/**
* Preprocessing step: determine the radii of interest for each point.
*
* @param ids IDs to process
* @param rangeQuery Range query
* @param interestingDistances Distances of interest
*/
protected void precomputeInterestingRadii(
DBIDs ids,
RangeQuery<O> rangeQuery,
WritableDataStore<DoubleIntArrayList> interestingDistances) {
FiniteProgress progressPreproc =
LOG.isVerbose() ? new FiniteProgress("LOCI preprocessing", ids.size(), LOG) : null;
for (DBIDIter iditer = ids.iter(); iditer.valid(); iditer.advance()) {
DoubleDBIDList neighbors = rangeQuery.getRangeForDBID(iditer, rmax);
// build list of critical distances
DoubleIntArrayList cdist = new DoubleIntArrayList(neighbors.size() << 1);
{
int i = 0;
DoubleDBIDListIter ni = neighbors.iter();
while (ni.valid()) {
final double curdist = ni.doubleValue();
++i;
ni.advance();
// Skip, if tied to the next object:
if (ni.valid() && curdist == ni.doubleValue()) {
continue;
}
cdist.append(curdist, i);
// Scale radius, and reinsert
if (alpha != 1.) {
final double ri = curdist / alpha;
if (ri <= rmax) {
cdist.append(ri, Integer.MIN_VALUE);
}
}
}
}
cdist.sort();
// fill the gaps to have fast lookups of number of neighbors at a given
// distance.
int lastk = 0;
for (int i = 0, size = cdist.size(); i < size; i++) {
final int k = cdist.getInt(i);
if (k == Integer.MIN_VALUE) {
cdist.setValue(i, lastk);
} else {
lastk = k;
}
}
// TODO: shrink the list, removing duplicate radii?
interestingDistances.put(iditer, cdist);
LOG.incrementProcessed(progressPreproc);
}
LOG.ensureCompleted(progressPreproc);
}
/**
* Run the algorithm
*
* @param database Database to process
* @param relation Relation to process
* @return Outlier result
*/
public OutlierResult run(Database database, Relation<O> relation) {
DistanceQuery<O> distFunc = database.getDistanceQuery(relation, getDistanceFunction());
RangeQuery<O> rangeQuery = database.getRangeQuery(distFunc);
DBIDs ids = relation.getDBIDs();
// LOCI preprocessing step
WritableDataStore<DoubleIntArrayList> interestingDistances =
DataStoreUtil.makeStorage(
relation.getDBIDs(),
DataStoreFactory.HINT_TEMP | DataStoreFactory.HINT_SORTED,
DoubleIntArrayList.class);
precomputeInterestingRadii(ids, rangeQuery, interestingDistances);
// LOCI main step
FiniteProgress progressLOCI =
LOG.isVerbose() ? new FiniteProgress("LOCI scores", relation.size(), LOG) : null;
WritableDoubleDataStore mdef_norm =
DataStoreUtil.makeDoubleStorage(relation.getDBIDs(), DataStoreFactory.HINT_STATIC);
WritableDoubleDataStore mdef_radius =
DataStoreUtil.makeDoubleStorage(relation.getDBIDs(), DataStoreFactory.HINT_STATIC);
DoubleMinMax minmax = new DoubleMinMax();
// Shared instance, to save allocations.
MeanVariance mv_n_r_alpha = new MeanVariance();
for (DBIDIter iditer = ids.iter(); iditer.valid(); iditer.advance()) {
final DoubleIntArrayList cdist = interestingDistances.get(iditer);
final double maxdist = cdist.getDouble(cdist.size() - 1);
final int maxneig = cdist.getInt(cdist.size() - 1);
double maxmdefnorm = 0.0;
double maxnormr = 0;
if (maxneig >= nmin) {
// Compute the largest neighborhood we will need.
DoubleDBIDList maxneighbors = rangeQuery.getRangeForDBID(iditer, maxdist);
// TODO: Ensure the result is sorted. This is currently implied.
// For any critical distance, compute the normalized MDEF score.
for (int i = 0, size = cdist.size(); i < size; i++) {
// Only start when minimum size is fulfilled
if (cdist.getInt(i) < nmin) {
continue;
}
final double r = cdist.getDouble(i);
final double alpha_r = alpha * r;
// compute n(p_i, \alpha * r) from list (note: alpha_r is not cdist!)
final int n_alphar = cdist.getInt(cdist.find(alpha_r));
// compute \hat{n}(p_i, r, \alpha) and the corresponding \simga_{MDEF}
mv_n_r_alpha.reset();
for (DoubleDBIDListIter neighbor = maxneighbors.iter();
neighbor.valid();
neighbor.advance()) {
// Stop at radius r
if (neighbor.doubleValue() > r) {
break;
}
DoubleIntArrayList cdist2 = interestingDistances.get(neighbor);
int rn_alphar = cdist2.getInt(cdist2.find(alpha_r));
mv_n_r_alpha.put(rn_alphar);
}
// We only use the average and standard deviation
final double nhat_r_alpha = mv_n_r_alpha.getMean();
final double sigma_nhat_r_alpha = mv_n_r_alpha.getNaiveStddev();
// Redundant divisions by nhat_r_alpha removed.
final double mdef = nhat_r_alpha - n_alphar;
final double sigmamdef = sigma_nhat_r_alpha;
final double mdefnorm = mdef / sigmamdef;
if (mdefnorm > maxmdefnorm) {
maxmdefnorm = mdefnorm;
maxnormr = r;
}
}
} else {
// FIXME: when nmin was not fulfilled - what is the proper value then?
maxmdefnorm = Double.POSITIVE_INFINITY;
maxnormr = maxdist;
}
mdef_norm.putDouble(iditer, maxmdefnorm);
mdef_radius.putDouble(iditer, maxnormr);
minmax.put(maxmdefnorm);
LOG.incrementProcessed(progressLOCI);
}
LOG.ensureCompleted(progressLOCI);
DoubleRelation scoreResult =
new MaterializedDoubleRelation(
"LOCI normalized MDEF", "loci-mdef-outlier", mdef_norm, relation.getDBIDs());
OutlierScoreMeta scoreMeta =
new QuotientOutlierScoreMeta(
minmax.getMin(), minmax.getMax(), 0.0, Double.POSITIVE_INFINITY, 0.0);
OutlierResult result = new OutlierResult(scoreMeta, scoreResult);
result.addChildResult(
new MaterializedDoubleRelation(
"LOCI MDEF Radius", "loci-critical-radius", mdef_radius, relation.getDBIDs()));
return result;
}
