// TODO: Scalar preference relations based on Bradley-Terry model
public static PrefRelations CreateScalar(DataMatrix R)
{
int userCount = R.UserCount;
int itemCount = R.ItemCount;
PrefRelations PR = new PrefRelations(itemCount);
// Create a preference matrix for each user
Object lockMe = new Object();
Parallel.ForEach(R.Users, user =>
{
int userIndex = user.Item1;
RatingVector userRatings = new RatingVector(user.Item2);
Utils.PrintEpoch("Doing user/total", userIndex, userCount);
// The diagonal refer to the i-i item pair
SparseMatrix userPreferences = new SparseMatrix(itemCount);
// The diagonal is left empty!
//SparseMatrix.OfMatrix(Matrix.Build.SparseDiagonal(itemCount, Config.Preferences.EquallyPreferred));
// TODO: Use Vector.Map2 to replace the following two foreach loops
// Here we need to compare each pair of items rated by this user
foreach (Tuple <int, double> left in userRatings.Ratings)
{
int leftItemIndex = left.Item1;
double leftItemRating = left.Item2;
foreach (Tuple <int, double> right in userRatings.Ratings)
{
int rightItemIndex = right.Item1;
// TODO: We could compute only the lower triangular,
// and uppwer will be a negative mirror
// Let's do it directly at this stage
double rightItemRating = right.Item2;
Debug.Assert(rightItemRating != 0 && leftItemRating != 0);
// Skip the diagonal
if (leftItemIndex == rightItemIndex)
{
continue;
}
userPreferences[leftItemIndex, rightItemIndex] = 0.1 * (leftItemRating - rightItemRating + 5);//(double)leftItemRating / (leftItemRating + rightItemRating);
}
}
// Because pr's upper triangular should be a mirror of the lower triangular
Debug.Assert((userPreferences.NonZerosCount).IsEven());
double debug1 = (Math.Pow(((SparseVector)R.GetRow(userIndex)).NonZerosCount, 2)
- ((SparseVector)R.GetRow(userIndex)).NonZerosCount);
double debug2 = userPreferences.NonZerosCount;
Debug.Assert(debug1 == debug2);
lock (lockMe)
{
// Copy similarity values from lower triangular to upper triangular
//pr_uid = DenseMatrix.OfMatrix(pr_uid + pr_uid.Transpose() - DenseMatrix.CreateIdentity(pr_uid.RowCount));
PR[userIndex] = userPreferences;
}
});
return(PR);
}