/// <summary>
/// Performs the DBSCAN clustering algorithm.
/// </summary>
/// <param name="allPoints">Dataset</param>
/// <param name="epsilon">Desired region ball radius</param>
/// <param name="minPts">Minimum number of points to be in a region</param>
/// <param name="clusters">returns sets of clusters, renew the parameter</param>
public void ComputeClusterDbscan(T[] allPoints, double epsilon, int minPts, out HashSet <T[]> clusters)
{
DbscanPoint <T>[] allPointsDbscan = allPoints.Select(x => new DbscanPoint <T>(x)).ToArray();
int clusterId = 0;
for (int i = 0; i < allPointsDbscan.Length; i++)
{
DbscanPoint <T> p = allPointsDbscan[i];
if (p.IsVisited)
{
continue;
}
p.IsVisited = true;
DbscanPoint <T>[] neighborPts = null;
RegionQuery(allPointsDbscan, p.ClusterPoint, epsilon, out neighborPts);
if (neighborPts.Length < minPts)
{
p.ClusterId = (int)ClusterIds.Noise;
}
else
{
clusterId++;
ExpandCluster(allPointsDbscan, p, neighborPts, clusterId, epsilon, minPts);
}
}
clusters = new HashSet <T[]>(
allPointsDbscan
.Where(x => x.ClusterId > 0)
.GroupBy(x => x.ClusterId)
.Select(x => x.Select(y => y.ClusterPoint).ToArray())
);
}
/// <summary>
///
/// </summary>
/// <param name="allPoints">Dataset</param>
/// <param name="point">point to be in a cluster</param>
/// <param name="neighborPts">other points in same region with point parameter</param>
/// <param name="clusterId">given clusterId</param>
/// <param name="epsilon">Desired region ball range</param>
/// <param name="minPts">Minimum number of points to be in a region</param>
private void ExpandCluster(DbscanPoint <T>[] allPoints, DbscanPoint <T> point, DbscanPoint <T>[] neighborPts, int clusterId, double epsilon, int minPts)
{
point.ClusterId = clusterId;
for (int i = 0; i < neighborPts.Length; i++)
{
DbscanPoint <T> pn = neighborPts[i];
if (!pn.IsVisited)
{
pn.IsVisited = true;
DbscanPoint <T>[] neighborPts2 = null;
RegionQuery(allPoints, pn.ClusterPoint, epsilon, out neighborPts2);
if (neighborPts2.Length >= minPts)
{
neighborPts = neighborPts.Union(neighborPts2).ToArray();
}
}
if (pn.ClusterId == (int)ClusterIds.Unclassified)
{
pn.ClusterId = clusterId;
}
}
}