half-ass implementation of linear regression in Ruby

linear_regression.rb

#! /usr/bin/env ruby

class LinearRegression
  attr_reader :coords, :size

  def initialize(coords)
    @coords = coords
    @size = coords.size
  end

  def xs
    coords.map(&:first)
  end

  def ys
    coords.map(&:last)
  end

  def mean_x
    @mean_x ||= xs.inject(:+) / size
  end

  def mean_y
    @mean_y ||= ys.inject(:+) / size
  end

  def a
    mean_y - b * mean_x
  end

  def b
    num = 0.0
    denom = 0.0

    coords.each do |x, y|
      num += (x - mean_x) * (y - mean_y)
      denom += (x - mean_x) ** 2
    end

    num / denom
  end

  def r
    num = 0.0
    denom1 = 0.0
    denom2 = 0.0

    coords.each do |x, y|
      num += (x - mean_x) * (y - mean_y)
      denom1 += (x - mean_x) ** 2
      denom2 += (y - mean_y) ** 2
    end

    num / (denom1 * denom2) ** 0.5
  end
end