如何在scala中组合过滤器和地图？ [英] How to combine filter and map in scala?

问题描述

我在 Scala 中有列表[Int] 。列表是列表（1,2,3,4,5,6,7,8,9,10）。我想要 filter 列表，使它只有偶数。我想用2号数字来代替。可以吗？

I have List[Int] in Scala. The List is List(1,2,3,4,5,6,7,8,9,10). I want to filter the list so that it only has even numbers. And I want to muliply the numbers with 2. Is it possible?

我希望我能清楚地解释这个问题。如果你有任何问题，请问。

I hope I have explained the question clearly. If u have any questions then please ask. THanks in advance.

推荐答案

正如我在我的评论中所说，收集应该做你想要的：

As I state in my comment, collect should do what you want:

list.collect{
  case x if x % 2 == 0 => x*2
}

收集方法允许您同时指定匹配元素（ filter ）的条件，并修改匹配的值（ map ）

The collect method allows you to both specify a criteria on the matching elements (filter) and modify the values that match (map)

而且，在@TravisBrown建议的情况下，您也可以使用 flatMap ，特别是在条件为更复杂，不适合作为防卫条件。这样的例子如下：

And as @TravisBrown suggested, you can use flatMap as well, especially in situations where the condition is more complex and not suitable as a guard condition. Something like this for your example:

list.flatMap{
  case x if x % 2 == 0 => Some(x*2)
  case x => None
}

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