simple_naive_bayes_classifier.rb

require "forwardable"

module NaiveBayes

  class Class
    extend Forwardable

    attr_reader    :name
    attr_accessor  :frequency
    def_delegators :@likelihood, :[], :[]=

    def initialize(name)
      @name       = name
      @frequency  = 0
      @likelihood = Hash.new(0)
    end
  end

  class Classifier
    attr_reader :classes

    def initialize
      @classes = Hash.new {|h,k| h[k] = NaiveBayes::Class.new(k) }
    end

    def train(c,doc)
      cls = @classes[c]
      cls.frequency += 1 # => 1, 2, 3, 1, 2, 3
      doc.each {|term, freq|
        cls[term] += freq
      }
      cls
    end

    def classify(doc)
      @classes.values.sort_by {|c|
        c.frequency * doc.inject(0) {|likelihood,(term,freq)|
          likelihood + (c[term]) ** freq # => 0, 3, 4, 4, 4, 4, 4, 7, 7, 10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 2
        }
      }.last.name
    end
  end

  class Object
    def initialize(obj)
      @obj = obj
    end

    def freq
      @obj\
        .split(" ")\
        .inject(Hash.new {|h,k| h[k]=0 }) {|doc,term| doc[term] += 1; doc }
    end
  end

  def self._(obj)
    Object.new(obj)
  end

  def self.test
    # data set
    data_set = [
      {
        :class => :mac,
        :body  => "How do I customize my iPod settings?"
      },
      {
        :class => :mac,
        :body  => "How do I set up an AirPort wireless network?"
      },
      {
        :class => :mac,
        :body  => "How do I set up Mac OS X Mail?"
      },
      {
        :class => :windows,
        :body  => "You must be running Microsoft Internet Explorer 5 or later."
      },
      {
        :class => :windows,
        :body  => "You can obtain updates from the Microsoft Download Center."
      },
      {
        :class => :windows,
        :body  => "Get Office Live Basics for your business today."
      }
    ]

    # test set
    test_set = [
      "How do I sync audio and video to my iPod?",
      "We empower your business now!"
    ]

    # training
    classifier = NaiveBayes::Classifier.new
    data_set.map {|data|
      c = data[:class] # => :mac, :mac, :mac, :windows, :windows, :windows
      d = _(data[:body]).freq # => {"do"=>1, "my"=>1, "How"=>1, "iPod"=>1, "customize"=>1, "settings?"=>1, "I"=>1}, {"do"=>1, "AirPort"=>1, "an"=>1, "set"=>1, "up"=>1, "How"=>1, "network?"=>1, "wireless"=>1, "I"=>1}, {"do"=>1, "X"=>1, "set"=>1, "OS"=>1, "Mac"=>1, "up"=>1, "How"=>1, "I"=>1, "Mail?"=>1}, {"running"=>1, "or"=>1, "Internet"=>1, "be"=>1, "later."=>1, "Microsoft"=>1, "Explorer"=>1, "must"=>1, "You"=>1, "5"=>1}, {"Download"=>1, "from"=>1, "updates"=>1, "Center."=>1, "Microsoft"=>1, "can"=>1, "the"=>1, "obtain"=>1, "You"=>1}, {"Get"=>1, "Live"=>1, "business"=>1, "today."=>1, "Basics"=>1, "your"=>1, "Office"=>1, "for"=>1}

      [c,d]
    }.each {|c,doc|
      classifier.train(c,doc) # => #<NaiveBayes::Class:0x3840de8 @name=:mac, @likelihood={"do"=>1, "my"=>1, "How"=>1, "iPod"=>1, "customize"=>1, "settings?"=>1, "I"=>1}, @frequency=1>, #<NaiveBayes::Class:0x3840de8 @name=:mac, @likelihood={"do"=>2, "my"=>1, "set"=>1, "an"=>1, "AirPort"=>1, "up"=>1, "How"=>2, "iPod"=>1, "customize"=>1, "wireless"=>1, "network?"=>1, "settings?"=>1, "I"=>2}, @frequency=2>, #<NaiveBayes::Class:0x3840de8 @name=:mac, @likelihood={"do"=>3, "my"=>1, "X"=>1, "set"=>2, "an"=>1, "AirPort"=>1, "Mac"=>1, "OS"=>1, "up"=>2, "How"=>3, "iPod"=>1, "customize"=>1, "wireless"=>1, "network?"=>1, "settings?"=>1, "I"=>3, "Mail?"=>1}, @frequency=3>, #<NaiveBayes::Class:0x383e8a4 @name=:windows, @likelihood={"running"=>1, "be"=>1, "Internet"=>1, "or"=>1, "later."=>1, "Microsoft"=>1, "You"=>1, "must"=>1, "Explorer"=>1, "5"=>1}, @frequency=1>, #<NaiveBayes::Class:0x383e8a4 @name=:windows, @likelihood={"running"=>1, "updates"=>1, "from"=>1, "Download"=>1, "be"=>1, "Internet"=>1, "or"=>1, "later."=>1, "can"=>1, "Center."=>1, "Microsoft"=>2, "the"=>1, "obtain"=>1, "You"=>2, "must"=>1, "Explorer"=>1, "5"=>1}, @frequency=2>, #<NaiveBayes::Class:0x383e8a4 @name=:windows, @likelihood={"Get"=>1, "Live"=>1, "business"=>1, "running"=>1, "updates"=>1, "from"=>1, "Download"=>1, "be"=>1, "Internet"=>1, "or"=>1, "later."=>1, "can"=>1, "Center."=>1, "Microsoft"=>2, "today."=>1, "the"=>1, "Basics"=>1, "Office"=>1, "your"=>1, "for"=>1, "obtain"=>1, "You"=>2, "must"=>1, "Explorer"=>1, "5"=>1}, @frequency=3>
    }

    # testing
    test_set.each {|data|
      data # => "How do I sync audio and video to my iPod?", "We empower your business now!"
      cls = classifier.classify _(data).freq # => :mac, :windows
      puts cls
    }
  end
end

NaiveBayes::test

# >> mac
# >> windows