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CHANGELOG.md

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Changelog

All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog, and this project adheres to Semantic Versioning.

Unreleased

[3.0.0] - 2024-08-15

Added

  • The election methods thanks to @kevin-q2. The newest election methods are PluralityVeto, RandomDictator, and BoostedRandomDictator.
  • More comprehensive tests for the Ballot class.
  • More comprehensive tests for all of the election types.
  • More comprehensive tests for the PreferenceProfile class.
  • Tests for potential errors in the BallotGenerator classes.

Changed

  • Moved the following election methods to sorted folders in src/votekit/elections/election_types:

    • approval
      • Approval
      • BlockPlurality
    • ranking
      • RankingElection
      • Alaska
      • BoostedRandomDictator
      • Borda
      • CondoBorda
      • DominatingSets
      • PluralityVeto
      • Plurality
      • SNTV
      • RandomDictator
    • scores
      • GeneralRating
      • Limited
      • Rating
      • Cumulative

  • Updated / added the following methods to src/votekit/utils.py:

    • ballots_by_first_cand
    • remove_cand
    • add_missing_cands
    • validate_score_vector
    • score_profile
    • first_place_votes
    • mentions
    • borda_scores
    • tie_broken_ranking
    • score_dict_to_ranking
    • elect_cands_from_set_ranking
    • expand_tied_ballot
    • resolve_profile_ties

  • Changed the way that the ElectionState class operates. It now operates as a dataclass storing the following data:

    • round_number: The round number of the election.
    • remaining: The remaining candidates in the election that have not been elected.
    • elected: The set of candidates that have been elected.
    • eliminated: The set of candidates that have been eliminated.
    • tiebreak_winners: The set of candidates that were elected due to a tiebreak within a round.
    • scores: The scores for each candidate in the election.

  • The PreferenceProfile class is now a frozen dataclass with the idea being that, once the ballots and candidates for an election have been set, they should not be changed.

    • Several validators have also been added to the PreferenceProfile class to ensure that the ballots and candidates are valid.

  • Updated all documentation to reflect major changes in the API of the package.

Fixed

[2.0.1] - 2024-06-11

Added

  • Created a read the docs page.
  • Add scale parameter to ballot_graph.draw() to allow for easier reading of text labels.
  • Allow users to choose which bloc is W/C in historical Cambridge data for CambridgeSampler.

Changed

  • Updated tutorial notebooks; larger focus on slate models, updated notebooks to match current codebase.
  • Removed the seq-RCV transfer rule since it is a dummy function, replaced with lambda function.
  • Update plot MDS to have aspect ratio 1, remove axes labels since they are meaningless in MDS.
  • Update all BLT files in scot-elex repo to be true CSV files, updated load_scottish accordingly.

Fixed

  • Fixed bug by which slate-PlackettLuce could not generate ballots when some candidate had 0 support.
  • Updated various functions in the ballot generator module to only generate ballots for non-zero candidates.
  • Fixed one bloc s-BT pdf, which was incorrectly giving 0 weight to all ballot types.

[2.0.0] - 2024-03-04

Added

  • A PreferenceInterval class.

  • MCMC sampling for both BradleyTerry ballot generators.

  • Add print statement to BallotGraph so that when you draw the graph without labels, it prints a dictionary of candidate labels for you.

  • Add an IRV election class, which is just a wrapper for STV with 1 seat.

  • Add default option to Borda election class, so users do not have to input a score vector if they want to use the traditional Borda vector.

  • Add several methods to PairwiseComparisonGraph. Added two boolean methods that return True if there is a condorcet winner or if there is a condorcet cycle. Added two get methods that return the winner or the cycles. Cached the results of dominating_tiers and get_condorcet_cycles.

  • Added optional to_float method to first_place_votes if users want to see them as floats instead of Fractions.

  • Added a by_bloc parameter to generate_profile. If True, this returns a tuple, the first entry of which is a dictionary of PreferenceProfiles by bloc. The second entry is the aggregated profile. This is very helpful for analyzing the behavior of a single bloc of voters. Defaults to False for backwards compatibility.

  • Created a Cumulative ballot generator class. The Cumulative class works like PL, but samples with replacement instead of without. The ranking order does not matter here, simply that candidates are listed on the ballot with multiplicity.

  • Created a HighestScore election class. This takes in a profile and a score vector, and returns the candidates with highest scores. There is a lot of flexibility in the score vector, so this class can run things like Borda, cumulative, etc.

  • Created a Cumulative election class which is just a subclass of HighestScore with the score vector set to all 1s. Thus anyone appearing on the ballot gets one point for each time they appear.

  • Wrote an __add__ method for PreferenceProfile that combines the ballot lists of two profiles.

  • Created utility functions to compute the winners of a profile given a score vector, as well as to validate a score vector (non-negative and non-increasing).

  • Created a shortPlackettLuce class which allows you to generate ballots of arbitrary length in the style of PL.

  • Added tests for __add__ method of PreferenceProfile.

  • Added SlatePreference model and tests.

Changed

  • Change the way the condense_ballots() method works in profiles. Rather than altering the original profile, it returns a new profile. This gives users the option to preserve the original profile.

  • Alter STV class so that the remaining candidates are always listed in order of current first place votes.

  • Made PlackettLuce a subclass of shortPlackettLuce.

  • Change PlackettLuce, BradleyTerry, and Cumulative ballot generators to have name_ prefix. This is in contrast to the slate_ models we have introduced.

  • Speed improvements for various ballot generators.

  • pref_interval_by_bloc is now pref_intervals_by_bloc in all ballot generators. This is now a dictionary of dictionaries, where the both sets of keys are the blocs, and the values of the sub-dictionaries are PreferenceInterval objects. The slate models require that we sample from the uncombined PreferenceInterval objects, while the name models require that we combine the PreferenceInterval objects using cohesion parameters.

  • MDS plot functionality, splitting it into compute_MDS which computes the coordinates, and plot_MDS which plots them. Made because the computation is the most time intensive.

Fixed

  • Fixed an error in the PreferenceProfile tail method.

  • Errors in bloc labeling in CambridgeSampler.

1.1.0 - 2023-11-28

Added

  • Added to_dict(), to_json() functions for ElectionState (107).
  • Scores attribute to ElectionState (113).
  • Post init to Ballots, handles conversion from float/int types to Fraction (113).
  • _rename_blocs method to CambridgeSampler to rename blocs to historical names.
  • Added reset and run_to_step methods to Election class (116).
  • sort_by_weight parameter to head and tail methods of PreferenceProfile (115).
  • received_votes parameter to get_candidates method of PreferenceProfile. If True, only return candidates that received votes (115).
  • __str__ method for Ballot (114).
  • Social choice theory documentation (112).

Changed

  • Method names for ElectionState methods (107).
  • Caches for the results of run_election() (107).
  • Optimized random_transfer function (113).
  • Ballot objects made immutable, using Pydantic dataclass (113).
  • PrefrenceProfile's get_ballots() returns a copy of the ballots list (113).
  • compute_votes() returns dictionary and list of tuple to avoid recomputing values (113).
  • Parameter names for CambridgeSampler.
  • Where the edge labels for PairwiseComparisonGraph print, from 1/2 to 1/3.
  • The BallotGraph now always displays vote totals for a ballot (116).
  • ElectionState now prints the current round whenever printing (116).
  • load_blt became load_scottish (116).
  • plot_summary_stats always displays candidates in order inputted (115).
  • PreferenceProfile data frame now has Percent column, removed the Weight Share column (115).
  • Ballot object can take floats and ints as weights (114).
  • Ballot attribute voter changed to voter_set (114).

Fixed

  • Multiple winners correctly ordered based off previous rounds vote totals (113)
  • CambridgeSampler correctly computes the frequency of opposing bloc ballots.
  • PreferenceProfile no longer rounds all weights to integer when printing (114).

1.0.2 - 2023-09-09

Fixed

  • Bug fixes for election state

Changed

  • Lowered pandas version requirements for wider compatibility

1.0.1 - 2023-09-03

Added

  • Elections submodule (e.g from votekit.elections import STV, fractional_transfer)
  • More documentation for ballot generators

Changed

  • Renamed CVR loaders to load_csv and load_blt

1.0.0 - 2023-09-01

Added

  • User determined options for breaking ties
  • Ballot Simplex object, refactored construction for ballot generator classes
  • IC/IAC with generalized arguments
  • Improved handling of tied rankings within ballots

Fixed

  • Allow imports from the module level

Changed

  • Optimization for election helper functions