None if no clear winner in Scala Map maxBy

Question

val valueCountsMap: mutable.Map[String, Int] = mutable.Map[String, Int]()
valueCountsMap("a") = 1
valueCountsMap("b") = 1
valueCountsMap("c") = 1

val maxOccurredValueNCount: (String, Int) = valueCountsMap.maxBy(_._2)
// maxOccurredValueNCount: (String, Int) = (b,1)

How can I get None if there's no clear winner when I do maxBy values? I am wondering if there's any native solution already implemented within scala mutable Maps.

Answer 1

No, there's no native solution for what you've described.

Here's how I might go about it.

implicit class UniqMax[K,V:Ordering](m: Map[K,V]) {
  def uniqMaxByValue: Option[(K,V)] = {
    m.headOption.fold(None:Option[(K,V)]){ hd =>
      val ev = implicitly[Ordering[V]]
      val (count, max) = m.tail.foldLeft((1,hd)) {case ((c, x), v) =>
        if (ev.gt(v._2, x._2)) (1, v)
        else if (v._2 == x._2) (c+1, x)
        else                   (c, x)
      }
      if (count == 1) Some(max) else None
    }
  }
}

Usage:

Map("a"->11, "b"->12, "c"->11).uniqMaxByValue    //res0: Option[(String, Int)] = Some((b,12))
Map(2->"abc", 1->"abx", 0->"ab").uniqMaxByValue  //res1: Option[(Int, String)] = Some((1,abx))
Map.empty[Long,Boolean].uniqMaxByValue           //res2: Option[(Long, Boolean)] = None
Map('c'->2.2, 'w'->2.2, 'x'->2.1).uniqMaxByValue //res3: Option[(Char, Double)] = None