Class: NaiveBayes::Classifier

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

Instance Method Summary collapse

Constructor Details

#initialize(params) ⇒ Classifier

Returns a new instance of Classifier.



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# File 'lib/naivebayes/classifier.rb', line 6

def initialize(params)
  @frequency_table = Hash.new
  @word_table = Hash.new
  @instance_count_of = Hash.new(0)
  @total_count = 0
  @model = params[:model]
end

Instance Method Details

#classify(attributes) ⇒ Object 



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# File 'lib/naivebayes/classifier.rb', line 30

def classify(attributes)
  class_prior_of = Hash.new(1)
  likelihood_of = Hash.new(1)
  class_posterior_of = Hash.new(1)
  evidence = 0
  @instance_count_of.each {|label, freq|
    class_prior_of[label] = freq.to_f / @total_count.to_f
  }
  @frequency_table.each_key {|label|
    likelihood_of[label] = 1
    @word_table.each_key {|word|
      laplace_word_likelihood = (@frequency_table[label][word] + 1).to_f /
        (@instance_count_of[label] + @word_table.size()).to_f
      if attributes.has_key?(word)
        likelihood_of[label] *= laplace_word_likelihood
      else
        likelihood_of[label] *= (1 - laplace_word_likelihood)
      end
    }
    class_posterior_of[label] = class_prior_of[label] * likelihood_of[label]
    evidence += class_posterior_of[label]
  }
  class_posterior_of.each {|label, posterior|
    class_posterior_of[label] = posterior / evidence
  }
  return class_posterior_of
end

#train(label, attributes) ⇒ Object 



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# File 'lib/naivebayes/classifier.rb', line 14

def train(label, attributes)
  unless @frequency_table.has_key?(label)
    @frequency_table[label] = Hash.new(0)
  end
  attributes.each {|word, frequency|
    if @model == "multinomial"
      @frequency_table[label][word] += frequency
    else
      @frequency_table[label][word] += 1
    end
    @word_table[word] = 1
  }
  @instance_count_of[label] += 1
  @total_count += 1
end