How to get the list of values that belong to a group after groupBy operation in Kotlin? I have the following data: import kotlin.test.* import java.util.* data class Sales(val year: Int, val price: Int) val myList = listOf( Sales(2017, 10), Sales(2017, 19), Sales(2020, 15), Sales(2021, 100), Sales(2020, 20), ) I want to see how to get the list of values for each group. For example, I want the result as {2017=[10, 19], 2020=[15, 20], 2021=[100]}