MappedOrdering

MappedOrdering.scala

/**
 * Defines an ordering for a list of keys of type K given an implicit ordering
 * on value V and a mapping from K to V
 */
object MappedOrdering {
  def withMapping[K, V](mapping: K => V)(implicit ordering: Ordering[V]) = {
    new MappedOrdering[K, V](mapping)(ordering)
  }
}

class MappedOrdering[K, V](mapping: K => V)(implicit ordering: Ordering[V]) extends Ordering[K] {
  override def compare(first: K, second: K) = {
    ordering.compare(mapping(first), mapping(second))
  }
}