Class: Ai4r::Classifiers::SimpleLinearRegression

Inherits:
Classifier
  • Object
show all
Defined in:
lib/ai4r/classifiers/simple_linear_regression.rb

Overview

Introduction

This is an implementation of a Simple Linear Regression Classifier.

For further details regarding Bayes and Naive Bayes Classifier have a look at this link: en.wikipedia.org/wiki/Naive_Bayesian_classification en.wikipedia.org/wiki/Bayes%27_theorem

How to use it

data = DataSet.new.parse_csv_with_labels "autoPrice.csv"
c = SimpleLinearRegression.new.
  build data
c.eval([1,158,105.8,192.7,71.4,55.7,2844,136,3.19,3.4,8.5,110,5500,19,25])

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods inherited from Classifier

#get_rules

Methods included from Data::Parameterizable

#get_parameters, included, #set_parameters

Constructor Details

#initialize ⇒ SimpleLinearRegression

Returns a new instance of SimpleLinearRegression.



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# File 'lib/ai4r/classifiers/simple_linear_regression.rb', line 38

def initialize
  @attribute = nil
  @attribute_index = 0
  @slope = 0
  @intercept = 0
end

Instance Attribute Details

#attribute ⇒ Object (readonly)

Returns the value of attribute attribute.



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# File 'lib/ai4r/classifiers/simple_linear_regression.rb', line 36

def attribute
  @attribute
end

#attribute_index ⇒ Object (readonly)

Returns the value of attribute attribute_index.



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# File 'lib/ai4r/classifiers/simple_linear_regression.rb', line 36

def attribute_index
  @attribute_index
end

#intercept ⇒ Object (readonly)

Returns the value of attribute intercept.



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# File 'lib/ai4r/classifiers/simple_linear_regression.rb', line 36

def intercept
  @intercept
end

#slope ⇒ Object (readonly)

Returns the value of attribute slope.



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# File 'lib/ai4r/classifiers/simple_linear_regression.rb', line 36

def slope
  @slope
end

Instance Method Details

#build(data) ⇒ Object

Gets the best attribute and does Linear Regression using it to find out the slope and intercept. Parameter data has to be an instance of DataSet



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# File 'lib/ai4r/classifiers/simple_linear_regression.rb', line 56

def build(data)
  raise "Error instance must be passed" unless data.is_a?(DataSet)
  raise "Data should not be empty" if data.data_items.length == 0
  y_mean = data.get_mean_or_mode[data.num_attributes - 1]

  # Choose best attribute
  min_msq = Float::MAX
  attribute = nil
  chosen = -1
  chosen_slope = 0.0 / 0.0 # Float::NAN 
  chosen_intercept = 0.0 / 0.0 # Float::NAN 

  data.data_labels.each do |attr_name|
    attr_index = data.get_index attr_name
    if attr_index != data.num_attributes-1
      # Compute slope and intercept
      x_mean = data.get_mean_or_mode[attr_index]
      sum_x_diff_squared = 0
      sum_y_diff_squared = 0
      slope = 0
      data.data_items.map do |instance|
        x_diff = instance[attr_index] - x_mean
        y_diff = instance[attr_index] - y_mean
        slope += x_diff * y_diff
        sum_x_diff_squared += x_diff * x_diff
        sum_y_diff_squared += y_diff * y_diff
      end

      if sum_x_diff_squared == 0
        next
      end

      numerator = slope
      slope /= sum_x_diff_squared
      intercept = y_mean - slope * x_mean
      msq = sum_y_diff_squared - slope * numerator

      if msq < min_msq
        min_msq = msq
        chosen = attr_index
        chosen_slope = slope
        chosen_intercept = intercept
      end
    end
  end

  if chosen == -1
    raise "no useful attribute found"
    @attribute = nil
    @attribute_index = 0
    @slope = 0
    @intercept = y_mean
  else
    @attribute = data.data_labels[chosen]
    @attribute_index = chosen
    @slope = chosen_slope
    @intercept = chosen_intercept
  end
  return self
end

#eval(data) ⇒ Object

You can evaluate new data, predicting its category. e.g.

c.eval([1,158,105.8,192.7,71.4,55.7,2844,136,3.19,3.4,8.5,110,5500,19,25])
  => 11876.96774193548



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# File 'lib/ai4r/classifiers/simple_linear_regression.rb', line 49

def eval(data)
  @intercept + @slope * data[@attribute_index]
end