/// <summary>
/// Calculates absolute error between prediction and ground truth
/// </summary>
/// <param name="testSource">A source of ratings made by users</param>
/// <param name="mapping">A mapping to convert source ratings into experiment specific ones</param>
/// <param name="predictions">Ratings which are predicted by the recommender</param>
/// <returns></returns>
private static Dictionary <Movie, List <double> > PredictionError(
SplitInstanceSource <string> testSource,
IStarRatingRecommenderMapping <SplitInstanceSource <string>, RatingTriple, string, Movie, int, NoFeatureSource, Vector> mapping,
IDictionary <string, IDictionary <Movie, IDictionary <int, double> > > predictions)
{
var evMapping = mapping.ForEvaluation();
var allErrors = new Dictionary <Movie, List <double> >();
foreach (var userWithPredictionList in predictions)
{
foreach (var itemPrediction in userWithPredictionList.Value)
{
var prediction = itemPrediction.Value;
var groundTruth = evMapping.GetRating(testSource, userWithPredictionList.Key, itemPrediction.Key);
var predictedRating = prediction.Aggregate((l, r) => l.Value > r.Value ? l : r).Key;
var error = Math.Abs(groundTruth - predictedRating);
if (allErrors.TryGetValue(itemPrediction.Key, out var values))
{
values.Add(error);
}
else
{
allErrors.Add(itemPrediction.Key, new List <double>()
{
error
});
}
}
}
return(allErrors);
}
/// <summary>
/// Takes test data from data source and represents it in the form of jagged array.
/// The first dimension represents users, the second dimension represents movies.
/// </summary>
/// <param name="mapping">A mapping to convert ratings to a scale used exactly in the current experiment. </param>
/// <returns></returns>
public double[][] GetGroundTruth(
IStarRatingRecommenderMapping <SplitInstanceSource <string>, RatingTriple, string, Movie, int, NoFeatureSource, Vector> mapping
)
{
Rand.Restart(RandomSeed);
var testSource = SplitInstanceSource.Test(RatingsPath);
var mappingForEvaluation = mapping.ForEvaluation();
var users = mappingForEvaluation.GetUsers(testSource);
var ratings = users.Select(u =>
mappingForEvaluation.GetItemsRatedByUser(testSource, u)
.Select(m => (double)mappingForEvaluation.GetRating(testSource, u, m)));
var groundTruthArray = GetJaggedDoubles(ratings);
return(groundTruthArray);
}