private double getGiniIndex(ClassificationCounter cc) {
double sum = 0.0d;
for (Map.Entry<Serializable, Double> e : cc.getCounts().entrySet()) {
double error = (cc.getTotal() > 0) ? e.getValue() / cc.getTotal() : 0;
sum += error * error;
}
return 1.0d - sum;
}
@Override
public double scoreSplit(ClassificationCounter a, ClassificationCounter b) {
ClassificationCounter parent = ClassificationCounter.merge(a, b);
double parentGiniIndex = getGiniIndex(parent);
double aGiniIndex = getGiniIndex(a) * a.getTotal() / parent.getTotal();
double bGiniIndex = getGiniIndex(b) * b.getTotal() / parent.getTotal();
return parentGiniIndex - aGiniIndex - bGiniIndex;
}