Conflict coefficients

app/controllers/home_controller.rb

@@ -11,4 +11,8 @@ class HomeController < ApplicationController
     @talks = Talk.all
     @talk_preferences = TalkPreference.all
   end
+
+  def conflicts
+    @conflict_coefficients = ConflictCoefficient.all
+  end
 end

app/models/conflict_coefficient.rb

@@ -0,0 +1,25 @@
+class ConflictCoefficient
+  attr_reader :left, :right, :conflicts
+
+  def self.all
+    talk_combinations = Talk.all.map(&:id).combination(2)
+    talk_preferences = TalkPreference.all
+    talk_preferences_count = TalkPreference.count
+
+    talk_combinations.map do |talks|
+      conflicts = talk_preferences.select do |talk_preference|
+        talk_preference.include_all? talks
+      end.count
+
+      ConflictCoefficient.new talks.first, talks.last, conflicts, talk_preferences_count
+    end
+  end
+
+  def initialize(left, right, conflicts, total_votes)
+    @left, @right, @conflicts, @total_votes = left, right, conflicts, total_votes
+  end
+
+  def per_cent
+    Rational(100 * @conflicts, @total_votes).to_f
+  end
+end

app/models/talk_preference.rb

@@ -9,6 +9,10 @@ class TalkPreference < ActiveRecord::Base
     talks.include? id.to_s
   end
 
+  def include_all?(ids)
+    ids.all? { |id| include? id }
+  end
+
   private
 
   def assign_new_unique_id

app/views/home/_conflict_coefficient.csv.erb

@@ -0,0 +1 @@
+<%= CSV.generate_line([conflict_coefficient.left, conflict_coefficient.right, conflict_coefficient.conflicts, conflict_coefficient.per_cent]).html_safe -%>

app/views/home/conflicts.csv.erb

@@ -0,0 +1,3 @@
+<%- headers = ['left', 'right', 'conflicts', '%'] -%>
+<%= CSV.generate_line headers -%>
+<%= render partial: 'conflict_coefficient', collection: @conflict_coefficients %>

config/routes.rb

@@ -3,4 +3,5 @@ Rails.application.routes.draw do
   root to: 'home#index'
   get 'ratings' => 'home#ratings'
   get 'export' => 'home#export'
+  get 'conflicts' => 'home#conflicts'
 end