约2至3倍慢。综观 SeqLike [] 的实施，将创建一个生成器，然后将阵列添加到它，然后追加通过建造完成，那么生成器渲染。不是一个很好的实施阵列。我做了一个快速基准比较两种方法，寻找最快的时间十个周期。做一个单项10万元重复附加到某些类富的8元数组实例需要3.1秒， + 和1.7秒，一个简单的追加（）使用方法 System.arraycopy（）; 做千万单项追加长的8单元阵列重复需要2.1秒， + 和0.78秒，简单的追加（）方法。不知道这不可能固定在一个自定义实现库阵列？

    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?

    有关它的价值，我提起了票：
    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

    • 答

    您可以使用 + 来追加元素阵列和 + 来prePEND是：

    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)

    这是相同与任何其他的Scala集合。

    It's the same as with any other Scala collection.

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