将两张地图合二为一

Question

I have to maps. One is Map<String, Double> , like "USA, 55.87". Second is Map<String, String> , like "USA, United States of America".

And I want to turn this maps into Map<Result, Double> . Where Result contains two String, like "USA, United States of America". How to do that?

Answer 1

data class Result(
  val abbreviation: String,
  val name: String
)

fun main() {
  val firstMap = mapOf("USA" to 12.34, "CAN" to 56.78, "MEX" to 90.12)
  val secondMap = mapOf("USA" to "United States of America", "MEX" to "Mexico", "GON" to "Gondor")

  val result = firstMap.keys.intersect(secondMap.keys).associate { Result(it, secondMap[it]!!) to firstMap[it] }

  println(result)
}

firstMap.keys.intersect(secondMap.keys) will give you the set of keys in common between your two maps, in case there are keys that are only in one map and not the other. associate() builds a Map , where you are passed a collection member (in this case, a map key) and you return a Pair representing an entry in the resulting Map .

Answer 2

If you have strong reason to believe that the keys in both maps will always match, you can do the following:

data class Country(
    val abbreviation: String,
    val name: String
)

fun main() {
    val firstMap = mapOf("USA" to 12.34)
    val secondMap = mapOf("USA" to "United States of America")

    print(firstMap.mapKeys { Country(it.key, secondMap[it.key] ?: error("Country ${it.key} not found in second map")) })
}