markov-chains.rb

# Partial code from Dominik on Ruby Quiz
# http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/188420

class MarkovChainer
  attr_reader :order
  def initialize(order)
    @order = order
    @beginnings = []
    @freq = {}
  end

  def add_text(text)
  # make sure each paragraph ends with some sentence terminator
    text.gsub!(/\n\s*\n/m, ".")
    text << "."
    seps = /([.!?])/
    sentence = ""
    text.split(seps).each { |p|
      if seps =~ p
        add_sentence(sentence, p)
        sentence = ""
      else
        sentence = p
      end
    }
  end

  def generate_sentence
    res = @beginnings[rand(@beginnings.size)]
    loop {
      unless nw = next_word_for(res[-order, order])
        return res[0..-2].join(" ") + res.last
      end
      res << nw
    }
  end

	private

  def add_sentence(str, terminator)
    words = str.scan(/[\w']+/)
    return unless words.size > order # ignore short sentences
    words << terminator
    buf = []
    words.each { |w|
      buf << w
      if buf.size == order + 1
        (@freq[buf[0..-2]] ||= []) << buf[-1]
        buf.shift
      end
    }
    @beginnings << words[0, order]
  end

  def next_word_for(words)
    arr = @freq[words]
    arr && arr[rand(arr.size)]
  end

end