使用 LINQ 获取平均值 [英] Get Average Using LINQ

问题描述

希望有人可以帮助我使用 LINQ 语法来计算平均值.例如，我有以下 LINQ 查询:

Hoping someone can help me with the LINQ syntax to calculate an average. For example, I have the following LINQ query:

var rates = from rating in ctx.Rates  
            where rating.Id == Id  
            select new 
            {   
                UserId = rating.UserId,  
                Rating = rating.Rating  
            };  

如果返回 10 条记录，我需要计算 Rating 字段的平均值.它在我的数据库中被定义为 Double .我正在使用 LINQ to EF.因此，我将分配 UserId、MiscId，而 Rating 将是返回记录的平均值.我将一个对象传递回客户端代码.

If 10 records are returned, I need to calculate average on the Rating field. It is defined as as a Double in my DB. I am using LINQ to EF. So I would be assigning the UserId, MiscId, and the Rating would be the average on the records returned. I am passing one object back to the client code.

推荐答案

您是否正在寻找每个用户 ID 的平均评分?如果是这样，那么您需要同时使用 GroupBy 和 平均值.

Are you looking for an average rating per user id? If so, then you need to use both GroupBy and Average.

var rates = ctx.Rates
               .Where( r => r.Id == Id )
               .GroupBy( g => g.UserId, r => r.Rating )
               .Select( g => new
                {
                   UserId = g.Key,
                   Rating = g.Average()
                }); 

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