The "Best Of" mode uses a percentage ranking of posts.

app/models/post.rb

@@ -157,7 +157,7 @@ class Post < ActiveRecord::Base
   end
 
   def self.best_of
-    where("(post_number = 1) or (score >= ?)", SiteSetting.best_of_score_threshold)
+    where(["(post_number = 1) or (percent_rank <= ?)", SiteSetting.best_of_percent_filter.to_f / 100.0])
   end
 
   def update_flagged_posts_count

app/models/site_setting.rb

@@ -106,6 +106,7 @@ class SiteSetting < ActiveRecord::Base
   setting(:best_of_score_threshold, 15)
   setting(:best_of_posts_required, 50)
   setting(:best_of_likes_required, 1)
+  setting(:best_of_percent_filter, 5)
 
   # we need to think of a way to force users to enter certain settings, this is a minimal config thing
   setting(:notification_email, 'info@discourse.org')

config/locales/server.en.yml

@@ -329,6 +329,7 @@ en:
     best_of_score_threshold: "The minimum score of a post to be included in the 'best of'"
     best_of_posts_required: "Minimum posts in a topic before 'best of' mode is enabled"
     best_of_likes_required: "Minimum likes in a topic before the 'best of' mode will be enabled"
+    best_of_percent_filter: "When a user clicks best of, show the top % of posts"
     enable_private_messages: "Allow trust level 1 users to create private messages and conversations"
 
     enable_long_polling: "Message bus used for notification can use long polling"

config/routes.rb

@@ -171,7 +171,7 @@ Discourse::Application.routes.draw do
   get 'threads/:topic_id/:post_number/avatar' => 'topics#avatar', :constraints => {:topic_id => /\d+/, :post_number => /\d+/}
 
   # Topic routes
-  get 't/:slug/:topic_id/best_of' => 'topics#show', :constraints => {:topic_id => /\d+/, :post_number => /\d+/}
+  get 't/:slug/:topic_id/best_of' => 'topics#show', :defaults => {best_of: true}, :constraints => {:topic_id => /\d+/, :post_number => /\d+/}
   get 't/:topic_id/best_of' => 'topics#show', :constraints => {:topic_id => /\d+/, :post_number => /\d+/}
   put 't/:slug/:topic_id' => 'topics#update', :constraints => {:topic_id => /\d+/}
   put 't/:slug/:topic_id/star' => 'topics#star', :constraints => {:topic_id => /\d+/}

db/migrate/20130322183614_add_percent_rank_to_posts.rb

@@ -0,0 +1,12 @@
+class AddPercentRankToPosts < ActiveRecord::Migration
+  def change
+    add_column :posts, :percent_rank, :float, default: 1.0
+
+    execute "UPDATE posts SET percent_rank = x.percent_rank
+              FROM (SELECT id, percent_rank()
+                    OVER (PARTITION BY topic_id ORDER BY SCORE DESC)
+                    FROM posts) AS x
+              WHERE x.id = posts.id"
+
+  end
+end

lib/score_calculator.rb

@@ -21,6 +21,15 @@ class ScoreCalculator
     # First update the scores of the posts
     exec_sql(post_score_sql, @weightings)
 
+    # Update the percent rankings of the posts
+
+    exec_sql("UPDATE posts SET percent_rank = x.percent_rank
+              FROM (SELECT id, percent_rank()
+                    OVER (PARTITION BY topic_id ORDER BY SCORE DESC) as percent_rank
+                    FROM posts) AS x
+              WHERE x.id = posts.id")
+
+
     # Update the best of flag
     exec_sql "
       UPDATE topics SET has_best_of =
@@ -41,7 +50,7 @@ class ScoreCalculator
 
   private
 
-    def exec_sql(sql, params)
+    def exec_sql(sql, params=nil)
       ActiveRecord::Base.exec_sql(sql, params)
     end
 

spec/components/score_calculator_spec.rb

@@ -3,19 +3,25 @@ require 'score_calculator'
 
 describe ScoreCalculator do
 
-  before do
-    @post = Fabricate(:post, reads: 111)
-    @topic = @post.topic
-  end
+  let!(:post) { Fabricate(:post, reads: 111) }
+  let!(:another_post) { Fabricate(:post, topic: post.topic, reads: 222) }
+  let(:topic) { post.topic }
 
   context 'with weightings' do
     before do
       ScoreCalculator.new(reads: 3).calculate
-      @post.reload
+      post.reload
+      another_post.reload
     end
 
     it 'takes the supplied weightings into effect' do
-      @post.score.should == 333
+      post.score.should == 333
+      another_post.score.should == 666
+    end
+
+    it "creates the percent_ranks" do
+      another_post.percent_rank.should == 0.0
+      post.percent_rank.should == 1.0
     end
   end
 
@@ -23,15 +29,15 @@ describe ScoreCalculator do
 
     it "won't update the site settings when the site settings don't match" do
       ScoreCalculator.new(reads: 3).calculate
-      @topic.reload
-      @topic.has_best_of.should be_false
+      topic.reload
+      topic.has_best_of.should be_false
     end
 
     it "removes the best_of flag if the topic no longer qualifies" do
-      @topic.update_column(:has_best_of, true)
+      topic.update_column(:has_best_of, true)
       ScoreCalculator.new(reads: 3).calculate
-      @topic.reload
-      @topic.has_best_of.should be_false
+      topic.reload
+      topic.has_best_of.should be_false
     end
 
     it "won't update the site settings when the site settings don't match" do
@@ -40,8 +46,8 @@ describe ScoreCalculator do
       SiteSetting.expects(:best_of_score_threshold).returns(100)
 
       ScoreCalculator.new(reads: 3).calculate
-      @topic.reload
-      @topic.has_best_of.should be_true
+      topic.reload
+      topic.has_best_of.should be_true
     end
 
   end

spec/models/post_spec.rb

@@ -628,12 +628,12 @@ describe Post do
   end
 
   context 'best_of' do
-    let!(:p1) { Fabricate(:post, post_args.merge(score: 4)) }
-    let!(:p2) { Fabricate(:post, post_args.merge(score: 10)) }
-    let!(:p3) { Fabricate(:post, post_args.merge(score: 5)) }
+    let!(:p1) { Fabricate(:post, post_args.merge(score: 4, percent_rank: 0.33)) }
+    let!(:p2) { Fabricate(:post, post_args.merge(score: 10, percent_rank: 0.66)) }
+    let!(:p3) { Fabricate(:post, post_args.merge(score: 5, percent_rank: 0.99)) }
 
     it "returns the OP and posts above the threshold in best of mode" do
-      SiteSetting.stubs(:best_of_score_threshold).returns(10)
+      SiteSetting.stubs(:best_of_percent_filter).returns(66)
       Post.best_of.order(:post_number).should == [p1, p2]
     end