Looking for a solution to a coding question

Good folk of Scala Users,
I have a puzzle, that I’m embarrassed to admit, is causing me some trouble to solve. I wonder whether anyone here would like to suggest a way to solve this? Here is the code…
` /*
* This is a sample solution to the Wish Solitaire game, as described below, and at:
* Wish Solitaire | Bicycle Playing Cards
* The Pack
* Remove all 2s through 6s, to form a deck of 32 cards
* The Deal
* Shuffle cards and deal 4 cards face down into a pile on the table. Deal the whole
* deck into piles of 4 cards, lining the piles up so that there are 8 total piles
* in a row from left to right.
* The Play
* Turn over the top cards of each pile so that they are face up. Take any cards
* that are pairs of the same kind, regardless of suit - two 10’s, two Kings, etc.
* and clear them away.
* Once you have removed a card from the top of the pile, turn over the next card
* on the pile so it is face up.
* To win the game, you must clear away all piles in pairs.
package example

import scala.util.Random

case class Card(suit: String, rank: String) {}

object WishSolitaire {
  val suits = List[String]("Hearts", "Clubs", "Diamonds", "Spades")
  val ranks = List[String]("Ace", "7", "8", "9", "10", "Jack", "Queen", "King")
  val aDeck = for {
    s <- suits
    r <- ranks
  } yield Card(s, r)

  def main(args: Array[String]) : Unit = {
    val piles = Random.shuffle(aDeck).grouped(4).toList

    val r = piles map { x => x map { _.rank  } }  // just to see result of shuffle....

/*  Recursive function to match pairs, remove the 'head' from the list containing matching ranks
 *  until game is finished, or no more progress can be made.
    def play(deck: List[List[Card]], remainingHands: Int, nomatch: Boolean ) = {
      if (0 < remainingHands && nomatch) println("Game has no solution")
      else if (0 == remainingHands) println("Game Over!!")
      else {
        // compare ranks of all 8 hands for 2 equal ranks
        // for all pairs of 2 matched rank, remove the head
        // repeat
        // if a 'hand' (list.length == 0) has been emptied, decrement remainingHands
        // if no matches set cannot complete to true??
        val cannotBeCompleted = true
        play(deck, remainingHands, cannotBeCompleted)
    // play(piles, piles.length, false)


What is the nature of the trouble you’re having? Where are you stuck?

Hello Seth,
Principally, how to traverse a list of list[Card], and find pairs of equal values (card.rank)?
Once found, I can ‘remove’ the (equal) items from the the ‘inner’ lists. Then recurse over the list of lists until a terminating condition is satisfied. I hope that makes some sense?
I realise it can be done in an imperative manner, but I am really looking for a functional / (idiomatic) scala way.