从Map中获取值，并在Scala中获得键的给定列表 [英] Getting values from Map given list of keys in Scala

问题描述

基本上，我需要从映射中获取给定列表中的键的一组值(按相同的顺序给出键).

Basically I need to get a set of values from a map for a keys in a given list (in the same order keys are given).

val kv = Map("k3" -> "v3", "k1" -> "v1", "k2" -> "v2")
val ks = List("k1", "k2")

我最好能即兴创作的是 foldRight ，胜过 ks :

The best I could have improvised is foldRight over ks:

scala> (ks foldRight List[String]()) { (v, a) => kv(v) :: a }
res7: List[String] = List(v1, v2)

在标准库中还是只有更短的代码，有没有更方便的方法来实现此目的，理想情况下是类似于 kv getVals ks 的东西吗?:)

Are there any more convenient ways to do this in standard lib or just the shorter code, ideally something alike kv getVals ks? :)

问题当然不是那么重要，只是试图探索良好的风格.

Question is not so important of course, just trying to explore towards good style.

推荐答案

使用flatMap:

 ks flatMap { k => kv get k }

或更佳:

 ks flatMap (kv get)

并且具有 for 的理解力:

for (k <- ks; v <- kv get k) yield v

但是没有一个像您自己的单行代码那样简洁明了::-)

But none are as succinct or as clear as your own one-liner: :-)

ks map kv
List("k42") map kv // will barf

但是，请注意，这是例外情况-如果 ks 包含未在地图 kv 中定义的键，则可能会引发异常.

However, note that this is exceptional - it may throw an exception if ks contains a key not defined in the map kv.

这篇关于从Map中获取值，并在Scala中获得键的给定列表的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！