word_count.rb

  # Three more ways to cheat:

  # Stack up all the values in a list then sum them at once:
  require 'active_support/core_ext/enumerable'
  class Reducer1 < Wukong::Streamer::ListReducer
    def finalize
      yield [ key, values.map(&:last).map(&:to_i).sum ]
    end
  end

  #
  # ... this is common enough that it's already included
  #
  require 'wukong/streamer/count_keys'
  class Reducer3 < Wukong::Streamer::CountKeys
  end

  #
  # or really cheat
  #
  require 'wukong/streamer/count_keys'
  class Reducer4 < Wukong::Streamer::Base
    def stream
      puts `uniq -c`
    end
  end

word_count_accumulate.rb

  #
  # Accumulate the sum record-by-record:
  #
  class Reducer2 < Wukong::Streamer::AccumulatingReducer
    attr_accessor :key_count
    def start!(*args)      self.key_count =  0 end
    def accumulate(*args)  self.key_count += 1 end
    def finalize
      yield [ key, key_count ]
    end
  end

word_count_accumulate.rb

  #
  # Accumulate the sum record-by-record:
  #
  class Reducer2 < Wukong::Streamer::AccumulatingReducer
    attr_accessor :key_count
    def start!(*args)      self.key_count =  0 end
    def accumulate(*args)  self.key_count += 1 end
    def finalize
      yield [ key, key_count ]
    end
  end

word_count_cheat.rb

module WordCount
  class Mapper < Wukong::Streamer::LineStreamer

    # Split a string into its constituent words.
    def tokenize str
      str.downcase.
        strip.
        split(/\s+/).
        reject(&:blank?)
    end

    # Emit each word in each line.
    def process line
      tokenize(line).each{|word| yield [word, 1] }
    end
  end

  # Conceptually: reduce with uniq -c
end