Compare Strings By Character Pairs

gistfile1.rb

def compare_strings(str1,str2)
  str1.downcase! 
  pairs1 = (0..str1.length-2).collect {|i| str1[i,2]}.reject { |pair| pair.include? " "}

  str2.downcase! 
  pairs2 = (0..str2.length-2).collect {|i| str2[i,2]}.reject { |pair| pair.include? " "}

  union = pairs1.size + pairs2.size 
  intersection = 0 

  pairs1.each do |p1| 
    0.upto(pairs2.size-1) do |i| 
      if p1 == pairs2[i] 
        intersection += 1 
        pairs2.slice!(i) 
        break 
      end 
    end 
  end 
  (2.0 * intersection) / union
end
# http://www.catalysoft.com/articles/StrikeAMatch.html
# http://stackoverflow.com/questions/653157/a-better-similarity-ranking-algorithm-for-variable-length-strings