Priority Queue of HashMaps in Scala

Question

I'm trying to update the value of an element of my Priority Queue of HashMaps put with no success. Here's is how I'm doing:

def HashMapOrdering = new Ordering[HashMap[Int,Int]] {

  def compare(a : HashMap[Int,Int], b : HashMap[Int,Int]) = b.valuesIterator.next().compare(a.valuesIterator.next())

}

def main(args: Array[String]) {

  var seeds = PriorityQueue[HashMap[Int, Int]]()(HashMapOrdering)
  seeds.enqueue(HashMap(4 -> 4), HashMap(234 -> 5), HashMap(78 -> 6), HashMap(89 -> 1))

  seeds.find(x => x.get(89) == 1) match {

    case Some(hashMap: HashMap[Int, Int]) => hashMap.remove(77); hashMap.put(77,32)
    case None => println("Not found")

  }

}

Unfortunately, I always got the "Not found" message. Any ideias on what am I doing wrong or how to update the hash's values?

Answer 1

Obviously you've got a type mismatch. If you look the definition of get function, you'll see the following ( http://www.scala-lang.org/api/2.11.6/index.html#scala.collection.mutable.HashMap ):

def get(key: A): Option[B]

That means, that it returns value in your case typed as Option[Int] . So wrap your right condition argument in an Option monad:

seeds.find(x => x.get(89) == Some(1)) match {
    case Some(hashMap: HashMap[Int, Int]) => {
        hashMap.remove(77)
        hashMap.put(77,32)
    }
    case None => println("Not found")
}

Works as expected.

PS Forgot about your question about updating: you can use an update function instead of using remove and put : hashMap.update(77, 32)