# -*- coding: utf-8 -*-
"""
Copyright Sylvain Bouveret, Yann Chevaleyre and François 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.rules.rule_score_num import RuleScoreNum
from whalrus.scorers.scorer import Scorer
from whalrus.utils.utils import cached_property, NiceDict, my_division
from numbers import Number
[docs]class RuleScoreNumAverage(RuleScoreNum):
"""
A voting rule where each candidate's score is an average of the scores provided by the ballots.
Parameters
----------
args
Cf. parent class.
scorer : Scorer
For each ballot, it is in charge of computing its contribution to each candidate's score.
default_average : Number
The default average score of a candidate when it receives no score whatsoever. It may happen, for example, if
all voters abstain about this candidate. This avoids a division by zero when computing this candidate's average
score.
kwargs
Cf. parent class.
Examples
--------
Cf. :class:`RuleRangeVoting` for some examples.
"""
def __init__(self, *args, scorer: Scorer = None, default_average: Number = 0, **kwargs):
self.scorer = scorer
self.default_average = default_average
super().__init__(*args, **kwargs)
@cached_property
def _gross_scores_and_weights_(self) -> dict:
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
return {'gross_scores': gross_scores, 'weights': weights}
@cached_property
def gross_scores_(self) -> NiceDict:
"""NiceDict: The gross scores of the candidates. For each candidate, this dictionary gives the sum of its
scores, multiplied by the weights of the corresponding voters. This is the numerator in the candidate's average
score.
"""
return self._gross_scores_and_weights_['gross_scores']
@cached_property
def weights_(self) -> NiceDict:
"""NiceDict: The weights used for the candidates. For each candidate, this dictionary gives the total weight
for this candidate, i.e. the total weight of all voters who assign a score to this candidate. This is the
denominator in the candidate's average score.
"""
return self._gross_scores_and_weights_['weights']
@cached_property
def scores_(self) -> NiceDict:
return NiceDict({c: my_division(score, self.weights_[c], divide_by_zero=self.default_average)
for c, score in self.gross_scores_.items()})
# Conversion to floats
# --------------------
@cached_property
def gross_scores_as_floats_(self) -> NiceDict:
"""NiceDict: Gross scores as floats. It is the same as :attr:`gross_scores_`, but converted to floats.
"""
return NiceDict({c: float(v) for c, v in self.gross_scores_.items()})
@cached_property
def weights_as_floats_(self) -> NiceDict:
"""NiceDict: Weights as floats. It is the same as :attr:`weights_`, but converted to floats.
"""
return NiceDict({c: float(v) for c, v in self.weights_.items()})