在Scala中，如何合并以下地图? [英] In Scala, how can I merge maps as below?

问题描述

我想知道如何在Scala中合并地图.

I would like to know how I can merge maps in Scala.

val prevMap = Map(1-> Set("a"), 2-> Set("b"))
val newMap = Map(2-> Set("a","b"),1-> Set("c"))
val expected = Map(1->Set("a","c"), 2-> Set("a","b"))

基本上，期望的地图是newMap +添加所有在prev和new之间具有不同键的值

Basically, expected map is newMap + add all values that had a different key between prev and new

谢谢

推荐答案

像这样使用标准库

m1 ++ m2.map { case (k,v) => k -> (v ++ m1.getOrElse(k,Set())) }

请考虑第一次出现++，用于追加地图.通过将m1中的集合与一个公共键合并，可以增强++的右操作数的键值对，然后对于m1和m2中出现的任何键，运算符++替换键值对m1中的键值对在m2中；保留m1中没有出现键的m1中的键值对.

Consider the first occurrence of ++, for appending maps. The key value pairs of the right operand of ++ are enhanced by merging sets from m1 with a common key, then for any key occurring in m1 and m2, the operator ++ replaces the key value pair in m1 with the key value pair in m2; key value pairs in m1 where the key does not occur in m2 are preserved.

第二次出现的++表示设置的联合方法.因此，仅在m2中出现的那些键集保持不变(带有空集的集并集).

The second occurrence of ++ denotes the set union method. Thus, sets of those keys that occur only in m2 remain intact (set union with empty set).

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