/**
* Discretizes an attribute using bins.
*
* @param instances the dataset to discretize.
* @param attIndex the attribute index.
* @param bins the bins.
*/
public static void discretize(Instances instances, int attIndex, Bins bins) {
Attribute attribute = instances.getAttributes().get(attIndex);
BinnedAttribute binnedAttribute = new BinnedAttribute(attribute.getName(), bins);
binnedAttribute.setIndex(attribute.getIndex());
instances.getAttributes().set(attIndex, binnedAttribute);
for (Instance instance : instances) {
int v = bins.getIndex(instance.getValue(attribute.getIndex()));
instance.setValue(attribute.getIndex(), v);
}
}
/**
* Compute bins for a specified attribute.
*
* @param instances the dataset to discretize.
* @param attIndex the attribute index.
* @param maxNumBins the number of bins.
*/
public static Bins computeBins(Instances instances, int attIndex, int maxNumBins) {
Attribute attribute = instances.getAttributes().get(attIndex);
List<Element<Double>> list = new ArrayList<>();
for (Instance instance : instances) {
list.add(new Element<Double>(instance.getWeight(), instance.getValue(attribute)));
}
Collections.sort(list);
List<DoublePair> stats = new ArrayList<>();
getStats(list, stats);
Bins bins = new Bins();
if (stats.size() <= maxNumBins) {
double[] a = new double[stats.size()];
for (int i = 0; i < a.length; i++) {
a[i] = stats.get(i).v1;
}
bins.boundaries = bins.medians = a;
} else {
double totalWeight = 0;
for (DoublePair stat : stats) {
totalWeight += stat.v2;
}
double binSize = totalWeight / maxNumBins;
List<Double> boundaryList = new ArrayList<>();
List<Double> medianList = new ArrayList<>();
int start = 0;
double weight = 0;
for (int i = 0; i < stats.size(); i++) {
weight += stats.get(i).v2;
totalWeight -= stats.get(i).v2;
if (weight >= binSize) {
if (i == start) {
boundaryList.add(stats.get(start).v1);
medianList.add(stats.get(start).v1);
weight = 0;
start = i + 1;
} else {
double d1 = weight - binSize;
double d2 = stats.get(i).v2 - d1;
if (d1 < d2) {
boundaryList.add(stats.get(i).v1);
medianList.add(getMedian(stats, start, weight / 2));
start = i + 1;
weight = 0;
} else {
weight -= stats.get(i).v2;
boundaryList.add(stats.get(i - 1).v1);
medianList.add(getMedian(stats, start, weight / 2));
start = i;
weight = stats.get(i).v2;
}
}
binSize = (totalWeight + weight) / (maxNumBins - boundaryList.size());
} else if (i == stats.size() - 1) {
boundaryList.add(stats.get(i).v1);
medianList.add(getMedian(stats, start, weight / 2));
}
}
bins.boundaries = new double[boundaryList.size()];
bins.medians = new double[medianList.size()];
for (int i = 0; i < bins.boundaries.length; i++) {
bins.boundaries[i] = boundaryList.get(i);
bins.medians[i] = medianList.get(i);
}
}
return bins;
}
