Calculated the mean squared error between data in two files. Files should be single columns of the same length.

meansqerror.rb

#! /home/morgan/bin/ruby/bin/ruby

# Calculates the mean squared error between two data sets
# http://en.wikipedia.org/wiki/Mean_squared_error

# BJM 26/06/13

def check_files_exist( filenames )
  all_files_exist = true
  filenames.each do |filename| 
    unless File.exist?( filename )
      all_files_exist = false
      warn( "#{$executable_name}: #{filename} not found" )
    end
  end
  abort unless all_files_exist
end
  
def read_column_of_data( filename )
  return File.new( filename, 'r' ).readlines.map{ |l| l.to_f }
end

$executable_name = File.basename( $PROGRAM_NAME )

file1 = ARGV[0]
file2 = ARGV[1]

check_files_exist( [file1, file2] )

data1 = read_column_of_data( file1 )
data2 = read_column_of_data( file2 )

if ( data1.size != data2.size )
  abort( "#{$executable_name}: incommensurate data\n#{data1.size} lines in #{file1}\n#{data2.size} lines in #{file2}" ) 
end

puts data1.zip( data2 ).inject(0) { |sum, d| sum + ( d[0] -  d[1] )**2.0 } / data1.size.to_f