def mapper_predict_songs(song: Int, similar_songs: Iterable[(Int,Int,Double)]) : Iterable[(Int,Double)] = {
      val result = new ListBuffer[(Int,Double)]

      val sim_songs = new scala.collection.mutable.HashMap[Int,Double]()
      val playlists = new scala.collection.mutable.HashMap[Int,scala.collection.mutable.Set[Int]]

      for(tuple <- similar_songs){
        val s = tuple._1
        val u = tuple._2
        val n = tuple._3
        if(!playlists.contains(u))
          playlists(u) = new scala.collection.mutable.HashSet[Int]()
        playlists(u) += s

        sim_songs(s) = sim_songs.getOrElse(s, 0.0) + 1.0/n
      }

      for(tuple <- sim_songs){
        val s = tuple._1
        val c = tuple._2
        for(uAndp <- playlists){
          if(!uAndp._2.contains(s)){
            result += ((s,c))
          }
        }
      }
      result
  }