/**
* Builds L2-regularized classifiers for a sequence of regularization parameter lambdas.
*
* @param trainSet the training set.
* @param isSparse <code>true</code> if the training set is treated as sparse.
* @param maxNumIters the maximum number of iterations.
* @param lambdas the lambdas array.
* @return L2-regularized binary classifiers.
*/
public GLM[] buildClassifiers(
Instances trainSet, boolean isSparse, int maxNumIters, double[] lambdas) {
Attribute classAttribute = trainSet.getTargetAttribute();
if (classAttribute.getType() != Attribute.Type.NOMINAL) {
throw new IllegalArgumentException("Class attribute must be nominal.");
}
NominalAttribute clazz = (NominalAttribute) classAttribute;
int numClasses = clazz.getStates().length;
if (isSparse) {
SparseDataset sd = getSparseDataset(trainSet, true);
int[] attrs = sd.attrs;
int[][] indices = sd.indices;
double[][] values = sd.values;
double[] y = new double[sd.y.length];
double[] cList = sd.cList;
if (numClasses == 2) {
for (int i = 0; i < y.length; i++) {
int label = (int) sd.y[i];
y[i] = label == 0 ? 1 : 0;
}
GLM[] glms = buildBinaryClassifiers(attrs, indices, values, y, maxNumIters, lambdas);
for (GLM glm : glms) {
double[] w = glm.w[0];
for (int j = 0; j < cList.length; j++) {
int attIndex = attrs[j];
w[attIndex] *= cList[j];
}
}
return glms;
} else {
int p = attrs.length == 0 ? 0 : (StatUtils.max(attrs) + 1);
GLM[] glms = new GLM[lambdas.length];
for (int i = 0; i < glms.length; i++) {
glms[i] = new GLM(numClasses, p);
}
for (int k = 0; k < numClasses; k++) {
// One-vs-the-rest
for (int i = 0; i < y.length; i++) {
int label = (int) sd.y[i];
y[i] = label == k ? 1 : 0;
}
GLM[] binaryClassifiers =
buildBinaryClassifiers(attrs, indices, values, y, maxNumIters, lambdas);
for (int l = 0; l < glms.length; l++) {
GLM binaryClassifier = binaryClassifiers[l];
GLM glm = glms[l];
double[] w = binaryClassifier.w[0];
for (int j = 0; j < cList.length; j++) {
int attIndex = attrs[j];
glm.w[k][attIndex] = w[attIndex] * cList[j];
}
glm.intercept[k] = binaryClassifier.intercept[0];
}
}
return glms;
}
} else {
DenseDataset dd = getDenseDataset(trainSet, true);
int[] attrs = dd.attrs;
double[][] x = dd.x;
double[] y = new double[dd.y.length];
double[] cList = dd.cList;
if (numClasses == 2) {
for (int i = 0; i < y.length; i++) {
int label = (int) dd.y[i];
y[i] = label == 0 ? 1 : 0;
}
GLM[] glms = buildBinaryClassifiers(attrs, x, y, maxNumIters, lambdas);
for (GLM glm : glms) {
double[] w = glm.w[0];
for (int j = 0; j < cList.length; j++) {
int attIndex = attrs[j];
w[attIndex] *= cList[j];
}
}
return glms;
} else {
int p = attrs.length == 0 ? 0 : attrs[attrs.length - 1] + 1;
GLM[] glms = new GLM[lambdas.length];
for (int i = 0; i < glms.length; i++) {
glms[i] = new GLM(numClasses, p);
}
for (int k = 0; k < numClasses; k++) {
// One-vs-the-rest
for (int i = 0; i < y.length; i++) {
int label = (int) dd.y[i];
y[i] = label == k ? 1 : 0;
}
GLM[] binaryClassifiers = buildBinaryClassifiers(attrs, x, y, maxNumIters, lambdas);
for (int l = 0; l < glms.length; l++) {
GLM binaryClassifier = binaryClassifiers[l];
GLM glm = glms[l];
double[] w = binaryClassifier.w[0];
for (int j = 0; j < cList.length; j++) {
int attIndex = attrs[j];
glm.w[k][attIndex] = w[attIndex] * cList[j];
}
glm.intercept[k] = binaryClassifier.intercept[0];
}
}
return glms;
}
}
}
