/// <summary>
/// Predict all unknown values as global mean rating.
/// </summary>
public string RunGlobalMean()
{
if (!ReadyForNumerical)
{
GetReadyForNumerical();
}
StringBuilder log = new StringBuilder();
log.AppendLine(Utils.PrintHeading("Global Mean"));
// Prediction
Utils.StartTimer();
double globalMean = R_train.GetGlobalMean();
DataMatrix R_predicted = R_unknown.Multiply(globalMean);
log.AppendLine(Utils.StopTimer());
// Numerical Evaluation
log.AppendLine(Utils.PrintValue("RMSE", RMSE.Evaluate(R_test, R_predicted).ToString("0.0000")));
log.AppendLine(Utils.PrintValue("MAE", MAE.Evaluate(R_test, R_predicted).ToString("0.0000")));
return(log.ToString());
}
public static DataMatrix PredictRatings(PrefRelations PR_train,
DataMatrix R_unknown, int K, SimilarityData neighborsByUser)
{
Debug.Assert(PR_train.UserCount == R_unknown.UserCount);
Debug.Assert(PR_train.ItemCount == R_unknown.ItemCount);
// This matrix stores predictions
DataMatrix R_predicted = new DataMatrix(R_unknown.UserCount, R_unknown.ItemCount);
// This can be considered as the R_train in standard UserKNN
SparseMatrix positionMatrix = PR_train.GetPositionMatrix();
DataMatrix ratingMatrixFromPositions = new DataMatrix(positionMatrix);
Vector <double> meanByUser = ratingMatrixFromPositions.GetUserMeans();
Vector <double> meanByItem = ratingMatrixFromPositions.GetItemMeans();
double globalMean = ratingMatrixFromPositions.GetGlobalMean();
// Predict positions for each test user
// Appears to be very fast, parallel.foreach is unnecessary
foreach (Tuple <int, Vector <double> > user in R_unknown.Users)
{
int indexOfUser = user.Item1;
Vector <double> indexesOfUnknownRatings = user.Item2;
Utils.PrintEpoch("Predicting user/total", indexOfUser, PR_train.UserCount);
// Note that there are more than K neighbors in the list (sorted by similarity)
// we will use the top-K neighbors WHO HAVE RATED THE ITEM
// For example we have 200 top neighbors, and we hope there are
// K neighbors in the list have rated the item. We can't keep
// everyone in the neighbor list because there are too many for large data sets
var topNeighborsOfUser = neighborsByUser[indexOfUser];
double meanOfUser = meanByUser[indexOfUser];
// Loop through each position to be predicted
foreach (Tuple <int, double> unknownRating in indexesOfUnknownRatings.EnumerateIndexed(Zeros.AllowSkip))
{
int indexOfUnknownItem = unknownRating.Item1;
// Compute the position of this item for the user
// by combining neighbors' positions on this item
double weightedSum = 0;
double weightSum = 0;
int currentTopKCount = 0;
foreach (KeyValuePair <int, double> neighbor in topNeighborsOfUser)
{
int indexOfNeighbor = neighbor.Key;
double similarityOfNeighbor = neighbor.Value;
double itemPositionOfNeighbor = ratingMatrixFromPositions[indexOfNeighbor, indexOfUnknownItem];
// We count only if the neighbor has seen this item before
if (itemPositionOfNeighbor != 0)
{
// Recall that we use a constant to hold position value 0
// we revert it back here
if (itemPositionOfNeighbor == Config.ZeroInSparseMatrix)
{
Debug.Assert(true, "By using the PositionShift constant, we should not be in here.");
itemPositionOfNeighbor = 0;
}
weightSum += similarityOfNeighbor;
weightedSum += (itemPositionOfNeighbor - meanByUser[indexOfNeighbor]) * similarityOfNeighbor;
currentTopKCount++;
if (currentTopKCount >= K)
{
break;
}
}
}
// If any neighbor has seen this item
if (currentTopKCount != 0)
{
// TODO: Add user mean may improve the performance
R_predicted[indexOfUser, indexOfUnknownItem] = meanOfUser + weightedSum / weightSum;
}
else
{
R_predicted[indexOfUser, indexOfUnknownItem] = globalMean;
}
}
}//);
return(R_predicted);
}
public static DataMatrix PredictRatings(DataMatrix R_train, DataMatrix R_unknown,
int maxEpoch, double learnRate, double regularization, int factorCount)
{
int userCount = R_train.UserCount;
int itemCount = R_train.ItemCount;
int ratingCount = R_train.NonZerosCount;
double meanOfGlobal = R_train.GetGlobalMean();
DataMatrix R_train_unknown = R_train.IndexesOfNonZeroElements(); // For testing convergence
// User latent vectors with default seed
Matrix <double> P = Utils.CreateRandomMatrixFromNormal(userCount, factorCount, 0, 0.1, Config.Seed);
// Matrix<double> P = Utils.CreateRandomMatrixFromUniform(userCount, factorCount, 0, 0.1, Config.Seed);
// Item latent vectors with a different seed
Matrix <double> Q = Utils.CreateRandomMatrixFromNormal(factorCount, itemCount, 0, 0.1, Config.Seed + 1);
//Matrix<double> Q = Utils.CreateRandomMatrixFromUniform(factorCount, itemCount, 0, 0.1, Config.Seed + 1);
// SGD
double e_prev = double.MaxValue;
for (int epoch = 0; epoch < maxEpoch; ++epoch)
{
foreach (Tuple <int, int, double> element in R_train.Ratings)
{
int indexOfUser = element.Item1;
int indexOfItem = element.Item2;
double rating = element.Item3;
double e_ij = rating - (meanOfGlobal + P.Row(indexOfUser).DotProduct(Q.Column(indexOfItem)));
// Update feature vectors
Vector <double> P_u = P.Row(indexOfUser);
Vector <double> Q_i = Q.Column(indexOfItem);
Vector <double> P_u_updated = P_u + (Q_i.Multiply(e_ij) - P_u.Multiply(regularization)).Multiply(learnRate);
P.SetRow(indexOfUser, P_u_updated);
Vector <double> Q_i_updated = Q_i + (P_u.Multiply(e_ij) - Q_i.Multiply(regularization)).Multiply(learnRate);
Q.SetColumn(indexOfItem, Q_i_updated);
#region Update feature vectors loop version
/*
* // Update feature vectors
* for (int k = 0; k < factorCount; ++k)
* {
* double factorOfUser = P[indexOfUser, k];
* double factorOfItem = Q[k, indexOfItem];
*
* P[indexOfUser, k] += learnRate * (e_ij * factorOfItem - regularization * factorOfUser);
* Q[k, indexOfItem] += learnRate * (e_ij * factorOfUser - regularization * factorOfItem);
* }
*/
#endregion
}
// Display the current regularized error see if it converges
double e_curr = 0;
if (epoch == 0 || epoch == maxEpoch - 1 || epoch % (int)Math.Ceiling(maxEpoch * 0.1) == 4)
{
Matrix <double> predictedMatrix = R_train_unknown.PointwiseMultiply(P.Multiply(Q));
SparseMatrix correctMatrix = R_train.Matrix;
double squaredError = (correctMatrix - predictedMatrix).SquaredSum();
double regularizationPenaty = regularization * (P.SquaredSum() + Q.SquaredSum());
double objective = squaredError + regularizationPenaty;
#region Linear implementation
/*
* double e = 0;
* foreach (Tuple<int, int, double> element in R_train.Ratings)
* {
* int indexOfUser = element.Item1;
* int indexOfItem = element.Item2;
* double rating = element.Item3;
*
* e += Math.Pow(rating - P.Row(indexOfUser).DotProduct(Q.Column(indexOfItem)), 2);
*
* for (int k = 0; k < factorCount; ++k)
* {
* e += (regularization / 2) * (Math.Pow(P[indexOfUser, k], 2) + Math.Pow(Q[k, indexOfItem], 2));
* }
* }
*/
#endregion
// Record the current error
e_curr = objective;
// Stop the learning if the regularized error falls below a certain threshold
if (e_prev - e_curr < 0.001)
{
Console.WriteLine("Improvment less than 0.001, learning stopped.");
break;
}
e_prev = e_curr;
Utils.PrintEpoch("Epoch", epoch, maxEpoch, "Objective cost", objective);
}
}
SparseMatrix R_predicted = new SparseMatrix(R_unknown.UserCount, R_unknown.ItemCount);
foreach (var element in R_unknown.Matrix.EnumerateIndexed(Zeros.AllowSkip))
{
int indexOfUser = element.Item1;
int indexOfItem = element.Item2;
double r_predicted = meanOfGlobal + P.Row(indexOfUser) * Q.Column(indexOfItem);
if (r_predicted > Config.Ratings.MaxRating)
{
r_predicted = Config.Ratings.MaxRating;
}
if (r_predicted < Config.Ratings.MinRating)
{
r_predicted = Config.Ratings.MinRating;
}
R_predicted[indexOfUser, indexOfItem] = r_predicted;
}
return(new DataMatrix(R_predicted));
//return new RatingMatrix(R_unknown.PointwiseMultiply(P.Multiply(Q)));
}
