Collections: Associating the data using some key

Observation

• The advantage here is observe we were able to convert the list of objects into a map by using one of the fields of the objects in the list of each item.
• Also notice I had duplicate entry as key that was removed from output

Code

data class Country(val id : Int, val name: String, val isDemocracy: Boolean)
val countriesList = mutableListOf(
    Country(id = 1, name = "USA", isDemocracy = true),
    Country(id = 2, name = "Australia", isDemocracy = true),
    Country(id = 3, name = "Russia", isDemocracy = false),
    Country(id = 4, name = "England", isDemocracy = true),
    Country(id = 5, name = "North Korea", isDemocracy = false),
    Country(id = 5, name = "South Korea", isDemocracy = false)
)


fun main(args: Array<String>) {

    val mapOfObjects = countriesList.associateBy {
        it.id
    }

    mapOfObjects.forEach{
        println(it.value.name)
    }

}

Output

USA
Australia
Russia
England
South Korea