Java List<EvaluationItemRecordDTO> 按照evaluationItemId分组 按照score求平均值最后求和

以下是Java代码示例，实现按照evaluationItemId分组，按照score求平均值，最后求和：

import java.util.*;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        // 假设有以下评估记录
        List<EvaluationItemRecordDTO> records = new ArrayList<>();
        records.add(new EvaluationItemRecordDTO(1, 80));
        records.add(new EvaluationItemRecordDTO(2, 90));
        records.add(new EvaluationItemRecordDTO(1, 70));
        records.add(new EvaluationItemRecordDTO(1, 85));
        records.add(new EvaluationItemRecordDTO(2, 95));

        // 按照evaluationItemId分组，按照score求平均值
        Map<Integer, Double> avgScoreByItemId = records.stream()
                .collect(Collectors.groupingBy(
                        EvaluationItemRecordDTO::getEvaluationItemId,
                        Collectors.averagingDouble(EvaluationItemRecordDTO::getScore)));

        // 输出每个评估项的平均分数
        System.out.println("每个评估项的平均分数：");
        for (Map.Entry<Integer, Double> entry : avgScoreByItemId.entrySet()) {
            System.out.println("评估项" + entry.getKey() + "的平均分数为：" + entry.getValue());
        }

        // 求所有评估项平均分数的总和
        double sumOfAvgScores = avgScoreByItemId.values().stream()
                .mapToDouble(Double::doubleValue)
                .sum();
        System.out.println("所有评估项平均分数的总和为：" + sumOfAvgScores);
    }
}

class EvaluationItemRecordDTO {
    private int evaluationItemId;
    private int score;

    public EvaluationItemRecordDTO(int evaluationItemId, int score) {
        this.evaluationItemId = evaluationItemId;
        this.score = score;
    }

    public int getEvaluationItemId() {
        return evaluationItemId;
    }

    public void setEvaluationItemId(int evaluationItemId) {
        this.evaluationItemId = evaluationItemId;
    }

    public int getScore() {
        return score;
    }

    public void setScore(int score) {
        this.score = score;
    }
}

输出结果为：

每个评估项的平均分数：
评估项1的平均分数为：78.33333333333333
评估项2的平均分数为：92.5
所有评估项平均分数的总和为：170.83333333333334