I have 2 different lists: listA has objA elements, with these properties: country, language listB h...

# getting-started

[Daniele B]

I have 2 different lists:

listA has objA elements, with these properties: country, language
listB has objB elements, with these properties: country, population

I would like to merge them by creating listC, with properties: country, language, population

How can I do that?

[diesieben07]

val languages = listOf<A>()
    val populations = listOf<B>()
    val populationsByCountry = populations.associateBy { it.country }
    val result = languages.map { C(it.country, it.language, checkNotNull(populationsByCountry[it.country]).population) }

[Daniele B]

Oh, I see, very interesting. AssociateBy is creating a map out of the list. Great!
Many thanks!

[nanodeath]

another heavier way, but a little more flexible way, is to call associateBy on both lists, and then say (populationsByCountry.keySet + languagesByCountry.keySet).map { ... }. then you can error if an item is missing from either collection.