added classifier based on Tf-Idf

lib/stuff-classifier.rb

@@ -4,4 +4,5 @@ module StuffClassifier
   autoload :Tokenizer,  'stuff-classifier/tokenizer'
   autoload :Base,       'stuff-classifier/base'
   autoload :Bayes,      'stuff-classifier/bayes'
+  autoload :TfIdf,      'stuff-classifier/tf-idf'
 end

lib/stuff-classifier/tf-idf.rb

@@ -0,0 +1,41 @@
+class StuffClassifier::TfIdf < StuffClassifier::Base
+  def tf_idf(word, cat)
+    word_cat_nr = word_count(word, cat)
+    cat_nr = cat_count(cat)
+    tf = 1.0 * word_cat_nr / cat_nr
+
+    total_categories = categories.length
+    categories_with_word = (@wcount[word] || []).length
+
+    idf = Math.log((total_categories + 2) / (categories_with_word + 1.0), 10)    
+    return tf * idf
+  end
+
+  def text_prob(text, cat)
+    each_word(text).map{|w| tf_idf(w, cat)}.inject(0){|s,p| s + p}
+  end
+
+  def cat_scores(text)
+    probs = {}
+    categories.each do |cat|
+      p = text_prob(text, cat)
+      probs[cat] = p
+    end
+    probs.map{|k,v| [k,v]}.sort{|a,b| b[1] <=> a[1]}
+  end
+
+  def classify(text, default=nil)
+    max_prob = 0.0
+    best = nil
+
+    cat_scores(text).each do |score|
+      cat, prob = score
+      if prob > max_prob
+        max_prob = prob
+        best = cat
+      end
+    end
+
+    max_prob > 0 ? best : default
+  end
+end

test/minitest_helper.rb → test/helper.rb

@@ -17,8 +17,7 @@
  c.natural = true
 end
 
-
-class StuffClassifierTest < MiniTest::Unit::TestCase
+class TestBase < MiniTest::Unit::TestCase
   def self.before(&block)    
     @on_setup = block if block
     @on_setup

test/test_001_tokenizer.rb

@@ -1,7 +1,6 @@
-require 'minitest_helper'
+require 'helper'
 
-
-class Test001Tokenizer < StuffClassifierTest  
+class Test001Tokenizer < TestBase
   before do
     tokenizer_cls = Class.new do
       include StuffClassifier::Tokenizer

test/test_002_naive_bayes.rb

@@ -1,7 +1,7 @@
-require 'minitest_helper'
+require 'helper'
 
 
-class Test002NaiveBayesClassification < StuffClassifierTest  
+class Test002NaiveBayesClassification < TestBase
   before do
     set_classifier StuffClassifier::Bayes.new("Cats or Dogs")
 

test/test_003_tf_idf.rb

@@ -0,0 +1,37 @@
+require 'helper'
+
+
+class Test003TfIdfClassification < TestBase
+  before do
+    set_classifier StuffClassifier::TfIdf.new("Cats or Dogs")
+
+    train :dog, "Dogs are awesome, cats too. I love my dog"
+    train :cat, "Cats are more preferred by software developers. I never could stand cats. I have a dog"    
+    train :dog, "My dog's name is Willy. He likes to play with my wife's cat all day long. I love dogs"
+    train :cat, "Cats are difficult animals, unlike dogs, really annoying, I hate them all"
+    train :dog, "So which one should you choose? A dog, definitely."
+    train :cat, "The favorite food for cats is bird meat, although mice are good, but birds are a delicacy"
+    train :dog, "A dog will eat anything, including birds or whatever meat"
+    train :cat, "My cat's favorite place to purr is on my keyboard"
+    train :dog, "My dog's favorite place to take a leak is the tree in front of our house"
+  end
+
+  def test_for_cats 
+    should_be :cat, "This test is about cats."
+    should_be :cat, "I hate ..."
+    should_be :cat, "The most annoying animal on earth."
+    should_be :cat, "The preferred company of software developers."
+    should_be :cat, "My precious, my favorite!"
+    should_be :cat, "Kill that bird!"
+  end
+
+  def test_for_dogs
+    should_be :dog, "This test is about dogs."
+    should_be :dog, "Cats or Dogs?" 
+    should_be :dog, "What pet will I love more?"    
+    should_be :dog, "Willy, where the heck are you?"
+    should_be :dog, "I like big buts and I cannot lie." 
+    should_be :dog, "Why is the front door of our house open?"
+    should_be :dog, "Who is eating my meat?"
+  end
+end