如何在列表中找到匹配的元素并将其映射为 Scala API 方法? [英] How to find a matching element in a list and map it in as an Scala API method?

问题描述

是否有一种方法可以在不执行这两种方法的情况下执行以下操作:find 和 map?

Is there a method to do the following without doing both methods: find and map?

val l = 0 to 3
l.find(_ * 33 % 2 == 0).map(_ * 33) // returns Some(66)

推荐答案

使用 collect 怎么样?

How about using collect?

// Returns List(66)
List(1, 2, 3) collect { case i if (i * 33 % 2 == 0) => i * 33 }

然而，这将返回所有匹配项，而不仅仅是第一个.

However that will return all matches and not just the first one.

更好的答案是，基于 Scala 2.9:

The better answer would have been, based on Scala 2.9:

// Returns Some(66)
List(1, 2, 3) collectFirst { case i if (i * 33 % 2 == 0) => i * 33 }

在评论中建议附加一个 head 以获得 Scala 2.8 版本的解决方案不是很有效，恐怕.也许在那种情况下，我会坚持使用您自己的代码.无论如何，为了确保它返回一个选项，你不应该调用head，而是headOption.

The solution suggested in the comments to append a head to get a Scala 2.8 version of that is not very efficient, I'm afraid. Perhaps in that case I would stick to your own code. In any case, in order to make sure it returns an option, you should not call head, but headOption.

// Returns Some(66)
List(1, 2, 3) collect { case i if (i * 33 % 2 == 0) => i * 33 } headOption

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