A Ruby class to generate order-2 Markov text.

Markov.rb

#!/usr/bin/env ruby
# 
# Markov.rb
# =========
# 
#   A weighted Markov chain [text] generator implementation in Ruby
#   Actually works! 
# 
# 
# Usage
# =====
# 
#  Markov.new does absolutely nothing of interest. 
# 
#  Markov#add (from, to) adds an association between a word and its likely successor, 
#                        returning nothing of interest.
# 
#  Markov#get (seed, n) returns a string with n length and a starting word of seed.
#                       Both arguments may be omitted and will be randomly generated as 
#                       necessary. By default, n is anywhere between 2 and 22. 
#                       By default, seed is one of the words that have been used for 
#                       associations.
# 
#  weighted_rand (limit) returns a value from 0 to limit that's more likely to be near
#                        0 than the limit. I use this in my weighting as the word lists 
#                        use order to determine most commonly used words. 
# 
#  Well, that's about it.
#  
# by boxmein 2014 - free to use with attribution.
 
 
# 
# something random-like
# however quite determinate
# more-so as weighted
# 
def weighted_rand (limit=1)
	r = rand
	((r ** 2) * limit).to_i
end
 
class Markov
	# 
	# Key value pairs used
	# Providing state and weight as
	# Markov chain order
	#
	
 	attr_accessor :data
 	def initialize
 		@data = Hash.new
 	end

	# 
	# The machine learns now.
	# First key saves second value
	# Let it do its thing.
	# 
	def add (fst, snd)
		# good move?
		fst=fst.to_sym
		
		if @data[fst]
			if @data[fst].index(snd)
				# puts "sent existing #{snd} to front of array"
				
				@data[fst].delete snd
				@data[fst].unshift snd
			else 
				# puts "added #{snd} to end of array"
				@data[fst].push snd
			end
		else
			# puts "new #{fst}: added new array with #{snd}"
			@data[fst] = [snd]
		end
		# for scale
		# p @data
	end
	
	# 
	# there comes a time when
	# even our mightiest database
	# must out a value
	# 
	def get (seed=nil)
		sentence = ""

		# woo, default symbol!
		seed ||= @data.keys.sample
		# we did symbol stuff!
		seed = seed.to_sym

		(Math.log(rand * 10) * 20).to_i.times do |i|
			seed = one_word seed
			sentence += " #{seed}"
		end

		return sentence.strip.squeeze(' ').capitalize + '.'
	end
 
	# 
	# for multiple words
	# a single instance method for
	# proper behaviour
	# 
	def one_word (seed)
		# let's just turn it into a symbol even if it is one
		seed = seed.to_sym
		@data[seed][weighted_rand @data[seed].length]
	end


	# given a file name, create a Markov structure for it
	def self.fromfile (f)
		raise "#{f} does not exist" if not File.exist? f
		raise "#{f} is not a file" if not File.file? f
		raise "#{f} is unavailable to this script" if not File.readable? f

		m = Markov.new
		File.open(f, 'r').each_line do |line|
			line = line.chomp.split
			line.length.times do |i|
				# print i, ': ', line[i], ' -> ',  line[i+1], "\n"

				m.add(line[i], line[i+1]) if line.length > i + 1
			end
		end
		return m
	end

end