Move method to model

app/controllers/exercise_collections_controller.rb

@@ -1,6 +1,5 @@
 class ExerciseCollectionsController < ApplicationController
   include CommonBehavior
-  include TimeHelper
 
   before_action :set_exercise_collection, only: [:show, :edit, :update, :destroy, :statistics]
 
@@ -37,11 +36,6 @@ class ExerciseCollectionsController < ApplicationController
   end
 
   def statistics
-    @working_times = {}
-    @exercise_collection.exercises.each do |exercise|
-      @working_times[exercise.id] = time_to_f exercise.average_working_time
-    end
-    @average = @working_times.values.reduce(:+) / @working_times.size
   end
 
   private

app/models/exercise_collection.rb

@@ -1,8 +1,17 @@
 class ExerciseCollection < ActiveRecord::Base
+  include TimeHelper
 
   has_and_belongs_to_many :exercises
   belongs_to :user, polymorphic: true
 
+  def average_working_time
+    working_times = {}
+    exercises.each do |exercise|
+      working_times[exercise.id] = time_to_f exercise.average_working_time
+    end
+    working_times.values.reduce(:+) / working_times.size
+  end
+
   def to_s
     "#{I18n.t('activerecord.models.exercise_collection.one')}: #{name} (#{id})"
   end

app/views/exercise_collections/statistics.html.slim

@@ -3,4 +3,4 @@ h1 = @exercise_collection
 = row(label: 'exercise_collections.name', value: @exercise_collection.name)
 = row(label: 'exercise_collections.updated_at', value: @exercise_collection.updated_at)
 = row(label: 'exercise_collections.exercises', value: @exercise_collection.exercises.count)
-= row(label: 'exercises.statistics.average_worktime', value: @average.round(3).to_s + 's')
+= row(label: 'exercises.statistics.average_worktime', value: @exercise_collection.average_working_time.round(3).to_s + 's')