Attic

Code or methods that've been tried and rejected.

DBSCAN Clustering with ELKI

• Produces correct clusters.
• Failed under concurrent use.
• Requires excessive object creation.

/**
 * Applies the <a href="http://en.wikipedia.org/wiki/DBSCAN">DBSCAN</a> clustering algorithm to the given points.
 *
 * @param points Points to cluster (_D_).
 * @param ε Threshold distance.
 * @param size Minimum cluster size (_MinPts_).
 *
 * @param ev Operations on numeric values.
 *
 * @tparam T Point measurement.
 */
def clusters[T](points: Seq[Point[T]], ε: T, size: Int)(implicit ev: Numeric[T]): Set[Set[Point[T]]] = {
  LoggingConfiguration.setStatistics()

  val matrix = points.map(p => Array(ev.toDouble(p.x), ev.toDouble(p.y))).toArray[Array[Double]]
  val conn = new ArrayAdapterDatabaseConnection(matrix)
  val db = new StaticArrayDatabase(conn, null)
  db.initialize()

  val relations: Relation[DoubleVector] = db.getRelation(TypeUtil.DOUBLE_VECTOR_FIELD)

  val params = new ListParameterization
  params.addParameter(DBSCAN.Parameterizer.EPSILON_ID, ε)
  params.addParameter(DBSCAN.Parameterizer.MINPTS_ID, size)
  val clustering: DBSCAN[DoubleDistance, _] = ClassGenericsUtil.parameterizeOrAbort(classOf[DBSCAN[_, _]], params)

  val results = ResultUtil.getClusteringResults(clustering.run(db))

  /* Accumulator for clusters. */
  val clusters = mutable.ArrayBuffer.empty[Seq[Point[T]]]

  for (r <- results) {
    for (c <- r.getAllClusters) {
      /* Accumulator for clustered points. */
      val cluster = mutable.ArrayBuffer.empty[Point[T]]

      val i = c.getIDs.iter()
      while (i.valid()) {
        val datum = relations.get(i)
        val index = DBIDUtil.asInteger(i) - 1

        val point = points(index)

        /* Guard against possible API changes where the database index doesn't match with the input sequence index. */
        assert(datum.doubleValue(0) == ev.toDouble(point.x) && datum.doubleValue(1) == ev.toDouble(point.y), "Related datum for index $index does not match the expected point from the source values (expected $datum, got $point).")

        cluster += point
        i.advance()
      }

      clusters += cluster.toSeq
    }
  }

  clusters.map(_.toSet).toSet.filter(_.nonEmpty)
}