Initial version of VNS algorithm (#8)

Reviewed-on: #8
Co-authored-by: Manuel Bustillo <bustikiller@bustikiller.com>
Co-committed-by: Manuel Bustillo <bustikiller@bustikiller.com>

Gemfile

@@ -50,6 +50,7 @@ group :development, :test do
   gem 'rspec-rails', '~> 6.1.0'
   gem 'faker'
   gem 'pry'
+  gem "factory_bot_rails"
 end
 
 group :development do
@@ -65,4 +66,5 @@ end
 
 gem "money"
 gem 'acts-as-taggable-on'
-gem "rubytree"
+
+gem "rubytree"

Gemfile.lock

@@ -94,8 +94,12 @@ GEM
     diff-lcs (1.5.1)
     drb (2.2.1)
     erubi (1.13.0)
-    faker (3.4.2)
-      i18n (>= 1.8.11, < 2)
+    factory_bot (6.4.6)
+      activesupport (>= 5.0.0)
+    factory_bot_rails (6.4.3)
+      factory_bot (~> 6.4)
+      railties (>= 5.0.0)
+    faker (3.1.1)
     globalid (1.2.1)
       activesupport (>= 6.1)
     i18n (1.14.5)
@@ -265,6 +269,7 @@ DEPENDENCIES
   acts-as-taggable-on
   bootsnap
   debug
+  factory_bot_rails
   faker
   importmap-rails
   jbuilder

app/controllers/tables_arrangements_controller.rb

@@ -0,0 +1,10 @@
+class TablesArrangementsController < ApplicationController
+  def index
+    @tables_arrangements = TablesArrangement.all.order(discomfort: :asc).limit(10)
+  end
+
+  def show
+    @tables_arrangement = TablesArrangement.find(params[:id])
+    @seats = @tables_arrangement.seats.includes(:guest).group_by(&:table_number)
+  end
+end

app/helpers/tables_arrangements_helper.rb

@@ -0,0 +1,2 @@
+module TablesArrangementsHelper
+end

app/models/seat.rb

@@ -0,0 +1,4 @@
+class Seat < ApplicationRecord
+  belongs_to :guest
+  belongs_to :table_arrangement
+end

app/models/tables_arrangement.rb

@@ -0,0 +1,3 @@
+class TablesArrangement < ApplicationRecord
+  has_many :seats
+end

app/services/tables/discomfort_calculator.rb

@@ -0,0 +1,25 @@
+module Tables
+  class DiscomfortCalculator
+    private attr_reader :table
+    def initialize(table)
+      @table = table
+    end
+
+    def calculate
+      cohesion_penalty
+    end
+
+    private
+
+    def cohesion_penalty
+      table.map { |guest| guest.affinity_group_list.first }.tally.to_a.combination(2).sum do |(a, count_a), (b, count_b)|
+        distance = AffinityGroupsHierarchy.instance.distance(a, b)
+
+        next count_a * count_b if distance.nil?
+        next 0 if distance.zero?
+
+        count_a * count_b * Rational(distance, distance + 1)
+      end
+    end
+  end
+end

app/services/tables/distribution.rb

@@ -0,0 +1,64 @@
+require_relative '../../extensions/tree_node_extension'
+
+module Tables
+  class Distribution
+    attr_accessor :tables
+
+    def initialize(min_per_table:, max_per_table:)
+      @min_per_table = min_per_table
+      @max_per_table = max_per_table
+    end
+
+    def random_distribution(people)
+      @tables = []
+
+      @tables << people.slice!(0..rand(@min_per_table..@max_per_table)) while people.any?
+    end
+
+    def discomfort
+      @tables.map do |table|
+        local_discomfort(table)
+      end.sum
+    end
+
+    def inspect
+      "#{@tables.count} tables, discomfort: #{discomfort}"
+    end
+
+    def pretty_print
+      @tables.map.with_index do |table, i|
+        "Table #{i + 1} (#{table.count} ppl): (#{local_discomfort(table)}) #{table.map(&:full_name).join(', ')}"
+      end.join("\n")
+    end
+
+    def deep_dup
+      self.class.new(min_per_table: @min_per_table, max_per_table: @max_per_table).tap do |new_distribution|
+        new_distribution.tables = @tables.map(&:dup)
+      end
+    end
+
+    def save!
+      ActiveRecord::Base.transaction do
+        arrangement = TablesArrangement.create!
+
+        records_to_store = []
+
+        tables.each_with_index do |table, table_number|
+          table.each do |person|
+            records_to_store << { guest_id: person.id, tables_arrangement_id: arrangement.id, table_number: }
+          end
+        end
+
+        Seat.insert_all!(records_to_store)
+
+        arrangement.update!(discomfort:)
+      end
+    end
+
+    private
+
+    def local_discomfort(table)
+      DiscomfortCalculator.new(table).calculate
+    end
+  end
+end

app/services/tables/swap.rb

@@ -0,0 +1,28 @@
+module Tables
+  class Swap
+    private attr_reader :initial_solution
+    def initialize(initial_solution)
+      @initial_solution = initial_solution
+    end
+
+    def each
+      @initial_solution.tables.combination(2) do |table_a, table_b|
+        table_a.product(table_b).each do |(person_a, person_b)|
+          table_a.delete(person_a)
+          table_b.delete(person_b)
+
+          table_a << person_b
+          table_b << person_a
+
+          yield(@initial_solution)
+        ensure
+          table_a.delete(person_b)
+          table_b.delete(person_a)
+
+          table_a << person_a
+          table_b << person_b
+        end
+      end
+    end
+  end
+end

app/services/vns/engine.rb

@@ -0,0 +1,48 @@
+module VNS
+  class Engine
+    def target_function(&function)
+      @target_function = function
+    end
+
+    def add_perturbation(klass)
+      @perturbations ||= Set.new
+      @perturbations << klass
+    end
+
+    attr_writer :initial_solution
+
+    def run
+      raise 'No target function defined' unless @target_function
+      raise 'No perturbations defined' unless @perturbations
+      raise 'No initial solution defined' unless @initial_solution
+
+      @best_solution = @initial_solution
+      @best_score = @target_function.call(@best_solution)
+
+      puts "Initial score: #{@best_score.to_f}"
+
+      @perturbations.each do |perturbation|
+        puts "Running perturbation: #{perturbation.name}"
+        optimize(perturbation.new(@best_solution))
+      end
+
+      @best_solution 
+    end
+
+    private
+
+    def optimize(perturbation)
+      perturbation.each do |alternative_solution|
+        score = @target_function.call(alternative_solution)
+        next if score >= @best_score
+
+        @best_solution = alternative_solution.deep_dup
+        @best_score = score
+
+        puts "New lowest score: #{@best_score.to_f}"
+
+        return optimize(perturbation.class.new(@best_solution))
+      end
+    end
+  end
+end

app/views/tables_arrangements/index.html.erb

@@ -0,0 +1,9 @@
+<h1>Tables arrangements</h1>
+
+<ol>
+    <% @tables_arrangements.each_with_index do |tables_arrangement, i| %>
+        <li>
+            <p><%= link_to "Arrangement ##{i+1}", tables_arrangement_path(tables_arrangement) %> Discomfort: <%= tables_arrangement.discomfort %></p>
+        </li>
+    <% end %>
+</ol>

app/views/tables_arrangements/show.html.erb

@@ -0,0 +1,16 @@
+<h1>ID: <%= @tables_arrangement.id %></h1>
+
+<p>Discomfort: <%= @tables_arrangement.discomfort %></p>
+
+<h2>Seats</h2>
+
+<% @seats.each do |table_number, seats| %>
+
+  <h3>Table <%= table_number %></h3>
+
+  <ul>
+    <% seats.each do |seat| %>
+      <li><%= seat.guest.full_name %></li>
+    <% end %>
+  </ul>
+<% end %>

config/initializers/inflections.rb

@@ -11,6 +11,6 @@
 # end
 
 # These inflection rules are supported but not enabled by default:
-# ActiveSupport::Inflector.inflections(:en) do |inflect|
-#   inflect.acronym "RESTful"
-# end
+ActiveSupport::Inflector.inflections(:en) do |inflect|
+  inflect.acronym 'VNS'
+end

config/routes.rb

@@ -3,12 +3,7 @@ Rails.application.routes.draw do
     post :import, on: :collection
   end
   resources :expenses
-  # Define your application routes per the DSL in https://guides.rubyonrails.org/routing.html
+  resources :tables_arrangements, only: [:index, :show]
 
-  # Reveal health status on /up that returns 200 if the app boots with no exceptions, otherwise 500.
-  # Can be used by load balancers and uptime monitors to verify that the app is live.
-  get "up" => "rails/health#show", as: :rails_health_check
-
-  # Defines the root path route ("/")
-  # root "posts#index"
+  get 'up' => 'rails/health#show', as: :rails_health_check
 end

db/migrate/20240724181756_create_tables_arrangements.rb

@@ -0,0 +1,9 @@
+class CreateTablesArrangements < ActiveRecord::Migration[7.1]
+  def change
+    create_table :tables_arrangements, id: :uuid do |t|
+      t.integer :discomfort
+
+      t.timestamps
+    end
+  end
+end

db/migrate/20240724181853_create_seats.rb

@@ -0,0 +1,13 @@
+class CreateSeats < ActiveRecord::Migration[7.1]
+  def change
+    create_table :seats, id: :uuid do |t|
+      t.references :guest, null: false, foreign_key: true, type: :uuid
+      t.references :tables_arrangement, null: false, type: :uuid
+      t.integer :table_number
+
+      t.timestamps
+    end
+
+    add_foreign_key :seats, :tables_arrangements, on_delete: :cascade
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.1].define(version: 2024_07_11_181632) do
+ActiveRecord::Schema[7.1].define(version: 2024_07_24_181853) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
 
@@ -35,6 +35,22 @@ ActiveRecord::Schema[7.1].define(version: 2024_07_11_181632) do
     t.datetime "updated_at", null: false
   end
 
+  create_table "seats", id: :uuid, default: -> { "gen_random_uuid()" }, force: :cascade do |t|
+    t.uuid "guest_id", null: false
+    t.uuid "tables_arrangement_id", null: false
+    t.integer "table_number"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["guest_id"], name: "index_seats_on_guest_id"
+    t.index ["tables_arrangement_id"], name: "index_seats_on_tables_arrangement_id"
+  end
+
+  create_table "tables_arrangements", id: :uuid, default: -> { "gen_random_uuid()" }, force: :cascade do |t|
+    t.integer "discomfort"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+  end
+
   create_table "taggings", force: :cascade do |t|
     t.bigint "tag_id"
     t.string "taggable_type"
@@ -66,5 +82,7 @@ ActiveRecord::Schema[7.1].define(version: 2024_07_11_181632) do
     t.index ["name"], name: "index_tags_on_name", unique: true
   end
 
+  add_foreign_key "seats", "guests"
+  add_foreign_key "seats", "tables_arrangements", on_delete: :cascade
   add_foreign_key "taggings", "tags"
 end

db/seeds.rb

@@ -1,13 +1,6 @@
-# This file should ensure the existence of records required to run the application in every environment (production,
-# development, test). The code here should be idempotent so that it can be executed at any point in every environment.
-# The data can then be loaded with the bin/rails db:seed command (or created alongside the database with db:setup).
-#
-# Example:
-#
-#   ["Action", "Comedy", "Drama", "Horror"].each do |genre_name|
-#     MovieGenre.find_or_create_by!(name: genre_name)
-#   end
+NUMBER_OF_GUESTS = 50
 
+TablesArrangement.delete_all
 Expense.delete_all
 Guest.delete_all
 ActsAsTaggableOn::Tagging.delete_all
@@ -53,7 +46,7 @@ samples = {
   count.times { acc << affinity_group }
 end
 
-300.times do
+NUMBER_OF_GUESTS.times do
   guest = Guest.create!(first_name: Faker::Name.first_name,
                         last_name: Faker::Name.last_name,
                         email: Faker::Internet.email,

lib/tasks/vns.rake

@@ -0,0 +1,18 @@
+namespace :vns do
+  task distribute_tables: :environment do
+    engine = VNS::Engine.new
+
+    engine.add_perturbation(Tables::Swap)
+
+    initial_solution = Tables::Distribution.new(min_per_table: 8, max_per_table: 10)
+    initial_solution.random_distribution(Guest.all.shuffle)
+
+    engine.initial_solution = initial_solution
+
+    engine.target_function(&:discomfort)
+
+    best_solution = engine.run
+
+    best_solution.save!
+  end
+end

spec/factories/guest.rb

@@ -0,0 +1,8 @@
+FactoryBot.define do
+  factory :guest do
+    first_name { Faker::Name.first_name }
+    last_name { Faker::Name.last_name }
+    email { Faker::Internet.email }
+    phone { Faker::PhoneNumber.cell_phone }
+  end
+end

spec/models/seat_spec.rb

@@ -0,0 +1,5 @@
+require 'rails_helper'
+
+RSpec.describe Seat, type: :model do
+  pending "add some examples to (or delete) #{__FILE__}"
+end

spec/models/tables_arrangement_spec.rb

@@ -0,0 +1,5 @@
+require 'rails_helper'
+
+RSpec.describe TablesArrangement, type: :model do
+  pending "add some examples to (or delete) #{__FILE__}"
+end

spec/rails_helper.rb

@@ -62,4 +62,5 @@ RSpec.configure do |config|
   config.filter_rails_from_backtrace!
   # arbitrary gems may also be filtered via:
   # config.filter_gems_from_backtrace("gem name")
+  config.include FactoryBot::Syntax::Methods
 end

spec/services/tables/discomfort_calculator_spec.rb

@@ -0,0 +1,158 @@
+require 'rails_helper'
+module Tables
+  RSpec.describe DiscomfortCalculator do
+    let(:calculator) { described_class.new(table) }
+
+    describe '#cohesion_penalty' do
+      before do
+        # Overridden in each test except trivial cases
+        allow(AffinityGroupsHierarchy.instance).to receive(:distance).and_call_original
+
+        %w[family friends work school].each do |group|
+          allow(AffinityGroupsHierarchy.instance).to receive(:distance).with(group, group).and_return(0)
+        end
+
+        allow(AffinityGroupsHierarchy.instance).to receive(:distance).with('family', 'friends').and_return(nil)
+        allow(AffinityGroupsHierarchy.instance).to receive(:distance).with('friends', 'work').and_return(1)
+        allow(AffinityGroupsHierarchy.instance).to receive(:distance).with('family', 'work').and_return(2)
+        allow(AffinityGroupsHierarchy.instance).to receive(:distance).with('family', 'school').and_return(3)
+        allow(AffinityGroupsHierarchy.instance).to receive(:distance).with('friends', 'school').and_return(4)
+        allow(AffinityGroupsHierarchy.instance).to receive(:distance).with('work', 'school').and_return(5)
+      end
+      context 'when the table contains just two guests' do
+        context 'when they belong to the same group' do
+          let(:table) { create_list(:guest, 2, affinity_group_list: ['family']) }
+
+          it { expect(calculator.send(:cohesion_penalty)).to eq(0) }
+        end
+
+        context 'when they belong to completely unrelated groups' do
+          let(:table) do
+            [
+              create(:guest, affinity_group_list: ['family']),
+              create(:guest, affinity_group_list: ['friends'])
+            ]
+          end
+          it { expect(calculator.send(:cohesion_penalty)).to eq(1) }
+        end
+
+        context 'when they belong to groups at a distance of 1' do
+          let(:table) do
+            [
+              create(:guest, affinity_group_list: ['friends']),
+              create(:guest, affinity_group_list: ['work'])
+            ]
+          end
+
+          it { expect(calculator.send(:cohesion_penalty)).to eq(0.5) }
+        end
+
+        context 'when they belong to groups at a distance of 2' do
+          let(:table) do
+            [
+              create(:guest, affinity_group_list: ['family']),
+              create(:guest, affinity_group_list: ['work'])
+            ]
+          end
+
+          it { expect(calculator.send(:cohesion_penalty)).to eq(Rational(2, 3)) }
+        end
+
+        context 'when they belong to groups at a distance of 3' do
+          let(:table) do
+            [
+              create(:guest, affinity_group_list: ['family']),
+              create(:guest, affinity_group_list: ['school'])
+            ]
+          end
+
+          it { expect(calculator.send(:cohesion_penalty)).to eq(Rational(3, 4)) }
+        end
+      end
+
+      context 'when the table contains three guests' do
+        let(:table) do
+          [
+            create(:guest, affinity_group_list: ['family']),
+            create(:guest, affinity_group_list: ['friends']),
+            create(:guest, affinity_group_list: ['work'])
+          ]
+        end
+
+        it 'returns the sum of the penalties for each pair of guests' do
+          expect(calculator.send(:cohesion_penalty)).to eq(1 + Rational(1, 2) + Rational(2, 3))
+        end
+      end
+
+      context 'when the table contains four guests of different groups' do
+        let(:table) do
+          [
+            create(:guest, affinity_group_list: ['family']),
+            create(:guest, affinity_group_list: ['friends']),
+            create(:guest, affinity_group_list: ['work']),
+            create(:guest, affinity_group_list: ['school'])
+          ]
+        end
+
+        it 'returns the sum of the penalties for each pair of guests' do
+          expect(calculator.send(:cohesion_penalty))
+            .to eq(1 + Rational(1, 2) + Rational(2, 3) + Rational(3, 4) + Rational(4, 5) + Rational(5, 6))
+        end
+      end
+
+      context 'when the table contains four guests of two evenly split groups' do
+        let(:table) do
+          [
+            create_list(:guest, 2, affinity_group_list: ['family']),
+            create_list(:guest, 2, affinity_group_list: ['friends'])
+          ].flatten
+        end
+
+        it 'returns the sum of the penalties for each pair of guests' do
+          expect(calculator.send(:cohesion_penalty)).to eq(4)
+        end
+      end
+
+      context 'when the table contains six guests of two unevenly split groups' do
+        let(:table) do
+          [
+            create_list(:guest, 2, affinity_group_list: ['family']),
+            create_list(:guest, 4, affinity_group_list: ['friends'])
+          ].flatten
+        end
+
+        it 'returns the sum of the penalties for each pair of guests' do
+          expect(calculator.send(:cohesion_penalty)).to eq(8)
+        end
+      end
+
+      context 'when the table contains six guests of three evenly split groups' do
+        let(:table) do
+          [
+            create_list(:guest, 2, affinity_group_list: ['family']),
+            create_list(:guest, 2, affinity_group_list: ['friends']),
+            create_list(:guest, 2, affinity_group_list: ['work'])
+          ].flatten
+        end
+
+        it 'returns the sum of the penalties for each pair of guests' do
+          expect(calculator.send(:cohesion_penalty)).to eq(4 * 1 + 4 * Rational(1, 2) + 4 * Rational(2, 3))
+        end
+      end
+
+      context 'when the table contains six guests of three unevenly split groups' do
+        let(:table) do
+          [
+            create_list(:guest, 3, affinity_group_list: ['family']),
+            create_list(:guest, 2, affinity_group_list: ['friends']),
+            create_list(:guest, 1, affinity_group_list: ['work'])
+          ].flatten
+        end
+
+        it 'returns the sum of the penalties for each pair of guests' do
+          expect(calculator.send(:cohesion_penalty)).to eq(6 * 1 + 2 * Rational(1, 2) + 3 * Rational(2, 3))
+        end
+      end
+    end
+  end
+end