合并地图科特林中的值 [英] Merge values in map kotlin

问题描述

我需要将带有名称"-电话号码"对的映射mapA和mapB合并到最终映射中，将重复键的值粘贴在一起，并用逗号分隔.重复值只能添加一次. 就语言方式而言，我需要最惯用和正确的方法.

I need merge maps mapA andmapB with pairs of "name" - "phone number" into the final map, sticking together the values for duplicate keys, separated by commas. Duplicate values should be added only once. I need the most idiomatic and correct in terms of language approach.

例如:

val mapA = mapOf("Emergency" to "112", "Fire department" to "101", "Police" to "102")
val mapB = mapOf("Emergency" to "911", "Police" to "102")

最终结果应如下所示:

{"Emergency" to "112, 911", "Fire department" to "101", "Police" to "102"}

这是我的功能:

fun mergePhoneBooks(mapA: Map<String, String>, mapB: Map<String, String>): Map<String, String> {
    val unionList: MutableMap <String, String> = mapA.toMutableMap()
    unionList.forEach { (key, value) -> TODO() } // here's I can't come on with a beatiful solution

    return unionList
}

推荐答案

怎么样:

val unionList = (mapA.asSequence() + mapB.asSequence())
    .distinct()
    .groupBy({ it.key }, { it.value })
    .mapValues { (_, values) -> values.joinToString(",") }

结果:

{Emergency=112,911, Fire department=101, Police=102}

这将:

• 同时生成两个地图的键值对的Sequence
• 按键对它们进行分组(结果:Map<String, List<String>)
• 将它们的值映射到逗号连接的字符串(结果:Map<String, String>)

• produce a lazy Sequence of both maps' key-value pairs
• group them by key (result: Map<String, List<String>)
• map their values to comma-joined strings (result: Map<String, String>)

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