Is there a safe way in Scala to transpose a List of unequal-length Lists?

Question

Given the following List:

val l = List(List(1, 2, 3), List(4, 5), List(6, 7, 8))

If I try to transpose it, Scala will throw the following e

Answer 1

This is probably the cleanest:

def transpose[T](l: List[List[T]]): List[List[T]] =
     l.flatMap(_.headOption) match {
         case Nil => Nil
         case head => head :: transpose(l.map(_.drop(1)))
     }

or a modified version that is even more efficient:

def transpose[T](l: List[List[T]]): List[List[T]] =
     l.flatMap(_.headOption) match {
         case Nil => Nil
         case head => head :: transpose(l.collect { case _ :: tail => tail })
     }