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package com.shijingsh.ai.evaluate.ranking;

import com.shijingsh.ai.evaluate.RankingEvaluator;

import com.shijingsh.ai.evaluate.RankingEvaluator;
import it.unimi.dsi.fastutil.ints.IntList;
import it.unimi.dsi.fastutil.ints.IntSet;

/**
 * 平均倒数排名评估器
 *
 *  * MRR = Mean Reciprocal Rank(平均倒数排名)
 * https://en.wikipedia.org/wiki/Mean_reciprocal_rank
 * 
 *
 * @author Birdy
 */
public class MRREvaluator extends RankingEvaluator {

    public MRREvaluator(int size) {
        super(size);
    }

    @Override
    protected float measure(IntSet checkCollection, IntList rankList) {
        if (rankList.size() > size) {
            rankList = rankList.subList(0, size);
        }
        int size = rankList.size();
        for (int index = 0; index < size; index++) {
            int itemIndex = rankList.get(index);
            if (checkCollection.contains(itemIndex)) {
                return 1F / (index + 1);
            }
        }
        return 0F;
    }

}