Class: ClassifierReborn::Bayes

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

Constant Summary collapse

CategoryNotFoundError = 
Class.new(StandardError)

Instance Method Summary collapse

Constructor Details

#initialize(*args) ⇒ 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 = ClassifierReborn::Bayes.new 'Interesting', 'Uninteresting', 'Spam'

Options available are:

language:         'en'   Used to select language specific stop words
auto_categorize:  false  When true, enables ability to dynamically declare a category
enable_threshold: false  When true, enables a threshold requirement for classifition
threshold:        0.0    Default threshold, only used when enabled



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# File 'lib/classifier-reborn/bayes.rb', line 20

def initialize(*args)
  @categories = Hash.new
  options = { language:         'en', 
              auto_categorize:  false,
              enable_threshold: false,
              threshold:        0.0
            }
  args.flatten.each { |arg|
    if arg.kind_of?(Hash)
      options.merge!(arg)
    else
      add_category(arg)
    end
  }

  @total_words         = 0
  @category_counts     = Hash.new(0)
  @category_word_count = Hash.new(0)

  @language            = options[:language]
  @auto_categorize     = options[:auto_categorize]
  @enable_threshold    = options[:enable_threshold]
  @threshold           = options[:threshold]
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 = ClassifierReborn::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-reborn/bayes.rb', line 174

def method_missing(name, *args)
  cleaned_name = name.to_s.gsub(/(un)?train_([\w]+)/, '\2')
  category = CategoryNamer.prepare_name(cleaned_name)
  if @categories.has_key? category
    args.each { |text| eval("#{$1}train(category, text)") }
  elsif name.to_s =~ /(un)?train_([\w]+)/
    raise StandardError, "No such category: #{category}"
  else
    super  #raise StandardError, "No such method: #{name}"
  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-reborn/bayes.rb', line 202

def add_category(category)
  @categories[CategoryNamer.prepare_name(category)] ||= Hash.new(0)
end

#categories ⇒ Object

Provides a list of category names For example:

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



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# File 'lib/classifier-reborn/bayes.rb', line 190

def categories # :nodoc:
  @categories.keys.collect {|c| c.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-reborn/bayes.rb', line 102

def classifications(text)
  score = Hash.new
  word_hash = Hasher.word_hash(text, @language)
  training_count = @category_counts.values.reduce(:+).to_f
  @categories.each do |category, category_words|
    score[category.to_s] = 0
    total = (@category_word_count[category] || 1).to_f
    word_hash.each do |word, count|
      s = category_words.has_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.has_key?(category) ? @category_counts[category] : 0.1
    score[category.to_s] += Math.log(s / training_count)
  end
  return score
end

#classify(text) ⇒ Object

Return the classification without the score



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# File 'lib/classifier-reborn/bayes.rb', line 129

def classify(text)
  result, score = classify_with_score(text)
  if threshold_enabled?
    result = nil if score < @threshold || score == Float::INFINITY
  end
  return result
end

#classify_with_score(text) ⇒ Object

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

b.classify "I hate bad words and you"
=>  ['Uninteresting', -4.852030263919617]



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

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

#disable_threshold ⇒ Object

Dynamically disable threshold for classify results



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# File 'lib/classifier-reborn/bayes.rb', line 153

def disable_threshold
  @enable_threshold = false
end

#enable_threshold ⇒ Object

Dynamically enable threshold for classify results



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# File 'lib/classifier-reborn/bayes.rb', line 148

def enable_threshold
  @enable_threshold = true
end

#threshold ⇒ Object

Retrieve the current threshold value



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# File 'lib/classifier-reborn/bayes.rb', line 138

def threshold
  @threshold
end

#threshold=(a_float) ⇒ Object

Dynamically set the threshold value



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# File 'lib/classifier-reborn/bayes.rb', line 143

def threshold=(a_float)
  @threshold = a_float
end

#threshold_disabled? ⇒ Boolean

is threshold processing disabled?

Returns:

  • (Boolean) 


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# File 'lib/classifier-reborn/bayes.rb', line 163

def threshold_disabled?
  !@enable_threshold
end

#threshold_enabled? ⇒ Boolean

Is threshold processing enabled?

Returns:

  • (Boolean) 


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# File 'lib/classifier-reborn/bayes.rb', line 158

def threshold_enabled?
  @enable_threshold
end

#train(category, text) ⇒ Object

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

b = ClassifierReborn::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-reborn/bayes.rb', line 51

def train(category, text)
  category = CategoryNamer.prepare_name(category)

  # Add the category dynamically or raise an error
  if !@categories.has_key?(category)
    if @auto_categorize
      add_category(category)
    else
      raise CategoryNotFoundError.new("Cannot train; category #{category} does not exist")
    end
  end

  @category_counts[category] += 1
  Hasher.word_hash(text, @language).each do |word, count|
    @categories[category][word]      +=     count
    @category_word_count[category]   += count
    @total_words += 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 = ClassifierReborn::Bayes.new 'This', 'That', 'the_other'
b.train :this, "This text"
b.untrain :this, "This text"



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# File 'lib/classifier-reborn/bayes.rb', line 78

def untrain(category, text)
  category = CategoryNamer.prepare_name(category)
  @category_counts[category] -= 1
  Hasher.word_hash(text, @language).each do |word, count|
    if @total_words >= 0
      orig = @categories[category][word] || 0
      @categories[category][word]      -=     count
      if @categories[category][word] <= 0
        @categories[category].delete(word)
        count = orig
      end

      if @category_word_count[category] >= count
        @category_word_count[category] -= count
      end
      @total_words -= count
    end
  end
end