gistfile1.rb

#!/usr/bin/env ruby

# Basic Statistical Methods Module
# accepts: an array, the population/list
# returns: Result of running the measure (std_dev, mean, median)
#
module StatisticalTools
  def self.std_dev(population)
    n    = 0
    mean = 0.0
    s    = 0.0

    population.each do |x|
      n     = n + 1
      delta = x - mean
      mean  = mean + (delta / n)
      s     = s + delta * (x - mean)
    end

    Math.sqrt(s/n)
  end

  def self.mean(list)
    Float (list.inject {|sum, i| sum += i } / list.size)
  end

  def self.median(list)
    list.sort!
    n = (list.length - 1) / 2
    n2 = (list.length) / 2

    list.length % 2 == 0 ? (list[n] + list[n2]) / 2 : list[n]
  end

  def self.sum(list)  
    list.inject( nil ) { |sum,x| sum ? sum+x : x };  
  end 
end

#
# Main
#
if !$test && __FILE__ == $0
  puts "Great running ..."

# Tests
elsif __FILE__ == $0
 require 'test/unit'
  class Test_StatisticalTools < Test::Unit::TestCase
    def setup
      @list_even  = %w(2 4 4 4 5 5 7 9).map {|i| i.to_f}
      @list_odd   = %w(1 3 24 17 12 6 14).map {|i| i.to_f}
      @list_other = %w(1 2 3 4 5).map {|i| i.to_f}
    end

    def two_two(float_n)
      sprintf("%2.2f", float_n)
    end

    def test_mean
      assert_equal(5.00, StatisticalTools::mean(@list_even))
    end

    def test_std_dev
      assert_equal(2, StatisticalTools::std_dev(@list_even))
      assert_equal("7.60", two_two(StatisticalTools::std_dev(@list_odd)))
    end

    def test_median
      assert_equal(2, StatisticalTools::std_dev(@list_even))
    end
  end
end