Linq按两个字段分组并取平均值 [英] Linq to group by two fields and average

问题描述

我有以下C#模型:

public class RawData
{
    public int questionnaireId { get; set; }

    public int coachNodeId { get; set; }

    public int questionnaireNumber { get; set; }

    public float score { get; set; }
}

public class AveragedData
{
    public int coachNodeId { get; set; }

    public int questionnaireNumber { get; set; }

    public float averageScore { get; set; }
}

我有一个API端点，该端点从数据库返回数据，映射为List<RawData>.值是这样的:

I have an API endpoint which is returning data from a database, mapped as List<RawData>. The values are like this:

questionnaireId | coachNodeId | questionnaireNumber | score
1               | 30          | 1                   | 2
2               | 40          | 1                   | 3
3               | 30          | 2                   | 1
4               | 30          | 3                   | 4
5               | 40          | 2                   | 5
6               | 40          | 1                   | 5
7               | 30          | 1                   | 1
8               | 30          | 1                   | 2
9               | 40          | 1                   | 2
10              | 30          | 2                   | 4

在LINQ查询中，我现在要做的是对由coachNodeId和questionnaireNumber分组的score值取平均值，并返回类型为AveragedData的列表.

What I need to do now, in a LINQ query, is to average out the score values grouped by coachNodeId and questionnaireNumber and return a list of type AveragedData.

对以上示例数据进行平均和分组后返回的值应为:

The values returned by averaging and grouping the example data above, should be:

coachNodeId | questionnaireNumber | averageScore
30          | 1                   | 1.66666666          (calculated by: (2 + 1 + 2) / 3))
30          | 2                   | 2.5                 (calculated by: (1 + 4) / 2))
30          | 3                   | 4                   (calculated by: (4 / 1))
40          | 1                   | 3.33333333          (calculated by: (3 + 5 + 2) / 3))
40          | 2                   | 5                   (calculated by: (5 / 1))

我对LINQ不熟悉，因此很难将查询组合在一起，将查询按coachNodeId和questionnaireNumber分组并取平均分，返回类型为List<AveragedData>的对象.有人可以建议如何做到这一点吗?

I'm not experienced with LINQ so am struggling to put together a query that groups by both coachNodeId and questionnaireNumber and averages the score, returning an object of type List<AveragedData>. Could anyone suggest how to accomplish this?

非常感谢.

推荐答案

假设您有一个名为list的List<RawData>，那么您想要的是

assuming you have a List<RawData> called list, you are wanting:

var results = list.GroupBy(x => new
                                {
                                     questionnaire = x.questionnaireId,
                                     coach = x.coachNodeId
                                })
                  .Select(x => new AveragedData
                                {
                                     coachNodeId = x.Key.coach,
                                     questionnaireNumber = x.Key.questionnaire,
                                     averageScore = x.Average(xx => xx.score)
                                })
                  .ToList();

进行分组，然后使用Select以及LINQ的Average将数据投影到您的类型.

Do the grouping, then use a Select to project the data to your type, using LINQ's Average as well.

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