Module: Equalshares::Comparison

Defined in:
lib/equalshares/comparison.rb

Overview

Comparison step. Faithful port of comparisonStep() in js/methodOfEqualSharesWorker.js. Compares the MES committee against the greedy committee; if a strict majority of voters prefer greedy, the outcome switches.

Class Method Summary collapse

Class Method Details

.comparison_step(voter_ids, approvers, greedy, winners, params) ⇒ Object 



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# File 'lib/equalshares/comparison.rb', line 10

def comparison_step(voter_ids, approvers, greedy, winners, params)
  prefers_mes = 0
  prefers_greedy = 0

  case params.comparison
  when "satisfaction"
    mes_satisfaction = Hash.new(0)
    greedy_satisfaction = Hash.new(0)
    [[winners, mes_satisfaction], [greedy, greedy_satisfaction]].each do |candidates, satisfaction|
      candidates.each do |c|
        approvers[c].each { |i| satisfaction[i] += 1 }
      end
    end
    voter_ids.each do |i|
      if mes_satisfaction[i] > greedy_satisfaction[i]
        prefers_mes += 1
      elsif greedy_satisfaction[i] > mes_satisfaction[i]
        prefers_greedy += 1
      end
    end
  when "exclusionRatio"
    mes_approvals = {}
    winners.each { |c| approvers[c].each { |i| mes_approvals[i] = true } }
    greedy_approvals = {}
    greedy.each { |c| approvers[c].each { |i| greedy_approvals[i] = true } }
    voter_ids.each do |i|
      if mes_approvals[i] && !greedy_approvals[i]
        prefers_mes += 1
      elsif greedy_approvals[i] && !mes_approvals[i]
        prefers_greedy += 1
      end
    end
  end

  stick_to_mes = prefers_greedy <= prefers_mes
  { stick_to_mes: stick_to_mes, prefers_mes: prefers_mes, prefers_greedy: prefers_greedy }
end