ScorerPositional

class whalrus.ScorerPositional(*args, points_scheme: list = None, points_fill: Optional[numbers.Number] = 0, points_unordered: Optional[numbers.Number] = 0, points_absent: Optional[numbers.Number] = None, **kwargs)

A positional scorer for strict order ballots.

Parameters

• args – Cf. parent class.

• points_scheme (list) – The list of points to be attributed to the (first) candidates of a ballot.

• points_fill (Number or None) – Points for ordered candidates that have a rank beyond the points_scheme.

• points_unordered (Number or None) – Points for the unordered candidates.

• points_absent (Number or None) – Points for the absent candidates.

• kwargs – Cf. parent class.

Examples

The top candidate in the ballot receives points_scheme[0] points, the second one receives points_scheme[1] points, etc:

>>> ScorerPositional(ballot=BallotOrder('a > b > c'), points_scheme=[10, 5, 3]).scores_
{'a': 10, 'b': 5, 'c': 3}

The points scheme does not need to have the same length as the ballot:

>>> ScorerPositional(ballot=BallotOrder('a > b > c'), points_scheme=[3, 2, 1, .5]).scores_
{'a': 3, 'b': 2, 'c': 1}
>>> ScorerPositional(ballot=BallotOrder('a > b > c'), points_scheme=[3, 2]).scores_
{'a': 3, 'b': 2, 'c': 0}

A typical usage of this is k-Approval voting:

>>> ScorerPositional(ballot=BallotOrder('a > b > c > d > e'), points_scheme=[1, 1]).scores_
{'a': 1, 'b': 1, 'c': 0, 'd': 0, 'e': 0}

In the example below, candidates a, b and c are “ordered”, d is “unordered”, and e is “absent” in the ballot, meaning that e was not even available when the voter cast her ballot. The options of the scorer provide different ways to take these special cases into account:

>>> ballot=BallotOrder('a > b > c', candidates={'a', 'b', 'c', 'd'})
>>> candidates_election = {'a', 'b', 'c', 'd', 'e'}
>>> ScorerPositional(ballot, candidates=candidates_election, points_scheme=[3, 2]).scores_
{'a': 3, 'b': 2, 'c': 0, 'd': 0}
>>> ScorerPositional(ballot, candidates=candidates_election, points_scheme=[3, 2],
...     points_fill=-1, points_unordered=-2, points_absent=-3).scores_
{'a': 3, 'b': 2, 'c': -1, 'd': -2, 'e': -3}
>>> ScorerPositional(ballot, candidates=candidates_election, points_scheme=[3, 2],
...     points_fill=None, points_unordered=None, points_absent=None).scores_
{'a': 3, 'b': 2}

property scores_as_floats_

The scores, given as floats. It is the same as scores_, but converted to floats.

Like all conversions to floats, it is advised to use this attribute for display purposes only. For computation, you should always use scores_, which usually manipulates fractions and therefore allows for exact computation.

Raises

ValueError – If the scores cannot be converted to floats.

Type

NiceDict