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]}
CodePudding user response:
You can use the following:
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),
)
fun main () {
val reduced = myList.groupBy({ it.year } , { it.price })
print(reduced) //result: {2017=[10, 19], 2020=[15, 20], 2021=[100]}
// further - just for understanding
val reduced2 = myList.groupBy({ it.year } , { it})
print(reduced2)
//result:
//{
//2017=[Sales(year=2017, price=10), Sales(year=2017, price=19)],
//2020=[Sales(year=2020, price=15), Sales(year=2020, price=20)],
//2021=[Sales(year=2021, price=100)]
//}
}
CodePudding user response:
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)
)
val result = myList
.groupBy { it.year }
.mapValues { (_, value) -> value.map { it.price } }
println(result) // Output: {2017=[10, 19], 2020=[15, 20], 2021=[100]}