val listOfList = listOf(
    listOf("a", 1),
    listOf("a", 2),
    listOf("a", 3),
    listOf("b", 1),
    listOf("b", 2),
    listOf("b", 3),
    listOf("c", 1),
    listOf("c", 2),
    listOf("c", 3)
)

val filteredList = listOfList
    .groupBy { it[0] }
    .map { group ->
        listOf(
            group.key,
            group.value.maxOf { it[1] as Int }
        )
    }
println(filteredList)