private int[,] GetPairwisePreferences(VoteStorage taskVotes)
{
int[,] pairwisePreferences = new int[taskVotes.Count, taskVotes.Count];
var choiceIndexes = GetChoicesIndexes(taskVotes.Keys);
// Invert the votes so that we can look at preferences per user.
var voterPreferences = taskVotes.SelectMany(v => v.Value).GroupBy(u => u.Key).ToDictionary(t => t.Key, s => s.Select(q => q.Value).ToHashSet());
foreach (var voter in voterPreferences)
{
// We want a list of everything each voter didn't vote for.
var unrankedChoices1 = taskVotes.Keys.Except(voter.Value);
foreach (var choice in voter.Value)
{
// Each choice matching or beating the ranks of other ranked choices is marked.
foreach (var otherChoice in voter.Value)
{
if ((choice != otherChoice) && (choice.MarkerValue <= otherChoice.MarkerValue))
{
pairwisePreferences[choiceIndexes[choice], choiceIndexes[otherChoice]]++;
}
}
// Each choice is ranked higher than all unranked choices
foreach (var nonChoice in unrankedChoices1)
{
pairwisePreferences[choiceIndexes[choice], choiceIndexes[nonChoice]]++;
}
}
}
return(pairwisePreferences);
}
/// <summary>
/// Gets the winning vote.
/// Excludes any already chosen votes from the process.
/// </summary>
/// <param name="voterRankings">The voter rankings.</param>
/// <param name="chosenChoices">The already chosen choices.</param>
/// <returns>Returns the winning vote.</returns>
private (VoteStorageEntry vote, double score) GetWinningVote(VoteStorage votes)
{
var workingVotes = new VoteStorage(votes);
int voterCount = workingVotes.SelectMany(a => a.Value).Distinct().Count();
int winCount = voterCount / 2 + 1;
while (workingVotes.Count > 1)
{
// Invert the votes so that we can look at preferences per user.
var voterPreferences = workingVotes
.SelectMany(v => v.Value)
.GroupBy(u => u.Key)
.ToDictionary(t => t.Key, s => s.Select(q => q.Value).OrderBy(r => r.MarkerValue).ToList());
// Check to see if we have a winner.
var(vote, count) = GetMostPreferredVote(voterPreferences);
if (count >= winCount)
{
var fullVote = workingVotes.First(a => a.Key == vote);
return(fullVote, count);
}
VoteLineBlock leastPreferredChoice;
// If not, eliminate the least preferred option and try again.
if (leastPreferredChecksFullVotes)
{
leastPreferredChoice = GetLeastPreferredChoice(workingVotes);
}
else
{
leastPreferredChoice = GetLeastPreferredChoice(voterPreferences);
}
workingVotes.Remove(leastPreferredChoice);
}
// If we get to here, the only option left has to win.
return(workingVotes.First(), 1);
}
CountVotesForTask(VoteStorage taskVotes)
{
var listOfChoices = taskVotes.Select(v => v.Key).ToList();
// Invert the votes so that we can look at preferences per user.
var voterPreferences = taskVotes
.SelectMany(v => v.Value)
.GroupBy(u => u.Key)
.ToDictionary(t => t.Key, s => s.Select(q => q.Value).OrderBy(r => r.MarkerValue).ToList());
int[,] pairwisePreferences = GetPairwisePreferences(voterPreferences, listOfChoices);
int[,] pairwiseWinners = GetPairwiseWinners(pairwisePreferences, listOfChoices.Count);
List <((int rank, double rankScore) ranking, VoteStorageEntry vote)> winningChoices =
GetResultsInOrder(pairwiseWinners, listOfChoices, taskVotes);
return(winningChoices);
}
