/**
* Buildclassifier selects a classifier from the set of classifiers by minimising error on the
* training data.
*
* @param data the training data to be used for generating the boosted classifier.
* @exception Exception if the classifier could not be built successfully
*/
public void buildClassifier(Instances data) throws Exception {
if (m_Classifiers.length == 0) {
throw new Exception("No base classifiers have been set!");
}
Instances newData = new Instances(data);
newData.deleteWithMissingClass();
newData.randomize(new Random(m_Seed));
if (newData.classAttribute().isNominal() && (m_NumXValFolds > 1))
newData.stratify(m_NumXValFolds);
Instances train = newData; // train on all data by default
Instances test = newData; // test on training data by default
Classifier bestClassifier = null;
int bestIndex = -1;
double bestPerformance = Double.NaN;
int numClassifiers = m_Classifiers.length;
for (int i = 0; i < numClassifiers; i++) {
Classifier currentClassifier = getClassifier(i);
Evaluation evaluation;
if (m_NumXValFolds > 1) {
evaluation = new Evaluation(newData);
for (int j = 0; j < m_NumXValFolds; j++) {
train = newData.trainCV(m_NumXValFolds, j);
test = newData.testCV(m_NumXValFolds, j);
currentClassifier.buildClassifier(train);
evaluation.setPriors(train);
evaluation.evaluateModel(currentClassifier, test);
}
} else {
currentClassifier.buildClassifier(train);
evaluation = new Evaluation(train);
evaluation.evaluateModel(currentClassifier, test);
}
double error = evaluation.errorRate();
if (m_Debug) {
System.err.println(
"Error rate: "
+ Utils.doubleToString(error, 6, 4)
+ " for classifier "
+ currentClassifier.getClass().getName());
}
if ((i == 0) || (error < bestPerformance)) {
bestClassifier = currentClassifier;
bestPerformance = error;
bestIndex = i;
}
}
m_ClassifierIndex = bestIndex;
m_Classifier = bestClassifier;
if (m_NumXValFolds > 1) {
m_Classifier.buildClassifier(newData);
}
}
public void split() throws IOException {
FileSystem fs = FileSystem.get(new Configuration());
fs.delete(splitsDir, true);
instances.randomize(new Random(1));
instances.stratify(numberOfSplits);
for (int i = 0; i < numberOfSplits; i++) {
BufferedWriter bw =
new BufferedWriter(
new OutputStreamWriter(fs.create(new Path(splitsDir, "train_split_" + i + ".arff"))));
bw.write(instances.testCV(numberOfSplits, i).toString());
bw.close();
}
}
/**
* Generates the classifier.
*
* @param instances set of instances serving as training data
* @throws Exception if the classifier has not been generated successfully
*/
public void buildClassifier(Instances instances) throws Exception {
// can classifier handle the data?
getCapabilities().testWithFail(instances);
// remove instances with missing class
Instances trainData = new Instances(instances);
trainData.deleteWithMissingClass();
if (!(m_Classifier instanceof OptionHandler)) {
throw new IllegalArgumentException("Base classifier should be OptionHandler.");
}
m_InitOptions = ((OptionHandler) m_Classifier).getOptions();
m_BestPerformance = -99;
m_NumAttributes = trainData.numAttributes();
Random random = new Random(m_Seed);
trainData.randomize(random);
m_TrainFoldSize = trainData.trainCV(m_NumFolds, 0).numInstances();
// Check whether there are any parameters to optimize
if (m_CVParams.size() == 0) {
m_Classifier.buildClassifier(trainData);
m_BestClassifierOptions = m_InitOptions;
return;
}
if (trainData.classAttribute().isNominal()) {
trainData.stratify(m_NumFolds);
}
m_BestClassifierOptions = null;
// Set up m_ClassifierOptions -- take getOptions() and remove
// those being optimised.
m_ClassifierOptions = ((OptionHandler) m_Classifier).getOptions();
for (int i = 0; i < m_CVParams.size(); i++) {
Utils.getOption(((CVParameter) m_CVParams.elementAt(i)).m_ParamChar, m_ClassifierOptions);
}
findParamsByCrossValidation(0, trainData, random);
String[] options = (String[]) m_BestClassifierOptions.clone();
((OptionHandler) m_Classifier).setOptions(options);
m_Classifier.buildClassifier(trainData);
}
/**
* Cleanses the data based on misclassifications when performing cross-validation.
*
* @param data the data to train with and cleanse
* @return the cleansed data
* @throws Exception if something goes wrong
*/
private Instances cleanseCross(Instances data) throws Exception {
Instance inst;
Instances crossSet = new Instances(data);
Instances temp = new Instances(data, data.numInstances());
Instances inverseSet = new Instances(data, data.numInstances());
int count = 0;
double ans;
int iterations = 0;
int classIndex = m_classIndex;
if (classIndex < 0) {
classIndex = data.classIndex();
}
if (classIndex < 0) {
classIndex = data.numAttributes() - 1;
}
// loop until perfect
while (count != crossSet.numInstances()
&& crossSet.numInstances() >= m_numOfCrossValidationFolds) {
count = crossSet.numInstances();
// check if hit maximum number of iterations
iterations++;
if (m_numOfCleansingIterations > 0 && iterations > m_numOfCleansingIterations) {
break;
}
crossSet.setClassIndex(classIndex);
if (crossSet.classAttribute().isNominal()) {
crossSet.stratify(m_numOfCrossValidationFolds);
}
// do the folds
temp = new Instances(crossSet, crossSet.numInstances());
for (int fold = 0; fold < m_numOfCrossValidationFolds; fold++) {
Instances train = crossSet.trainCV(m_numOfCrossValidationFolds, fold);
m_cleansingClassifier.buildClassifier(train);
Instances test = crossSet.testCV(m_numOfCrossValidationFolds, fold);
// now test
for (int i = 0; i < test.numInstances(); i++) {
inst = test.instance(i);
ans = m_cleansingClassifier.classifyInstance(inst);
if (crossSet.classAttribute().isNumeric()) {
if (ans >= inst.classValue() - m_numericClassifyThreshold
&& ans <= inst.classValue() + m_numericClassifyThreshold) {
temp.add(inst);
} else if (m_invertMatching) {
inverseSet.add(inst);
}
} else { // class is nominal
if (ans == inst.classValue()) {
temp.add(inst);
} else if (m_invertMatching) {
inverseSet.add(inst);
}
}
}
}
crossSet = temp;
}
if (m_invertMatching) {
inverseSet.setClassIndex(data.classIndex());
return inverseSet;
} else {
crossSet.setClassIndex(data.classIndex());
return crossSet;
}
}
/**
* Evaluates a feature subset by cross validation
*
* @param feature_set the subset to be evaluated
* @param num_atts the number of attributes in the subset
* @return the estimated accuracy
* @throws Exception if subset can't be evaluated
*/
protected double estimatePerformance(BitSet feature_set, int num_atts) throws Exception {
m_evaluation = new Evaluation(m_theInstances);
int i;
int[] fs = new int[num_atts];
double[] instA = new double[num_atts];
int classI = m_theInstances.classIndex();
int index = 0;
for (i = 0; i < m_numAttributes; i++) {
if (feature_set.get(i)) {
fs[index++] = i;
}
}
// create new hash table
m_entries = new Hashtable((int) (m_theInstances.numInstances() * 1.5));
// insert instances into the hash table
for (i = 0; i < m_numInstances; i++) {
Instance inst = m_theInstances.instance(i);
for (int j = 0; j < fs.length; j++) {
if (fs[j] == classI) {
instA[j] = Double.MAX_VALUE; // missing for the class
} else if (inst.isMissing(fs[j])) {
instA[j] = Double.MAX_VALUE;
} else {
instA[j] = inst.value(fs[j]);
}
}
insertIntoTable(inst, instA);
}
if (m_CVFolds == 1) {
// calculate leave one out error
for (i = 0; i < m_numInstances; i++) {
Instance inst = m_theInstances.instance(i);
for (int j = 0; j < fs.length; j++) {
if (fs[j] == classI) {
instA[j] = Double.MAX_VALUE; // missing for the class
} else if (inst.isMissing(fs[j])) {
instA[j] = Double.MAX_VALUE;
} else {
instA[j] = inst.value(fs[j]);
}
}
evaluateInstanceLeaveOneOut(inst, instA);
}
} else {
m_theInstances.randomize(m_rr);
m_theInstances.stratify(m_CVFolds);
// calculate 10 fold cross validation error
for (i = 0; i < m_CVFolds; i++) {
Instances insts = m_theInstances.testCV(m_CVFolds, i);
evaluateFoldCV(insts, fs);
}
}
switch (m_evaluationMeasure) {
case EVAL_DEFAULT:
if (m_classIsNominal) {
return m_evaluation.pctCorrect();
}
return -m_evaluation.rootMeanSquaredError();
case EVAL_ACCURACY:
return m_evaluation.pctCorrect();
case EVAL_RMSE:
return -m_evaluation.rootMeanSquaredError();
case EVAL_MAE:
return -m_evaluation.meanAbsoluteError();
case EVAL_AUC:
double[] classPriors = m_evaluation.getClassPriors();
Utils.normalize(classPriors);
double weightedAUC = 0;
for (i = 0; i < m_theInstances.classAttribute().numValues(); i++) {
double tempAUC = m_evaluation.areaUnderROC(i);
if (!Utils.isMissingValue(tempAUC)) {
weightedAUC += (classPriors[i] * tempAUC);
} else {
System.err.println("Undefined AUC!!");
}
}
return weightedAUC;
}
// shouldn't get here
return 0.0;
}
