Class: Classifier::Bayes

Inherits:
Object show all
Defined in:
lib/classifier/bayes.rb

Instance Method Summary collapse

Constructor Details

#initialize(*categories) ⇒ Bayes

The class can be created with one or more categories, each of which will be initialized and given a training method. E.g.,

b = Classifier::Bayes.new 'Interesting', 'Uninteresting', 'Spam'



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# File 'lib/classifier/bayes.rb', line 10

def initialize(*categories)
  @categories = {}
  categories.each { |category| @categories[category.prepare_category_name] = {} }
  @total_words = 0
  @category_counts = Hash.new(0)
  @category_word_count = Hash.new(0)
end

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

#method_missing(name, *args) ⇒ Object

Provides training and untraining methods for the categories specified in Bayes#new For example:

b = Classifier::Bayes.new 'This', 'That', 'the_other'
b.train_this "This text"
b.train_that "That text"
b.untrain_that "That text"
b.train_the_other "The other text"



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# File 'lib/classifier/bayes.rb', line 102

def method_missing(name, *args)
  category = name.to_s.gsub(/(un)?train_(\w+)/, '\2').prepare_category_name
  if @categories.key?(category)
    args.each do |text|
      if name.to_s.start_with?('untrain_')
        untrain(category, text)
      else
        train(category, text)
      end
    end
  elsif name.to_s =~ /(un)?train_(\w+)/
    raise StandardError, "No such category: #{category}"
  else
    super
  end
end

Instance Method Details

#add_category(category) ⇒ Object Also known as: append_category

Allows you to add categories to the classifier. For example:

b.add_category "Not spam"

WARNING: Adding categories to a trained classifier will result in an undertrained category that will tend to match more criteria than the trained selective categories. In short, try to initialize your categories at initialization.



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# File 'lib/classifier/bayes.rb', line 137

def add_category(category)
  @categories[category.prepare_category_name] = {}
end

#categories ⇒ Object

Provides a list of category names For example:

b.categories
=>   ['This', 'That', 'the_other']



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# File 'lib/classifier/bayes.rb', line 124

def categories # :nodoc:
  @categories.keys.collect(&:to_s)
end

#classifications(text) ⇒ Object

Returns the scores in each category the provided text. E.g.,

b.classifications "I hate bad words and you"
=>  {"Uninteresting"=>-12.6997928013932, "Interesting"=>-18.4206807439524}

The largest of these scores (the one closest to 0) is the one picked out by #classify



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# File 'lib/classifier/bayes.rb', line 67

def classifications(text)
  score = {}
  word_hash = text.word_hash
  training_count = @category_counts.values.inject { |x, y| x + y }.to_f
  @categories.each do |category, category_words|
    score[category.to_s] = 0
    total = (@category_word_count[category] || 1).to_f
    word_hash.each_key do |word|
      s = category_words.key?(word) ? category_words[word] : 0.1
      score[category.to_s] += Math.log(s / total)
    end
    # now add prior probability for the category
    s = @category_counts.key?(category) ? @category_counts[category] : 0.1
    score[category.to_s] += Math.log(s / training_count)
  end
  score
end

#classify(text) ⇒ Object

Returns the classification of the provided text, which is one of the categories given in the initializer. E.g.,

b.classify "I hate bad words and you"
=>  'Uninteresting'



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# File 'lib/classifier/bayes.rb', line 90

def classify(text)
  (classifications(text).sort_by { |a| -a[1] })[0][0]
end

#remove_category(category) ⇒ Object

Allows you to remove categories from the classifier. For example:

b.remove_category "Spam"

WARNING: Removing categories from a trained classifier will result in the loss of all training data for that category. Make sure you really want to do this before calling this method.

Raises:

  • (StandardError) 


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# File 'lib/classifier/bayes.rb', line 151

def remove_category(category)
  category = category.prepare_category_name
  raise StandardError, "No such category: #{category}" unless @categories.key?(category)

  @total_words -= @category_word_count[category].to_i

  @categories.delete(category)
  @category_counts.delete(category)
  @category_word_count.delete(category)
end

#train(category, text) ⇒ Object

Provides a general training method for all categories specified in Bayes#new For example:

b = Classifier::Bayes.new 'This', 'That', 'the_other'
b.train :this, "This text"
b.train "that", "That text"
b.train "The other", "The other text"



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# File 'lib/classifier/bayes.rb', line 25

def train(category, text)
  category = category.prepare_category_name
  @category_counts[category] += 1
  text.word_hash.each do |word, count|
    @categories[category][word] ||= 0
    @categories[category][word] += count
    @total_words += count
    @category_word_count[category] += count
  end
end

#untrain(category, text) ⇒ Object

Provides a untraining method for all categories specified in Bayes#new Be very careful with this method.

For example:

b = Classifier::Bayes.new 'This', 'That', 'the_other'
b.train :this, "This text"
b.untrain :this, "This text"



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# File 'lib/classifier/bayes.rb', line 44

def untrain(category, text)
  category = category.prepare_category_name
  @category_counts[category] -= 1
  text.word_hash.each do |word, count|
    next unless @total_words >= 0

    orig = @categories[category][word] || 0
    @categories[category][word] ||= 0
    @categories[category][word] -= count
    if @categories[category][word] <= 0
      @categories[category].delete(word)
      count = orig
    end
    @category_word_count[category] -= count if @category_word_count[category] >= count
    @total_words -= count
  end
end