kotlin list 횡렬을 종렬로 변경

data class A(val f: Int, val s: Int)

fun <T> List<T>.prepend(element: T):List<T>{
    val temp = this.toMutableList()
    temp.add(0,element)
    return temp.toList()
}

val az = listOf(A(1, 1), A(2, 1), A(3, 1))
val b = mutableListOf(
    az.map { it.f.toString() }.prepend("첫번째"),
    az.map { it.s.toString() }.prepend("두번째")
)

b.forEach {
    it.forEach {
        print(it)
    }
    println()
}