bi-grams comparison algorithm

gistfile1.rb

  def string_similarity(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