io.github.oliviercailloux.j_voting.preferences.analysis.FrenchElection Maven / Gradle / Ivy

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General classes for dealing with social choice theory.
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package io.github.oliviercailloux.j_voting.preferences.analysis;

import java.util.Collections;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.stream.Collectors;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Maps;
import com.google.common.collect.Sets;

import io.github.oliviercailloux.j_voting.Alternative;
import io.github.oliviercailloux.j_voting.Voter;
import io.github.oliviercailloux.j_voting.preferences.ImmutableLinearPreference;

public class FrenchElection {

	private ImmutableSet alternatives;
	private ImmutableSet voters;
	private Map scores;
	private ImmutableSet winners;
	private static final Logger LOGGER = LoggerFactory.getLogger(FrenchElection.class.getName());

	/**
	 * 
	 * @param linearPreferences  not null 
	 * @return new FrenchElection
	 */
	public static FrenchElection asFrenchElection(Set linearPreferences) {
		LOGGER.debug("FrenchElection Factory");
		Preconditions.checkNotNull(linearPreferences);
		return new FrenchElection(linearPreferences);
	}

	/**
	 * 
	 * @param linearPreferences  not null 
	 * @return new FrenchElection
	 */
	private FrenchElection(Set linearPreferences) {
		LOGGER.debug("FrenchElection Constructor");
		Map tmpScores = Maps.newHashMap();
		Set tmpVoters = Sets.newHashSet();
		for (ImmutableLinearPreference linearPreference : linearPreferences) {
			if (!tmpVoters.add(linearPreference.getVoter()))
				throw new IllegalArgumentException("A voter can't vote two times in a same election");
			for (Alternative alternative : linearPreference.getAlternatives())
				tmpScores.putIfAbsent(alternative, 0);
			Alternative tmpAlternative = linearPreference.asList().get(0);
			Integer votes = (tmpScores.get(tmpAlternative) != null) ? tmpScores.get(tmpAlternative) : 0;
			tmpScores.put(tmpAlternative, votes + 1);
		}
		this.winners = ImmutableSet
				.copyOf(tmpScores.entrySet().stream()
						.filter(entry -> Collections
								.max(tmpScores.entrySet(),
										(Entry e1, Entry e2) -> e1
												.getValue().compareTo(e2.getValue()))
								.getValue().equals(entry.getValue()))
						.map(Map.Entry::getKey).collect(Collectors.toSet()));
		this.scores = tmpScores;
		this.alternatives = ImmutableSet.copyOf(tmpScores.keySet());
		this.voters = ImmutableSet.copyOf(tmpVoters);
	}

	public ImmutableSet getWinners() {
		return winners;
	}

	public ImmutableSet getAlternatives() {
		return alternatives;
	}

	public Map getScores() {
		return scores;
	}

	public ImmutableSet getVoters() {
		return voters;
	}
}