Scala reduceByKey function - use any type that has + method

Question

I am writing a simple function called reduceByKey that takes a collection of (key, numeric) pairs and returns reduced collection by key.

  def redu         


        

Answer 1

If you are only interested in numeric values, you can use the standard Numeric type class and do this:

def reduceByKey[K,V](collection: Traversable[Tuple2[K, V]])(implicit num: Numeric[V]) = {    
  import num._
  collection
    .groupBy(_._1)
    .map { case (group: K, traversable) => traversable.reduce{(a,b) => (a._1, a._2 + b._2)} }
}

The num implicit parameter serves as an evidence that V is a numeric type, and provides the + operation for this type.