private BookScore EvaluateScore(IEnumerable <UsersSimilarity> similarUsers, BookScore bookScore,
double meanRateForUser)
{
var scoreNumerator = 0.0;
var scoreDenominator = 0.0;
var rate = 0.0;
foreach (var u in similarUsers)
{
var book = u.BooksUniqueForComparedUser.FirstOrDefault(x => x.BookId == bookScore.BookId);
if (book == null || u.AverageScoreForComparedUser == null || u.Similarity == null)
{
continue;
}
scoreNumerator += (book.Rate - u.AverageScoreForComparedUser.Value) * u.Similarity.Value;
scoreDenominator += Math.Abs(u.Similarity.Value);
}
if (scoreDenominator != 0)
{
rate = scoreNumerator / scoreDenominator + meanRateForUser;
}
bookScore.PredictedRate = Math.Round(rate, 2);
return(bookScore);
}
private List <BookScore> GetAllRecommendedBooksForUser(List <UsersSimilarity> similarUsers, int userId,
string[] booksIds)
{
if (similarUsers == null || similarUsers?.Count == 0)
{
return(null);
}
var recommendedBooks = new List <BookScore>();
if (booksIds.Length == 0)
{
PersistRecommendedBooksInDb(null, userId);
return(null);
}
var meanRateForUser = _context.GetAverageRateForUser(userId) ?? 0;
foreach (var id in booksIds)
{
var temp = new BookScore
{
UserId = userId,
BookId = id
};
var bookScore = EvaluateScore(similarUsers, temp, meanRateForUser);
if (bookScore != null)
{
recommendedBooks.Add(bookScore);
}
}
return(recommendedBooks.OrderByDescending(x => x.PredictedRate).ToList());
}
public BookScore[] CreateBookScores(int userId, string[] isbn, short[] rates, double[] predictedRates = null)
{
var results = new BookScore[isbn.Length];
for (int i = 0; i < isbn.Length; i++)
{
var predictedRate = predictedRates == null?RandomNumber(1) : predictedRates[i];
results[i] = new BookScore
{
UserId = userId,
BookId = isbn[i],
Rate = rates[i],
PredictedRate = predictedRate
};
}
return(results);
}
public void BookScoreComparer_ShouldReturnLower(int userId, string bookId, double predictedRate)
{
var x = new BookScore
{
UserId = 1,
BookId = "1",
PredictedRate = 5,
Rate = 23
};
var y = new BookScore
{
UserId = userId,
BookId = bookId,
PredictedRate = predictedRate,
Rate = 23
};
_sut.Compare(x, y).ShouldBe(-1);
}
