Optimize ratings calculation

app/controllers/home_controller.rb

@@ -5,7 +5,7 @@ class HomeController < ApplicationController
   def ratings
     @talks = Talk.ordered_by_rating
     @ratings = Ratings.new
-    @votes_count = TalkPreference.count
+    @votes_count = TalkPreference.this_years.count
   end
 
   def export

app/models/ratings.rb

@@ -1,16 +1,9 @@
 class Ratings
-  @ratings = Hash.new(0)
-
   def initialize
-    ratings = TalkPreference.all.pluck(:talks).reduce(Hash.new(0)) do |result, talks|
-      talks.map(&:to_i).each { |talk| result[talk] += 1 }
-      result
-    end.to_h
-
-    @ratings = Hash.new(0).merge!(ratings)
+    @ratings = {}
   end
 
   def [](id)
-    @ratings[id]
+    @ratings[id] ||= SelectedTalk.where(talk_id: id).count
   end
 end

app/views/home/_talk.html.erb

@@ -1,8 +0,0 @@
-<tr>
-  <td><%= talk.id %></td>
-  <td><%= talk.event_type.name %></td>
-  <td><%= talk.title %></td>
-  <td><%= talk.subtitle %></td>
-  <td><%= @ratings[talk.id] %></td>
-  <td><%= "%.2f%" % Rational(100 * @ratings[talk.id], @votes_count).to_f %></td>
-</tr>

app/views/home/ratings.html.erb

@@ -10,6 +10,15 @@
     </tr>
   </thead>
   <tbody>
-    <%= render partial: 'talk', collection: @talks %>
+    <% @talks.each do |talk| %>
+      <tr>
+        <td><%= talk.id %></td>
+        <td><%= talk.event_type.name %></td>
+        <td><%= talk.title %></td>
+        <td><%= talk.subtitle %></td>
+        <td><%= @ratings[talk.id] %></td>
+        <td><%= "%.2f%" % Rational(100 * @ratings[talk.id], @votes_count).to_f %></td>
+      </tr>
+    <% end %>
   </tbody>
 </table>