Source code for whalrus.rules.rule_bucklin_by_rounds

# -*- coding: utf-8 -*-
"""
Copyright Sylvain Bouveret, Yann Chevaleyre and Fran├žois Durand
sylvain.bouveret@imag.fr, yann.chevaleyre@dauphine.fr, fradurand@gmail.com

This file is part of Whalrus.

Whalrus is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

Whalrus is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with Whalrus.  If not, see <http://www.gnu.org/licenses/>.
"""
from whalrus.scorers.scorer_bucklin import ScorerBucklin
from whalrus.rules.rule_score_num import RuleScoreNum
from whalrus.converters_ballot.converter_ballot_to_order import ConverterBallotToOrder
from whalrus.utils.utils import cached_property, NiceDict, my_division
from whalrus.converters_ballot.converter_ballot import ConverterBallot
from fractions import Fraction


[docs]class RuleBucklinByRounds(RuleScoreNum): """ Bucklin's rule (round by round version). During the first round, a candidate's score is the proportion of voters who rank it first. During the second round, its score is the proportion of voters who rank it first or second. Etc. More precisely, at each round, the ``scorer`` is used with ``k`` equal to the round number; cf. :class:`ScorerBucklin`. For another variant of Bucklin's rule, cf. :class:`RuleBucklinInstant`. Parameters ---------- args Cf. parent class. converter : ConverterBallot Default: :class:`ConverterBallotToOrder`. scorer : Scorer Default: :class:`ScorerBucklin`. kwargs Cf. parent class. Examples -------- >>> rule = RuleBucklinByRounds(['a > b > c > d', 'b > a > c > d', ... 'c > a > b > d', 'd > a > b > c']) >>> rule.detailed_scores_[0] {'a': Fraction(1, 4), 'b': Fraction(1, 4), 'c': Fraction(1, 4), 'd': Fraction(1, 4)} >>> rule.detailed_scores_[1] {'a': 1, 'b': Fraction(1, 2), 'c': Fraction(1, 4), 'd': Fraction(1, 4)} >>> rule.n_rounds_ 2 >>> rule.scores_ {'a': 1, 'b': Fraction(1, 2), 'c': Fraction(1, 4), 'd': Fraction(1, 4)} >>> rule.winner_ 'a' """ def __init__(self, *args, converter: ConverterBallot = None, scorer: ScorerBucklin = None, **kwargs): # Default value if converter is None: converter = ConverterBallotToOrder() if scorer is None: scorer = ScorerBucklin() # Parameters self.scorer = scorer super().__init__(*args, converter=converter, **kwargs) @cached_property def detailed_scores_(self) -> list: """list: Detailed scores. A list of :class:`NiceDict`. The first dictionary gives the scores of the first round, etc. """ n_candidates = len(self.candidates_) detailed_scores = [] for k in range(1, n_candidates + 1): self.scorer.k = k gross_scores = NiceDict({c: 0 for c in self.candidates_}) weights = NiceDict({c: 0 for c in self.candidates_}) for ballot, weight, voter in self.profile_converted_.items(): for c, value in self.scorer(ballot=ballot, voter=voter, candidates=self.candidates_).scores_.items(): gross_scores[c] += weight * value weights[c] += weight scores = NiceDict({c: my_division(score, weights[c], divide_by_zero=0) for c, score in gross_scores.items()}) detailed_scores.append(scores) if max(scores.values()) > Fraction(1, 2): break return detailed_scores @cached_property def scores_(self) -> NiceDict: """NiceDict: The scores. For each candidate, it gives its score during the final round, i.e. the first round where at least one candidate has a score above 1 / 2. """ return self.detailed_scores_[-1] @cached_property def n_rounds_(self) -> int: """int: The number of rounds. """ return len(self.detailed_scores_) # Conversion to floats # -------------------- @cached_property def detailed_scores_as_floats_(self) -> list: """list: Detailed scores, as floats. It is the same as :attr:`detailed_scores_`, but converted to floats. Examples -------- >>> rule = RuleBucklinByRounds(['a > b > c > d', 'b > a > c > d', ... 'c > a > b > d', 'd > a > b > c']) >>> rule.detailed_scores_as_floats_[0] {'a': 0.25, 'b': 0.25, 'c': 0.25, 'd': 0.25} >>> rule.detailed_scores_as_floats_[1] {'a': 1.0, 'b': 0.5, 'c': 0.25, 'd': 0.25} """ return [NiceDict({c: float(v) for c, v in counting_round.items()}) for counting_round in self.detailed_scores_]