Mapper & Reducer in ruby

mapper.rb

# Ruby code for map.rb

ARGF.each do |line|

   # remove any newline
   line = line.chomp

   # do nothing will lines shorter than 2 characters
   next if ! line || line.length < 2

   # grab our key as the two-character prefix (lower-cased)
   key = line[0,2].downcase

   # value is a count of 1 occurence
   value = 1

   # output to STDOUT
   # <key><tab><value><newline>
   puts key + "\t" + value.to_s

end

reducer.rb

# Ruby code for reduce.rb

prev_key = nil
key_total = 0

ARGF.each do |line|

   # remove any newline
   line = line.chomp

   # split key and value on tab character
   (key, value) = line.split(/\t/)

   # check for new key
   if prev_key && key != prev_key && key_total > 0

      # output total for previous key

      # <key><tab><value><newline>
      puts prev_key + "\t" + key_total.to_s

      # reset key total for new key
      prev_key = key
      key_total = 0

   elsif ! prev_key
      prev_key = key

   end

   # add to count for this current key
   key_total += value.to_i

end