Main.kt

/**
 * You can edit, run, and share this code. 
 * play.kotlinlang.org 
 */
data class MyResponse(
        val bigger: Int,
        val lower: Int
)

fun main() {
   val words = listOf("a", "abc", "ab", "def", "abcd")
   val byLength = words.groupBy { when {
       it.length > 2 -> "bigger"
       else -> "lower"
   } }.let { group ->
       MyResponse(
           bigger = group?.get("bigger").let {
              it?.size ?: 0 
           },
           lower = group?.get("lower").let {
              it?.size ?: 0 
           }
       )
      
   }
   println(byLength.toString())
}

The real code is a bit different. I want to group some "record-set" and to"map" it to data object.
Link to Kotlin playground where you can test it:
https://play.kotlinlang.org/#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