How to move an item in a Scala Seq?

Question

Let's say I have a case class like this:

case class Card(id: UUID, title: String)

and a Bucket class like this:

case class Bucket(id: UUID, title: String, cards: Seq[Card]) {
 def moveCard(cardId: UUID, newIndex: Int): Bucket = 
   copy(cards = {
    ???
  })
}

How would I fill in the moveCard() method to find the given card and move it to the new index in the sequence?

Answer 1

You can use a double dose of patch() to move an item to a new location. Unfortunately it's a little different depending on the direction, forward or back.

case class Bucket(id: UUID, title: String, cards: Seq[Card]) {
  def moveCard(cardId: UUID, newIndex: Int): Bucket = {
    val from = cards.indexWhere(_.id == cardId)
    if (from < 0) throw new Error("no such card")
    copy(cards =
      if (from < newIndex)
        cards.patch(newIndex+1,Seq(cards(from)),0).patch(from,Seq(),1)
      else
        cards.patch(newIndex,Seq(cards(from)),0).patch(from+1,Seq(),1)
        )
  }
}

---

Or this very nice simplification offered by @LeoC:

copy(cards = cards.patch(from, Seq(), 1).patch(newIndex, Seq(cards(from)), 0))