Get Average Using LINQ

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  
            };  

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. 开发者_如何转开发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.

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double RatingAverage = ctx.Rates.Where(r => r.Id == Id).Average(r => r.Rating);

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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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This could also work if you don't want to calculate the average separately and rating is from another table

var query = (from u in db.Users 
                     where rating.Id == Id
                     select new ViewModel
                     {
                         UserId = rating.UserId
                         Rating = (from c in db.Comments where c.fkUserId.Equals(u.Id) select c.StarRating).Average()
                     }).ToList();
        return query;

It will return rating average. Note: Use Rating as nullable double type i.e. double? Rating