Scala transform list of tuples to a tuple of lists

Question

How can I transform a list of tuples List[(A,B)] to a tuple of lists (List[A], List[B])?

I have tried for following but it looks crude and I was hoping there was a better way of doing this

  val flat: List[AnyRef] = aAndB.map{ x =>
    x.map(y => List(y._1, y._2))
  }.flatMap(x => x)

  val typeA: List[A] = flat.filter {
    case x: A => true
    case _ => false
  }.map(_.asInstanceOf[A])     

  val typeB: List[B] = flat.filter {
    case x: B => true
    case _ => false
  }.map(_.asInstanceOf[B])

Michael Zajac · Accepted Answer · 2014-12-15 15:28:30Z

66

You want unzip

scala> List((1,"a"), (3, "b"), (4, "d")).unzip
res1: (List[Int], List[String]) = (List(1, 3, 4),List(a, b, d))

Similarly there is an unzip3 for List[Tuple3[A, B, C]], though anything of higher arity you'd have to implement yourself.

scala> List((1,"a", true), (3, "b", false), (4, "d", true)).unzip3
res2: (List[Int], List[String], List[Boolean]) = (List(1, 3, 4),List(a, b, d),List(true, false, true))

answered Dec 15, 2014 at 15:28

Michael Zajac

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1 Comment

Mark Lister Over a year ago

For higher arities you could use product-collections

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