Entropy

entropy.scala

  private def entropy(counts: Vector[Long], totalCount: Double): Double = {
    if (totalCount == 0) {
      return 0
    }

    def log2(x: Double) = scala.math.log(x) / scala.math.log(2)
    counts.filter(_ != 0).map { count =>
      val freq = 1.0 * count / totalCount
      freq * log2(freq)
    }.foldLeft(0.0) { case (agg, i) => agg - i }
  }