Extracted similarity calculation logic into a separate class

lib/recommendable/helpers/calculations.rb

@@ -1,3 +1,5 @@
+require_relative 'calculations/similarity'
+
 module Recommendable
   module Helpers
     module Calculations
@@ -12,42 +14,7 @@ class << self
         # @return [Float] the numeric similarity between this user and the passed user
         # @note Similarity values are asymmetrical. `Calculations.similarity_between(user_id, other_user_id)` will not necessarily equal `Calculations.similarity_between(other_user_id, user_id)`
         def similarity_between(user_id, other_user_id)
-          user_id = user_id.to_s
-          other_user_id = other_user_id.to_s
-
-          similarity = liked_count = disliked_count = 0
-          in_common = Recommendable.config.ratable_classes.each do |klass|
-            liked_set = Recommendable::Helpers::RedisKeyMapper.liked_set_for(klass, user_id)
-            other_liked_set = Recommendable::Helpers::RedisKeyMapper.liked_set_for(klass, other_user_id)
-            disliked_set = Recommendable::Helpers::RedisKeyMapper.disliked_set_for(klass, user_id)
-            other_disliked_set = Recommendable::Helpers::RedisKeyMapper.disliked_set_for(klass, other_user_id)
-
-            results = Recommendable.redis.pipelined do
-              # Agreements
-              Recommendable.redis.sinter(liked_set, other_liked_set)
-              Recommendable.redis.sinter(disliked_set, other_disliked_set)
-
-              # Disagreements
-              Recommendable.redis.sinter(liked_set, other_disliked_set)
-              Recommendable.redis.sinter(disliked_set, other_liked_set)
-
-              Recommendable.redis.scard(liked_set)
-              Recommendable.redis.scard(disliked_set)
-            end
-
-            # Agreements
-            similarity += results[0].size
-            similarity += results[1].size
-
-            # Disagreements
-            similarity -= results[2].size
-            similarity -= results[3].size
-
-            liked_count += results[4]
-            disliked_count += results[5]
-          end
-
-          similarity / (liked_count + disliked_count).to_f
+          Similarity.new(user_id, other_user_id).calculate
         end
 
         # Used internally to update the similarity values between this user and all

lib/recommendable/helpers/calculations/similarity.rb

@@ -0,0 +1,72 @@
+module Recommendable
+  module Helpers
+    module Calculations
+      class Similarity
+        attr_reader :user_id, :other_user_id
+
+        def initialize(user_id, other_user_id)
+          @user_id = user_id.to_s
+          @other_user_id = other_user_id.to_s
+          @similarity = 0
+          @liked_count = 0
+          @disliked_count = 0
+        end
+
+        def calculate
+          Recommendable.config.ratable_classes.each do |klass|
+            sets = liked_and_disliked_sets(klass)
+            results = agreements_and_disagreements(*sets)
+            count_agreements_and_disagreements(results)
+            count_liked_and_disliked(results)
+          end
+
+          @similarity /= (@liked_count + @disliked_count).to_f
+        end
+
+        private
+
+        def agreements_and_disagreements(liked_set, other_liked_set, disliked_set, other_disliked_set)
+          Recommendable.redis.pipelined do
+            # Agreements
+            Recommendable.redis.sinter(liked_set, other_liked_set)
+            Recommendable.redis.sinter(disliked_set, other_disliked_set)
+
+            # Disagreements
+            Recommendable.redis.sinter(liked_set, other_disliked_set)
+            Recommendable.redis.sinter(disliked_set, other_liked_set)
+
+            Recommendable.redis.scard(liked_set)
+            Recommendable.redis.scard(disliked_set)
+          end
+        end
+
+        def count_agreements_and_disagreements(results)
+          add_agreements(results)
+          subtract_disagreements(results)
+        end
+
+        def add_agreements(results)
+          @similarity += results[0].size + results[1].size
+        end
+
+        def subtract_disagreements(results)
+          @similarity -= results[2].size + results[3].size
+        end
+
+        def count_liked_and_disliked(results)
+          @liked_count += results[4]
+          @disliked_count += results[5]
+        end
+
+        def liked_and_disliked_sets(klass)
+          liked_set = Recommendable::Helpers::RedisKeyMapper.liked_set_for(klass, user_id)
+          other_liked_set = Recommendable::Helpers::RedisKeyMapper.liked_set_for(klass, other_user_id)
+          disliked_set = Recommendable::Helpers::RedisKeyMapper.disliked_set_for(klass, user_id)
+          other_disliked_set = Recommendable::Helpers::RedisKeyMapper.disliked_set_for(klass, other_user_id)
+
+          return [liked_set, other_liked_set, disliked_set, other_disliked_set]
+        end
+      end
+    end
+  end
+end

test/recommendable/helpers/calculations/similarity_calculation_test.rb

@@ -0,0 +1,59 @@
+$LOAD_PATH.unshift File.expand_path('../../test', __FILE__)
+require 'test_helper'
+
+class SimilarityCalculationTest < MiniTest::Unit::TestCase
+  def setup
+    @user = Factory(:user)
+    5.times  { |x| instance_variable_set(:"@user#{x+1}",  Factory(:user))  }
+    5.times { |x| instance_variable_set(:"@movie#{x+1}", Factory(:movie)) }
+    5.upto(9) { |x| instance_variable_set(:"@movie#{x+1}", Factory(:documentary)) }
+    10.times { |x| instance_variable_set(:"@book#{x+1}",  Factory(:book))  }
+
+    like(@user, [@movie1, @movie2, @movie3, @book4, @book5, @book6])
+    dislike(@user, [@book1, @book2, @book3, @movie4, @movie5, @movie6])
+
+    # @user.similarity_with(@user1) should ==  1.0
+    like(@user1, [@movie1, @movie2, @movie3, @book4, @book5, @book6, @book7, @book8, @movie9, @movie10])
+    dislike(@user1, [@book1, @book2, @book3, @movie4, @movie5, @movie6, @movie7, @movie8, @book9, @book10])
+
+    # @user.similarity_with(@user2) should ==  0.25
+    like(@user2, [@movie1, @movie2, @movie3, @book4, @book5, @book6])
+    like(@user2, [@book1, @book2, @book3])
+
+    # @user.similarity_with(@user3) should ==  0.0
+    like(@user3, [@movie1, @movie2, @movie3])
+    like(@user3, [@book1, @book2, @book3])
+
+    # @user.similarity_with(@user4) should == -0.25
+    like(@user4, [@movie1, @movie2, @movie3])
+    like(@user4, [@book1, @book2, @book3, @movie4, @movie5, @movie6])
+
+    # @user.similarity_with(@user5) should == -1.0
+    dislike(@user5, [@movie1, @movie2, @movie3, @book4, @book5, @book6])
+    like(@user5, [@book1, @book2, @book3, @movie4, @movie5, @movie6])
+  end
+
+  def test_similarity_between_calculates_correctly
+    assert_equal similarity(@user.id, @user1.id), 1.0
+    assert_equal similarity(@user.id, @user2.id), 0.25
+    assert_equal similarity(@user.id, @user3.id), 0
+    assert_equal similarity(@user.id, @user4.id), -0.25
+    assert_equal similarity(@user.id, @user5.id), -1.0
+  end
+
+  def teardown
+    Recommendable.redis.flushdb
+  end
+
+  def similarity(user_id, other_user_id)
+    Recommendable::Helpers::Calculations::Similarity.new(user_id, other_user_id).calculate
+  end
+
+  def like(user, collection)
+    collection.each { |obj| user.like(obj) }
+  end
+
+  def dislike(user, collection)
+    collection.each { |obj| user.dislike(obj) }
+  end
+end

test/recommendable/helpers/calculations_test.rb

@@ -15,30 +15,6 @@ def setup
     # @user.similarity_with(@user1) should ==  1.0
     [@movie1, @movie2, @movie3, @book4, @book5, @book6, @book7, @book8, @movie9, @movie10].each { |obj| @user1.like(obj) }
     [@book1, @book2, @book3, @movie4, @movie5, @movie6, @movie7, @movie8, @book9, @book10].each { |obj| @user1.dislike(obj) }
-
-    # @user.similarity_with(@user2) should ==  0.25
-    [@movie1, @movie2, @movie3, @book4, @book5, @book6].each { |obj| @user2.like(obj) }
-    [@book1, @book2, @book3].each { |obj| @user2.like(obj) }
-
-    # @user.similarity_with(@user3) should ==  0.0
-    [@movie1, @movie2, @movie3].each { |obj| @user3.like(obj) }
-    [@book1, @book2, @book3].each { |obj| @user3.like(obj) }
-
-    # @user.similarity_with(@user4) should == -0.25
-    [@movie1, @movie2, @movie3].each { |obj| @user4.like(obj) }
-    [@book1, @book2, @book3, @movie4, @movie5, @movie6].each { |obj| @user4.like(obj) }
-
-    # @user.similarity_with(@user5) should == -1.0
-    [@movie1, @movie2, @movie3, @book4, @book5, @book6].each { |obj| @user5.dislike(obj) }
-    [@book1, @book2, @book3, @movie4, @movie5, @movie6].each { |obj| @user5.like(obj) }
-  end
-
-  def test_similarity_between_calculates_correctly
-    assert_equal Recommendable::Helpers::Calculations.similarity_between(@user.id, @user1.id), 1.0
-    assert_equal Recommendable::Helpers::Calculations.similarity_between(@user.id, @user2.id), 0.25
-    assert_equal Recommendable::Helpers::Calculations.similarity_between(@user.id, @user3.id), 0
-    assert_equal Recommendable::Helpers::Calculations.similarity_between(@user.id, @user4.id), -0.25
-    assert_equal Recommendable::Helpers::Calculations.similarity_between(@user.id, @user5.id), -1.0
   end
 
   def test_update_recommendations_ignores_rated_items