simple scala functions for cosine similarity

cosine_similarity.scala

/* 
 * Object in scala for calculating cosine similarity
 * Reuben Sutton - 2012
 * More information: http://en.wikipedia.org/wiki/Cosine_similarity
 */
 
object CosineSimilarity {
  
  /*
   * This method takes 2 equal length arrays of integers 
   * It returns a double representing similarity of the 2 arrays
   * 0.9925 would be 99.25% similar
   * (x dot y)/||X|| ||Y||
   */
  def cosineSimilarity(x: Array[Int], y: Array[Int]): Double = {
    require(x.size == y.size)
    dotProduct(x, y)/(magnitude(x) * magnitude(y))
  }
  
  /*
   * Return the dot product of the 2 arrays
   * e.g. (a[0]*b[0])+(a[1]*a[2])
   */
  def dotProduct(x: Array[Int], y: Array[Int]): Int = {
    (for((a, b) <- x zip y) yield a * b) sum
  }
  
  /*
   * Return the magnitude of an array
   * We multiply each element, sum it, then square root the result.
   */
  def magnitude(x: Array[Int]): Double = {
    math.sqrt(x map(i => i*i) sum)
  }
  
}

 def similarity(t1: Map[String, Int], t2: Map[String, Int]): Double = {
     //word, t1 freq, t2 freq
     val m = scala.collection.mutable.HashMap[String, (Int, Int)]()

     val sum1 = t1.foldLeft(0d) {case (sum, (word, freq)) =>
         m += word ->(freq, 0)
         sum + freq
     }

     val sum2 = t2.foldLeft(0d) {case (sum, (word, freq)) =>
         m.get(word) match {
             case Some((freq1, _)) => m += word ->(freq1, freq)
             case None => m += word ->(0, freq)
         }
         sum + freq
     }

     val (p1, p2, p3) = m.foldLeft((0d, 0d, 0d)) {case ((s1, s2, s3), e) =>
         val fs = e._2
         val f1 = fs._1 / sum1
         val f2 = fs._2 / sum2
         (s1 + f1 * f2, s2 + f1 * f1, s3 + f2 * f2)
     }

     val cos = p1 / (Math.sqrt(p2) * Math.sqrt(p3))
     cos
 }