gistfile1.scala

// Scala implementation of simple linear regression as implemented in Ruby
// in the blog post: http://www.sharethrough.com/2012/09/linear-regression-using-ruby/

import scala.io.Source

class SimpleLinearRegression(xs: Seq[Double], ys: Seq[Double]) {
  require(xs.size == ys.size, "xs and ys must be same length")

  def mean(values: Seq[Double]): Double = values.sum / values.size

  def slope: Double = {
    val xmean = mean(xs)
    val ymean = mean(ys)

    val numerator = xs.zip(ys).foldLeft(0.0) { case (sum, (x, y)) =>
      sum + ((x - xmean) * (y - ymean))
    }
    val denominator = xs.foldLeft(0.0) { (sum, x) =>
      sum + math.pow(x - xmean, 2)
    }

    numerator / denominator
  }

  def yIntercept: Double = mean(ys) - (slope * mean(xs))
}

object Runner {
  def main(args: Array[String]) {
    val (xs, ys) = Source.fromFile(args(0)).getLines.toSeq.drop(1).map { line =>
      val Array(x, y) = line.split(',').map { _.toDouble }
      (x, y)
    }.unzip

    val linearModel = new SimpleLinearRegression(xs, ys)
    println("Model generated with")
    println(s"Slope: ${linearModel.slope}")
    println(s"Y-Intercept: ${linearModel.yIntercept}")
    println("\n")
    println("Estimated Linear Model:")
    println(s"Y = ${linearModel.yIntercept} + (${linearModel.slope} * X)")
  }
}