Ruby script to calculate statistics from CSV data file

timestats.rb

#!/usr/bin/env ruby -n
# usage: ruby timestats.rb < data.csv

BEGIN {
  $data = { real: [], user: [], sys: [] }

  class Array
    def mean
      sum = inject(0) { |s,n| s += n }
      sum.to_f / size
    end

    def median
      if size % 2 == 0
        sort[(size/2)-1, 2].mean
      else
        sort[(size/2)]
      end
    end

    def stddev
      m = mean
      variance = inject(0) { |s,n| s+= (n-m) ** 2 } / (size-1)
      Math.sqrt(variance)
    end
  end
}

END {
  puts "        real    user    sys"
  puts "min    %6.2f %6.2f %6.2f" % $data.values.map(&:min)
  puts "max    %6.2f %6.2f %6.2f" % $data.values.map(&:max)
  puts "mean   %6.2f %6.2f %6.2f" % $data.values.map(&:mean)
  puts "stddev %6.2f %6.2f %6.2f" % $data.values.map(&:stddev)
  puts "median %6.2f %6.2f %6.2f" % $data.values.map(&:median)
}

next unless $_ =~ /^([\d\.]+),([\d\.]+),([\d\.]+)$/
real, user, sys = $1, $2, $3
$data[:real] << real.to_f
$data[:user] << user.to_f
$data[:sys]  << sys.to_f