flatten和flatMap（identity）有什么区别吗？ [英] Is there any difference between flatten and flatMap(identity)?

问题描述

scala> List(List(1), List(2), List(3), List(4))
res18: List[List[Int]] = List(List(1), List(2), List(3), List(4))

scala> res18.flatten
res19: List[Int] = List(1, 2, 3, 4)

scala> res18.flatMap(identity)
res20: List[Int] = List(1, 2, 3, 4)

这两个函数有什么区别吗？什么时候适合使用其中一种？是否有权衡？

Is there any difference between these two functions? When is it appropriate to use one over the other? Are there any tradeoffs?

推荐答案

您可以查看 flatMap（identity）作为地图（标识）.flatten 。 （当然，它不会以这种方式实现，因为它需要两次迭代）。

You can view flatMap(identity) as map(identity).flatten. (Of course it is not implemented that way, since it would take two iterations).

map（identity）为您提供相同的集合，因此最终它与 flatten 。

map(identity) gives you the same collection, so in the end it is the same as only flatten.

我个人坚持 flatten ，因为它更短/更容易理解，并设计为准确做到这一点。

I would personally stick to flatten, since it is shorter/easier to understand and designed to exactly do this.

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