public override double CalculateError(IRecommendation recommendation, IEnumerable <IRating> ratings, IEnumerable <IRater> raters, IEnumerable <ISubject> subjects)
{
var sum = 0D;
var count = 0;
foreach (var rating in ratings)
{
var value = recommendation.RecommendSubject(rating.Rater, rating.Subject);
if (value == null)
{
continue;
}
var diff = value.Value - rating.Value;
sum += Math.Abs(diff);
++count;
}
;
if (count == 0)
{
return(-1);
}
var error = sum / count;
return(error);
}
public IRating RecommendSubject(IRater rater, ISubject subject)
{
var key = CreateCacheKey(rater, subject);
var cachedValue = 0D;
if (_cache.TryGetValue(key, out cachedValue))
{
return(new SimpleRating(rater, subject, cachedValue));
}
var rating = _algorithm.RecommendSubject(rater, subject);
if (rating != null)
{
_cache[key] = rating.Value;
}
return(rating);
}
