Question

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. 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.

Answer 1

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()
                });