private static double DoComputeSimilarity(User u1, User u2)
{
IEnumerable<Movie> common = u1.Ratings.Keys.Intersect(u2.Ratings.Keys);
int count = common.Count();
if (count < 2) return 0;
double sum1 = 0;
double sum2 = 0;
double sumProd = 0;
double sumSquare1 = 0;
double sumSquare2 = 0;
foreach (var m in common)
{
int r1 = u1.Ratings[m];
int r2 = u2.Ratings[m];
sum1 += r1;
sum2 += r2;
sumProd += r1 * r2;
sumSquare1 += (r1 * r1);
sumSquare2 += (r2 * r2);
}
double numerator = sumProd - (sum1 * sum2) / count;
double denominator = Math.Sqrt((sumSquare1 - (sum1 * sum1) / count) * (sumSquare2 - (sum2 * sum2) / count));
if (denominator < Double.Epsilon) return 0;
double s = numerator / denominator;
if (s < -1) return -1;
if (s > 1) return 1;
return s;
}
public double SimilarityPearson(User u1, User u2)
{
if (u1 == u2) return 1.0;
double result;
if (_similarities.TryGetValue(new KeyPair(u1, u2), out result))
{
return result;
}
result = DoComputeSimilarity(u1, u2);
_similarities.Add(new KeyPair(u1, u2), result);
return result;
}
public static void ReadRatings( User[] users, Movie[] movies, string path )
{
using( TextReader r = File.OpenText( path ) )
{
string line;
while( (line = r.ReadLine()) != null )
{
string[] cells = line.Split( CellSeparator, StringSplitOptions.None );
int idUser = int.Parse( cells[0] );
int idMovie = int.Parse( cells[1] );
if( idMovie >= 0 && idMovie < movies.Length
&& idUser >= 0 && idUser < users.Length )
{
users[idUser].Ratings.Add( movies[idMovie], int.Parse( cells[2] ) );
}
}
}
}
public static void ReadUsers( string path, out Dictionary<int,User> first, out Dictionary<int,List<User>> duplicates )
{
first = new Dictionary<int, User>();
duplicates = new Dictionary<int, List<User>>();
using( TextReader r = File.OpenText( path ) )
{
string line;
while( (line = r.ReadLine()) != null )
{
User exists, u = new User( line );
if( first.TryGetValue( u.UserID, out exists ) )
{
List<User> list;
if( !duplicates.TryGetValue( u.UserID, out list ) )
{
list = new List<User>();
duplicates.Add( u.UserID, list );
}
list.Add( u );
}
else first.Add( u.UserID, u );
}
}
}
public KeyPair(User u1, User u2)
{
U1 = u1;
U2 = u2;
}
public BestFUser( User u, double s )
{
FUser = u;
Similarity = s;
}