list.scala

list_unzip_or_foldleft.scala

scala> val aa: List[(List[Int], List[Int])] =
     |   List((List(1, 2, 3), List(4, 5, 6)), (List(7, 8, 9), List(10, 11, 12)))
     | val bb: (List[Int], List[Int]) = (List(1, 2, 3, 7, 8, 9), List(4, 5, 6, 10, 11, 12))
val aa: List[(List[Int], List[Int])] = List((List(1, 2, 3),List(4, 5, 6)), (List(7, 8, 9),List(10, 11, 12)))
val bb: (List[Int], List[Int]) = (List(1, 2, 3, 7, 8, 9),List(4, 5, 6, 10, 11, 12))

scala> aa.unzip.map[[t] =>> List[Int]](
     |     [t] => (_: t) match {
     |     case x: List[List[Int]] => x.flatten
     |   }
     | )
                    ^
       error: identifier expected but '[' found.

scala> aa.unzip match { case (a, b) => (a.flatten, b.flatten) }
val res7: (List[Int], List[Int]) = (List(1, 2, 3, 7, 8, 9),List(4, 5, 6, 10, 11, 12))

scala> aa.foldLeft((List.empty[Int], List.empty[Int])) { case ((a, b), (c, d)) => (a ++ c, b ++ d) }
val res10: (List[Int], List[Int]) = (List(1, 2, 3, 7, 8, 9),List(4, 5, 6, 10, 11, 12))

// scala 3에서 가능하다고 함. Tuple#map과 polymorphic function 사용: https://scastie.scala-lang.org/cbEqHtQhRUSev5Ng4eJoUA

OptionSeq_map_getOrElse_filter.scala

scala> case class Names(firstName: String, lastName: String)
class Names

scala> val m: Option[Seq[Names]] = Some(List(Names("f1", "l1"), Names("f2", "l2")))
val m: Option[Seq[Names]] = Some(List(Names(f1,l1), Names(f2,l2)))

scala> val n: Option[Seq[Names]] = None
val n: Option[Seq[Names]] = None

scala> def getLastName(names: Option[Seq[Names]]) = names.map(x => x.map(t => s"${t.firstName} ${t.lastName}")).getOrElse(List.empty).filter(_.trim != "")
def getLastName(names: Option[Seq[Names]]): Seq[String]

scala> getLastName(m)
val res5: Seq[String] = List(f1 l1, f2 l2)

scala> getLastName(n)
val res6: Seq[String] = List()