使用Linq计算平均值

Question

I am trying to write a query with Linq to calculate for a genre of a movie for a user (the most watched for that specific user) the average ranking of the movies for that genre (the rankings are in a different table and are given out by many users and I need to calculate the average ranking for each and every movie in that genre).

my scheme is this:

my code by now is this:

var extractMoviesAndTheirGenre =
                        from item in results join second in database.MovieGenres on item.movieId equals second.movieId
                        where item.movieId.Equals(second.movieId)
                        select new
                        {
                            MovieId = item.movieId,
                            GenreName = second.Genre.genreName,
                            GenreId = second.genreId
                        };
        var extractGenreNeeded =
                        from item in extractMoviesAndTheirGenre
                        group item by new
                        {
                            GenreName = item.GenreName,
                            GenreId = item.GenreId
                        }
                        into grouped
                        select new
                        {
                            GenreId = grouped.Key.GenreId,
                            GenreName = grouped.Key.GenreName,
                            CountGenre = grouped.Count(x => x.GenreId == grouped.Key.GenreId),
                        };
        extractGenreNeeded = (extractGenreNeeded.OrderByDescending(x => x.CountGenre).Take(1));
    var GenreId = extractGenreNeeded.FirstOrDefault().GenreId.ToString();
        var extractMoviesInFoundGenre =
                        from item in extractGenreNeeded
                        join second in database.MovieGenres on item.GenreId equals second.genreId
                        where second.genreId.Equals(GenreId)
                        select new
                        {
                            MovieId = second.movieId
                        };
        var extractingMoviesInGenreAndTheirAvarageRank =
                        from item in extractMoviesInFoundGenre
                        join second in database.UserMovieRanks on item.MovieId equals second.movieId
                        select new
                        {
                            MovieId = item.MovieId,
                            Rank = second.movieRank
                        };

As you can see, I was able to Isolate the most watched genre for the user(I get the list of movies watched by that user as an input to the query and this input is named results of type IQueryable) I am unable to calculate for each movie in that genre its average score...

Thank you,

Answer 1

You already have the Ranks for each Movie, so after your code

var extractingMoviesInGenreAndTheirAvarageRank =
        from item in extractMoviesInFoundGenre
        join second in database.UserMovieRanks on item.MovieId equals second.movieId
        select new
        {
            MovieId = item.MovieId,
            Rank = second.movieRank
        };

you should get the average, in this case with a lambda expression:

double avg = extractingMoviesInGenreAndTheirAvarageRank.Average(x => x.Rank);

Also, if you just want the average for every user, and don't care about MovieId , you could do everything in your first query:

var extractingMoviesInGenreAndTheirAvarageRank =
        (from item in extractMoviesInFoundGenre
        join second in database.UserMovieRanks on item.MovieId equals second.movieId
        select second.movieRank).Average();