private static IEnumerable <KeyValuePair <string, double> > GetTopMatches(Dictionary <string, Dictionary <string, double> > preferences,
string prefKey, IScoreMetric metric, int count)
{
var scores = new Dictionary <string, double>();
foreach (var prefPair in preferences)
{
if (prefPair.Key == prefKey)
{
continue;
}
double score = Calculate(preferences[prefKey], prefPair.Value, metric);
scores.Add(prefPair.Key, score);
}
var result = new List <KeyValuePair <string, double> >(count);
foreach (var t in scores.OrderByDescending(x => x.Value).Take(count))
{
result.Add(t);
}
return(result);
}
public static double Calculate(Dictionary <string, double> firstPref, Dictionary <string, double> secondPref, IScoreMetric metric)
{
var common = firstPref.Keys.Intersect(secondPref.Keys).ToList();
if (common.Count == 0)
{
return(0);
}
var prefs = new Dictionary <string, (double, double)>();
foreach (var key in common)
{
prefs.Add(key, (firstPref[key], secondPref[key]));
}
return(metric.Calculate(prefs));
}
public static IEnumerable <KeyValuePair <string, double> > GetSimilarItems(Dictionary <string, Dictionary <string, double> > preferences,
string itemName, IScoreMetric metric, int itemsCount)
{
var transformedPrefs = new Dictionary <string, Dictionary <string, double> >();
foreach (var prefPair in preferences)
{
foreach (var item in prefPair.Value)
{
if (!transformedPrefs.ContainsKey(item.Key))
{
transformedPrefs[item.Key] = new Dictionary <string, double>();
}
transformedPrefs[item.Key].Add(prefPair.Key, item.Value);
}
}
return(GetTopMatches(transformedPrefs, itemName, metric, itemsCount));
}
public static IEnumerable <KeyValuePair <string, double> > GetRecommendations(Dictionary <string, Dictionary <string, double> > preferences,
string personName, IScoreMetric metric, int usersCount)
{
var totals = new Dictionary <string, double>();
var scoresSums = new Dictionary <string, double>();
var personScores = preferences[personName];
foreach (var prefPair in preferences)
{
if (prefPair.Key == personName)
{
continue;
}
double score = Calculate(personScores, prefPair.Value, metric);
if (score <= 0)
{
continue;
}
foreach (var movie in prefPair.Value)
{
if (!personScores.ContainsKey(movie.Key))
{
double total = 0.0;
totals.TryGetValue(movie.Key, out total);
totals[movie.Key] = total + movie.Value * score;
double scoreSum;
scoresSums.TryGetValue(movie.Key, out scoreSum);
scoresSums[movie.Key] = scoreSum + score;
}
}
}
var result = new List <KeyValuePair <string, double> >();
foreach (var item in totals)
{
result.Add(new KeyValuePair <string, double>(item.Key, item.Value / scoresSums[item.Key]));
}
return(result.OrderByDescending(x => x.Value).Take(usersCount));
}
public static IEnumerable <KeyValuePair <string, double> > GetUsersWithSimilarTaste(Dictionary <string, Dictionary <string, double> > preferences,
string personName, IScoreMetric metric, int usersCount)
{
return(GetTopMatches(preferences, personName, metric, usersCount));
}
