@Override
protected void buildModel() throws Exception {
for (int iter = 1; iter <= numIters; iter++) {
loss = 0;
errs = 0;
for (int s = 0, smax = numUsers * 100; s < smax; s++) {
// randomly draw (u, i, j)
int u = 0, i = 0, j = 0;
while (true) {
u = Randoms.uniform(numUsers);
SparseVector pu = userCache.get(u);
if (pu.getCount() == 0) continue;
int[] is = pu.getIndex();
i = is[Randoms.uniform(is.length)];
do {
j = Randoms.uniform(numItems);
} while (pu.contains(j));
break;
}
// update parameters
double xui = predict(u, i);
double xuj = predict(u, j);
double xuij = xui - xuj;
double vals = -Math.log(g(xuij));
loss += vals;
errs += vals;
double cmg = g(-xuij);
for (int f = 0; f < numFactors; f++) {
double puf = P.get(u, f);
double qif = Q.get(i, f);
double qjf = Q.get(j, f);
P.add(u, f, lRate * (cmg * (qif - qjf) - regU * puf));
Q.add(i, f, lRate * (cmg * puf - regI * qif));
Q.add(j, f, lRate * (cmg * (-puf) - regI * qjf));
loss += regU * puf * puf + regI * qif * qif + regI * qjf * qjf;
}
}
if (isConverged(iter)) break;
}
}
/**
* Split ratings into k-fold.
*
* @param kfold number of folds
*/
private void splitFolds(int kfold) {
assert kfold > 0;
assignMatrix = new SparseMatrix(rateMatrix);
int numRates = rateMatrix.getData().length;
numFold = kfold > numRates ? numRates : kfold;
// divide rating data into kfold sample of equal size
double[] rdm = new double[numRates];
int[] fold = new int[numRates];
double indvCount = (numRates + 0.0) / numFold;
for (int i = 0; i < numRates; i++) {
rdm[i] = Randoms.uniform(); // Math.random();
fold[i] = (int) (i / indvCount) + 1; // make sure that each fold has each size sample
}
Sortor.quickSort(rdm, fold, 0, numRates - 1, true);
int[] row_ptr = rateMatrix.getRowPointers();
int[] col_idx = rateMatrix.getColumnIndices();
int f = 0;
for (int u = 0, um = rateMatrix.numRows(); u < um; u++) {
for (int idx = row_ptr[u], end = row_ptr[u + 1]; idx < end; idx++) {
int j = col_idx[idx];
// if randomly put an int 1-5 to entry (u, j), we cannot make sure equal size for each fold
assignMatrix.set(u, j, fold[f++]);
}
}
}
