/**
* Runs the DBSCAN algorithm on the specified partition of the database in the given subspace. If
* parameter {@code ids} is null DBSCAN will be applied to the whole database.
*
* @param relation the database holding the objects to run DBSCAN on
* @param ids the IDs of the database defining the partition to run DBSCAN on - if this parameter
* is null DBSCAN will be applied to the whole database
* @param subspace the subspace to run DBSCAN on
* @return the clustering result of the DBSCAN run
*/
private List<Cluster<Model>> runDBSCAN(Relation<V> relation, DBIDs ids, Subspace subspace) {
// distance function
distanceFunction.setSelectedDimensions(subspace.getDimensions());
ProxyDatabase proxy;
if (ids == null) {
// TODO: in this case, we might want to use an index - the proxy below
// will prevent this!
ids = relation.getDBIDs();
}
proxy = new ProxyDatabase(ids, relation);
DBSCAN<V> dbscan = new DBSCAN<>(distanceFunction, epsilon, minpts);
// run DBSCAN
if (LOG.isVerbose()) {
LOG.verbose("\nRun DBSCAN on subspace " + subspace.dimensonsToString());
}
Clustering<Model> dbsres = dbscan.run(proxy);
// separate cluster and noise
List<Cluster<Model>> clusterAndNoise = dbsres.getAllClusters();
List<Cluster<Model>> clusters = new ArrayList<>();
for (Cluster<Model> c : clusterAndNoise) {
if (!c.isNoise()) {
clusters.add(c);
}
}
return clusters;
}
/**
* Returns the list of all {@code (d-1)}-dimensional subspaces of the specified {@code
* d}-dimensional subspace.
*
* @param subspace the {@code d}-dimensional subspace
* @return a list of all {@code (d-1)}-dimensional subspaces
*/
private List<Subspace> lowerSubspaces(Subspace subspace) {
int dimensionality = subspace.dimensionality();
if (dimensionality <= 1) {
return null;
}
// order result according to the dimensions
List<Subspace> result = new ArrayList<>();
long[] dimensions = subspace.getDimensions();
for (int dim = BitsUtil.nextSetBit(dimensions, 0);
dim >= 0;
dim = BitsUtil.nextSetBit(dimensions, dim + 1)) {
long[] newDimensions = dimensions.clone();
BitsUtil.clearI(newDimensions, dim);
result.add(new Subspace(newDimensions));
}
return result;
}
