/**
* 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);
}
