# Does STV according to
# http://www.rosenstiel.co.uk/stvrules/av/index.htm
+# Usage:
+# ./stv [TIEBREAK ...] PLACES [INPUT-FILES ...]
+#
+# PLACES is the number of seats to be filled
+#
+# INPUT-FILES are in the format:
+# VOTER PQRST
+# where P, Q, R, etc. are candidates. Candidates
+# must be single letters.
+#
+# Each TIEBREAK is
+# P,Q,...
+
use strict;
use utf8;
use autodie;
use bigrat;
+use Carp;
+use Data::Dumper;
+use List::Util qw(sum0);
+use List::MoreUtils qw(nsort_by);
# vote is
# { Voter => opaque,
our $stage=0;
our @allvotes;
+our %tiebreak; # $tiebreak{ winningcand }{ losingcand } = 1
+
+while (@ARGV && $ARGV[0] =~ m/[<>]/) {
+ my ($losers, $winners) = ($? eq '<' ? ($`, $') : ($', $`));
+ my @losers = sort split /\,/, $losers;
+ my @winners = sort split /\,/, $winners;
+ die "@losers @winners" if @losers>1 && @winners>1;
+ my @all = sort @losers, @winners;
+ my $record = sub {
+ my ($how, $howers) = @_;
+ return unless @$howers == 1;
+ die "@all $how" if defined $tiebreak{$how}{"@all"};
+ $tiebreak{$how}{"@all"} = $howers->[0];
+ };
+ $record->('winner', \@winners);
+ $record->('loser', \@losers);
+ shift @ARGV;
+}
+
our $places = shift @ARGV;
die unless $places eq ($places + 0);
+open DEBUG, ">.stv.log" or die $!;
+
while (<>) {
- m/^(\w+) ([A-Z]+)$/ or die;
- my $prefs = $1;
+ next if m/^\w+$/;
+ m/^(\w+) ([A-Z]+)$/ or die "$_ ?";
+ my $prefs = $2;
my $vote = {
Voter => $1,
Weight => 1.0,
- Prefs => (split //, $prefs),
+ Prefs => [ split //, $prefs ],
};
push @allvotes, $vote;
}
sub pr ($) {
my ($f) = @_;
- return sprintf "%10.6f=%-10s", $f, $f;
+ confess unless defined $f;
+ return sprintf "%10.6f = %-10s", $f, $f;
}
sub votelog ($$) {
push @{ $vote->{Log} }, "stage $stage: $m";
}
-sub filterout ($$) {
- my ($cand, $why) = @_;
- foreach my $vote (@allvotes) {
- my $oldprefs = $vote->{Prefs};
- my @prefs = grep { $_ ne $cand } $oldprefs;
- next if @prefs == @$oldprefs;
- votelog $vote, "crossed out candidate $cand: $why";
+our @elected; # $elected[] = $candidate
+
+our @unsorted = @allvotes;
+
+our %sorted;
+# $sorted{$firstpref}{Votes} = [ $vote, ... ]
+# $sorted{$firstpref}{Cand} = $firstpref
+# $sorted{$firstpref}{Total} = $totalweight
+our @surpluses; # values same as %sorted
+
+our @exhausted; # votes
+
+our %continuing; # $continuing{$candidate}=1
+
+our @stagerecord; # $stagerecord[]{$candidate} = $total
+
+sub voteliveprefs ($) {
+ my ($vote) = @_;
+ grep { $continuing{$_} } @{ $vote->{Prefs} };
+}
+
+sub votelogfull ($$) {
+ my ($vote,$m) = @_;
+ votelog $vote, $m;
+ votelog $vote, ("continuing prefs: ". join ' ', voteliveprefs $vote);
+}
+
+foreach my $vote (@allvotes) {
+ $continuing{$_}=1 foreach @{ $vote->{Prefs} };
+}
+
+sub equalpiles ($@) {
+ my ($how, @sorted) = @_;
+ return () unless @sorted;
+ my $s = $sorted[0];
+ my $eqtotal = $s->{Total};
+ my $count = 0/1;
+ while ($count < @sorted && $sorted[$count]{Total} == $eqtotal) {
+ printf "%7s %10s %s\n", $how, $sorted[$count]{Cand},
+ pr $sorted[$count]{Total};
+ $count++;
}
+ return @sorted[ 0 .. $count-1 ];
+}
+
+sub historically_prefer ($@) {
+ my ($signum, @choices) = @_;
+ # $signum==+1 means choose candidates with more early preferences
+
+ return $choices[0] if @choices < 2;
+
+ my $compare = sub {
+ foreach my $sr (@stagerecord) {
+ my $d = ($sr->{ $a->{Cand} }//0) <=> ($sr->{ $b->{Cand} }//0);
+ return -$d * $signum if $d;
+ }
+ return 0;
+ };
+
+ @choices = sort $compare @choices;
+
+ print DEBUG "historically_prefer\n",
+ Data::Dumper->Dump([\@choices, \@stagerecord],
+ [qw(_@choices _@stagerecord)]);
+
+ foreach my $s (@choices) {
+ my $c = $s->{Cand};
+ printf " %6s %10s |", 'tiebrk', $c;
+ foreach my $sr (@stagerecord) {
+ my $p = pr($sr->{$c} // 0);
+ $p =~ s/\.0+\b//g;
+ $p =~ s/ //g;
+ print "$p|";
+ }
+ print "\n";
+ }
+
+ $a = $choices[0];
+ my $numequal = 1;
+ for (;;) {
+ last if $numequal >= @choices;
+ $b = $choices[$numequal];
+ last if $compare->();
+ $numequal++;
+ }
+
+ if ($numequal > 1) {
+ my $how = $signum > 0 ? 'winner' : 'loser';
+ my @all = sort map { $_->{Cand} } @choices[ 0 .. $numequal-1 ];
+ my $hower = $tiebreak{$how}{"@all"};
+ if (defined $hower) {
+ printf "%7.7s %10s !!!!!!!!!!\n", "TIE".(uc $how), $hower;
+ return grep { $_->{Cand} eq $hower } @choices;
+ }
+ die "need tie break for $how between @all\n";
+ }
+
+ return $choices[0];
+}
+
+foreach my $c (keys %continuing) {
+ $sorted{$c} = {
+ Cand => $c,
+ Votes => [],
+ };
}
for (;;) {
$stage++;
- my %sorted;
- # $sorted{firstpref}{Votes} = [ $vote, ... ]
- # $sorted{firstpref}{Total} = [ $vote, ... ]
- for my $vote (@allvotes) {
- next unless @{ $vote->{Prefs} };
- my $firstpref = $vote->{Prefs}[0];
- push @{ $sorted{$firstpref}{Votes} }, $vote;
+ printf "----- stage %d -----\n", $stage;
+
+ print DEBUG "#################### $stage ####################\n",
+ Data::Dumper->Dump(
+[ \@stagerecord, \@elected, \@unsorted, \%sorted, \@surpluses, \%continuing ],
+[qw( _@stagerecord _@elected _@unsorted _%sorted _@surpluses _%continuing )]
+ );
+
+ my $placesremain = $places - @elected;
+
+ unless ($placesremain > 0) {
+ printf "Complete: @elected\n";
+ last;
+ }
+
+ while (my $vote = shift @unsorted) {
+ my ($firstpref) = voteliveprefs $vote;
+ if (!defined $firstpref) {
+ votelog $vote, "ballot exhausted";
+ push @exhausted, $vote;
+ } else {
+ push @{ $sorted{$firstpref}{Votes} }, $vote;
+ }
}
foreach my $firstpref (sort keys %sorted) {
foreach my $vote (@{ $sorted{$firstpref}{Votes} }) {
- votelog $vote, "counted $vote->{Weight] for $firstpref";
- $sorted{$firstpref}{Total} += $vote->{Weight};
+ votelog $vote, "counted for $firstpref ".pr $vote->{Weight};
}
}
- my @sorted = sort {
- $sorted{$b}{Total} <=> $sorted{$a}{Total};
- } keys %sorted;
-
- my $totalvalid = 0;
- foreach my $firstpref (@sorted) {
- $sorted{$firstpref}{Total} += $_->{Weight}
- foreach @{ $sorted{$firstpref}{Votes} };
- printf "%10s %s\n", $firstpref, pr $sorted{$firstpref}{Total};
- $totalvalid += $sorted{$firstpref}{Total};
+ my @sorted;
+ my $things_update = sub {
+ foreach my $s (values %sorted) {
+ $s->{Total} = sum0 map { $_->{Weight} } @{ $s->{Votes } };
+ }
+ @sorted = nsort_by { -$_->{Total} } values %sorted;
+ };
+ $things_update->();
+
+ print DEBUG "SORTED\n", Dumper(\@sorted);
+
+ push @stagerecord, { map { ($_->{Cand}, $_->{Total}) } @sorted };
+
+ my $totalvalid = 0/1;
+ my $countvalid = sub {
+ my ($l, $what) = @_;
+ foreach my $s (@$l) {
+ printf "%-7s %10s %s\n", $what, $s->{Cand}, pr $s->{Total};
+ $totalvalid += $s->{Total};
+ }
+ };
+ $countvalid->(\@sorted, '1stpref');
+ $countvalid->(\@surpluses, 'surplus');
+
+ printf "%7s %10s %s\n", 'TOTAL', '-----', pr $totalvalid;
+
+ unless ($totalvalid > 0) {
+ printf "No more votes!\n";
+ last;
}
- printf "%10s %s\n", 'TOTAL', pr $totalvalid;
- last unless $totalvalid > 0;
+ my $quota = $totalvalid / ($placesremain + 1);
+ printf "%7s %10s %s\n", 'quota', '', pr $quota;
+
+ my $need_to_transfer_surplus = 1;
- my $quota = $totalvalid / ($places + 1);
- printf "\nquota = %10s\n", pr $quota;
+ my @newsurpluses;
- my $topfirst = $sorted[0];
- my $topvoters = $sorted{ }{Weight};
- my $surplus = $topvoters - $quota;
- if ($surplus >= 0) {
- printf "%10s ELECTED\n", $sorted[0];
+ # Look for people to elect.
+ # We elect as many as we can, rather than recomputing the (lower) quota
+ # (ERS rules 5.4.9)
+ for (;;) {
+ my $s = $sorted[0];
+ my $topvoters = $s->{Total};
+ my $surplus = $topvoters - $quota;
+ last unless $surplus >= 0;
+ last unless $placesremain;
- # transfer the surplus
- my $weightmult = $surplus / $topvoters;
- foreach my $vote (@{ $sorted{$topfirst}{Votes} }) {
- votelog $vote, "part of surplus of weight $weightmult";
- $vote->{Weight} *= $weightmult;
+ my @elect = equalpiles 'elect?', @sorted;
+
+ if (@elect > $placesremain) {
+ # oh my god
+ @elect = historically_prefer +1, @elect;
+ printf "%7s %10s\n", 'tie!', $elect[0]{Cand};
+ }
+
+ foreach $s (@elect) {
+ printf "%7s %10s ***************\n", 'ELECTED', $s->{Cand};
+ push @elected, $s->{Cand};
+
+ foreach my $vote (@{ $s->{Votes} }) {
+ votelog $vote, "elected $s->{Cand}";
+ }
+
+ $s->{Surplus} = $surplus;
+ push @newsurpluses, $s;
+ delete $sorted{ $s->{Cand} };
+ delete $continuing{ $s->{Cand} };
+ $placesremain--;
}
- filterout $topfirst, "candidate was elected";
- } else {
- my $elim = $sorted{ $#sorted };
- printf "%10s eliminated\n", $elim;
- filterout $elim, "candidate was eliminated";
+
+ $things_update->();
}
+
+ foreach my $s (@newsurpluses) {
+ # calculate the transfer value of each surplus
+ # we do this simultaneously, but based on the number of
+ # continuing candidates (excluding all the ones elected already)
+ # ERS rule 5.3.3
+
+ my $votes = $s->{Votes};
+ my $surplus = $s->{Surplus};
+ my $transferrable =
+ sum0
+ map { $_->{Weight} }
+ grep { !!voteliveprefs $_ }
+ @$votes;
+
+ my $derate = 1/1;
+ printf "%7s %10s %s\n", 'xfrable', $s->{Cand}, pr $transferrable;
+ if ($transferrable > $surplus) {
+ $derate = $transferrable / $surplus;
+ printf "%7s %10s %s\n", 'derate', $s->{Cand}, pr $derate;
+ foreach my $vote (@{ $s->{Votes} }) {
+ votelog $vote, "part of surplus, derated ". pr $derate;
+ $vote->{Weight} /= $derate;
+ }
+ }
+ $s->{Total} = $transferrable / $derate;
+
+ push @surpluses, $s;
+
+ $things_update->();
+ printf "%7s %10s %s\n", 'surplus', $s->{Cand}, pr $s->{Total};
+
+ $need_to_transfer_surplus = 0;
+ # before actually transferring a surplus, we will consider
+ # eliminating, and then reconsider with a lower quota
+ }
+
+ my $deferredsurplus = sum0 map { $_->{Total} } @surpluses;
+ printf "%18s %s\n", 'deferred surplus', pr $deferredsurplus;
+
+ # Look for people to eliminate
+ # We eliminate before trying to transfer surpluses
+ # ERS 5.2.5
+ my $elimvotebefore = 0/1;
+ for (;;) {
+ last unless @sorted;
+
+ if ($elimvotebefore) {
+ printf "%18s %s\n", 'elimination, sofar', pr $elimvotebefore;
+ } elsif (@surpluses) {
+ printf "%18s\n", 'elimination, maybe';
+ } else {
+ printf "%18s\n", 'elimination, starts';
+ }
+
+ my @elim = equalpiles 'elim?', reverse @sorted;
+ my $elimvotenow = sum0 map { $_->{Total} } @elim;
+
+ if (@surpluses || $elimvotebefore) {
+ # rule 5.2.2
+ if (@sorted == @elim) {
+ printf "%18s\n", 'no-elim (all-equal)';
+ last;
+ }
+ my $nextup = $sorted[ $#sorted - @elim ];
+ printf "%7s %10s %s\n", 'nextup', $nextup->{Cand},
+ pr $nextup->{Total};
+ my $aheadby = $nextup->{Total} - ($elimvotenow + $elimvotebefore);
+ unless ($deferredsurplus <= $aheadby) {
+ # rule 5.2.2 (b)
+ printf "%18s %s\n", 'no-elim (nextup)', pr $aheadby;
+ last;
+ }
+ }
+
+ my $elim_tie =
+ @elim > 1 &&
+ (scalar keys %continuing) - (scalar @elim) < $placesremain;
+ if ($elim_tie) {
+ # eliminate only one then, and try again
+ printf "elim-tie!\n";
+ @elim = historically_prefer -1, @elim;
+ }
+
+ foreach my $s (@elim) {
+ my $c = $s->{Cand};
+ printf "%7s %10s %s\n", 'ELIM', $c, '----------';
+ my $votes = $s->{Votes};
+ votelogfull $_, "failed to stop $c elimination" foreach @$votes;
+ $elimvotebefore += $s->{Total};
+ delete $continuing{$c};
+ delete $sorted{$c};
+ push @unsorted, @$votes;
+ }
+
+ $things_update->();
+ $need_to_transfer_surplus = 0;
+ last if $elim_tie; # no more, then!
+ }
+
+ next unless $need_to_transfer_surplus;
+
+ @surpluses = nsort_by { $_->{Total} } @surpluses;
+ my @surplusxfer = equalpiles 'xfer?', @surpluses;
+ die unless @surplusxfer;
+
+ if (@surplusxfer > 1) {
+ @surplusxfer = historically_prefer +1, @surplusxfer;
+ }
+
+ my $s = $surplusxfer[0];
+ my $c = $s->{Cand};
+ printf "%7s %10s\n", 'xfer', $c;
+ my $votes = $s->{Votes};
+ votelogfull $_, "surplus transferred" foreach @$votes;
+ @surpluses = grep { $_->{Cand} ne $c } @surpluses;
+ push @unsorted, @$votes;
}
+
+open VL, ">.stv.votes" or die $!;
+foreach my $vote (@allvotes) {
+ print VL "----------------------------------------\n";
+ print VL "voter $vote->{Voter}\n";
+ print VL "prefs ". (join " ", @{ $vote->{Prefs} }). "\n";
+ print VL $_, "\n" foreach @{ $vote->{Log} };
+}
+print VL "========================================\n";
+close VL;
+
+print "done.\n";
~ian / appendix-a6.git / blobdiff