c# - groupby - Average extension method in Linq for default value

linq groupby average (2)

Anyone know how I can set a default value for an average? I have a line like this...

dbPlugins = (from p in dbPlugins
                select new { Plugin = p, AvgScore = p.DbVersions.Average(x => x.DbRatings.Average(y => y.Score)) })
            .OrderByDescending(x => x.AvgScore)
            .Select(x => x.Plugin).ToList();

which throws an error becase I have no ratings yet. If I have none I want the average to default to 0. I was thinking this should be an extension method where I could specify what the default value should be.


I don't think there's a way to select default, but how about this query

dbPlugins = (from p in dbPlugins
             select new { 
                Plugin = p, AvgScore = 
                    p.DbVersions.Any(x => x.DbRatings) ?
                        p.DbVersions.Average(x => x.DbRatings.Average(y => y.Score)) : 0 })
             .OrderByDescending(x => x.AvgScore)
             .Select(x => x.Plugin).ToList();

Essentially the same as yours, but we first ask if there are any ratings before averaging them. If not, we return 0.

I tried some of those answers but ended up getting more exceptions for one reason or another. this ended up working for me. I am sure the performance is aweful but I will revise later.

var q1 = from v in db.DbVersions select new { VersionId = v.Id, AvgScore = v.DbRatings.Average(x => x.Score) as Nullable<double> };
var q2 = from p in dbPlugins select new { Plugin = p, AvgScore = q1.Where(x => p.DbVersions.Select(y => y.Id).Contains(x.VersionId)).Average(x => x.AvgScore) as Nullable<double> };
dbPlugins = q2.OrderByDescending(x => x.AvgScore).Select(x => x.Plugin).ToList();