Module: Equalshares::Tie

Defined in:
lib/equalshares/tie_breaking.rb

Overview

Tie-breaking facade. Composes the TieBreaker strategies named in params.tie_breaking to either resolve a single tie (break_ties) or build a total order (total_order).

Class Method Summary collapse

Class Method Details

.break_ties(_project_ids, cost, approvers, params, choices) ⇒ Object

Resolve a tie among choices by applying each tie-breaking strategy in priority order, narrowing the set. Returns the surviving candidates (callers treat more than one as an unresolved tie).

Raises:



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# File 'lib/equalshares/tie_breaking.rb', line 12

def break_ties(_project_ids, cost, approvers, params, choices)
  ctx = TieBreaker::Context.new(cost, approvers)
  remaining = params.tie_breaking.reduce(choices.dup) do |current, method|
    TieBreaker.for(method).filter(current, ctx)
  end

  raise ComputeError, "Tie-breaking failed in a way that should not happen: #{choices}" if remaining.empty?

  remaining
end

.resolve_one(project_ids, cost, approvers, params, choices) ⇒ Object

Resolve a tie down to a single winner, raising if the tie-breaking rules leave more than one candidate. Used by the sequential rules.



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# File 'lib/equalshares/tie_breaking.rb', line 25

def resolve_one(project_ids, cost, approvers, params, choices)
  resolved = break_ties(project_ids, cost, approvers, params, choices)
  if resolved.length > 1
    raise ComputeError,
          "Tie-breaking failed: tie between projects #{resolved.join(', ')} could not be resolved. " \
          "Another tie-breaking needs to be added."
  end
  resolved[0]
end

.total_order(project_ids, cost, approvers, params) ⇒ Object

A total order of all projects induced by params.tie_breaking, used by rules that need a full ordering (e.g. greedy welfare). Projects are sorted by each strategy's sort key in priority order, falling back to their original (JS Object.keys) order.



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# File 'lib/equalshares/tie_breaking.rb', line 38

def total_order(project_ids, cost, approvers, params)
  ctx = TieBreaker::Context.new(cost, approvers)
  strategies = params.tie_breaking.map { |method| TieBreaker.for(method) }
  base_index = project_ids.each_with_index.to_h

  project_ids.sort_by do |c|
    strategies.map { |strategy| strategy.sort_key(c, ctx) } + [base_index[c]]
  end
end