move vote similarity code into danbooru, add listing for super voters

app/logical/post_vote_similarity.rb

@@ -0,0 +1,58 @@
+require "set"
+
+class PostVoteSimilarity
+  class Element
+    attr_reader :user_id, :score
+
+    def initialize(user_id, score)
+      @user_id = user_id
+      @score = score
+    end
+
+    def <=>(rhs)
+      score <=> rhs.score
+    end
+  end
+
+  attr_reader :user_id
+
+  def initialize(user_id)
+    @user_id = user_id
+  end
+
+  # returns user ids with strong negative correlation
+  def calculate_negative(limit = 10)
+    posts0 = PostVote.negative_post_ids(user_id)
+    set = SortedSet.new
+
+    PostVote.positive_user_ids.each do |uid|
+      posts1 = PostVote.positive_post_ids(uid)
+      set.add(Element.new(uid, calculate_with_cosine(posts0, posts1)))
+    end
+
+    set.first(limit)
+  end
+
+  # returns user ids with strong positive correlation
+  def calculate_positive(limit = 10)
+    posts0 = PostVote.positive_post_ids(user_id)
+    set = SortedSet.new
+
+    PostVote.positive_user_ids.each do |uid|
+      posts1 = PostVote.positive_post_ids(uid)
+      set.add(Element.new(uid, calculate_with_cosine(posts0, posts1)))
+    end
+
+    set.first(limit)
+  end
+
+  def calculate_with_cosine(posts0, posts1)
+    a = (posts0 & posts1).size
+    div = Math.sqrt(posts0.size * posts1.size)
+    if div == 0
+      0
+    else
+      a / div
+    end
+  end
+end