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package com.shijingsh.ai.evaluate.ranking;

import com.shijingsh.ai.evaluate.RankingEvaluator;
import com.shijingsh.ai.math.structure.matrix.SymmetryMatrix;

import com.shijingsh.ai.evaluate.RankingEvaluator;
import com.shijingsh.ai.math.structure.matrix.SymmetryMatrix;
import it.unimi.dsi.fastutil.ints.IntList;
import it.unimi.dsi.fastutil.ints.IntSet;

/**
 * 多样性评估器
 *
 * @author Birdy
 */
public class DiversityEvaluator extends RankingEvaluator {

    private SymmetryMatrix similarityMatrix;

    public DiversityEvaluator(int size, SymmetryMatrix similarityMatrix) {
        super(size);
        this.similarityMatrix = similarityMatrix;
    }

    @Override
    protected float measure(IntSet checkCollection, IntList rankList) {
        if (rankList.size() > size) {
            rankList = rankList.subList(0, size);
        }
        float diversity = 0F;
        int size = rankList.size();
        for (int indexOut = 0; indexOut < size; indexOut++) {
            for (int indexIn = indexOut + 1; indexIn < size; indexIn++) {
                int itemOut = rankList.get(indexOut);
                int itemIn = rankList.get(indexIn);
                diversity += 1F - similarityMatrix.getValue(itemOut, itemIn);
                diversity += 1F - similarityMatrix.getValue(itemIn, itemOut);
            }
        }
        return diversity / (size * (size - 1));
    }

}