Amol Singh created MATH-1367:
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Summary: DBSCAN Implementation does not count the seed point
itself as part of its neighbors count
Key: MATH-1367
URL: https://issues.apache.org/jira/browse/MATH-1367
Project: Commons Math
Issue Type: Bug
Affects Versions: 3.6.1
Reporter: Amol Singh
Fix For: 4.0
The DSCAN paper describes the eps-neighborhood of a point as
https://www.aaai.org/Papers/KDD/1996/KDD96-037.pdf (Page 2)
Definition 1: (Eps-neighborhood of a point) The Eps-neighborhood of a point p,
denoted by NEps(p), is defined by NEps(p) = {q ∈ D | dist(p,q)< Eps}.
in other words for all q points that are a member of database D whose distance
from p is less that Eps should be classified as a neighbor. This should include
the point itself.
The implementation however has a reference check to the point itself and does
not add it to its neighbors list.
private List<T> getNeighbors(final T point, final Collection<T> points) {
final List<T> neighbors = new ArrayList<T>();
for (final T neighbor : points) {
if (point != neighbor && distance(neighbor, point) <= eps) {
neighbors.add(neighbor);
}
}
return neighbors;
}
point != neighbor check should be removed here. The cluster should contain the
point itself in it. Keeping this check effectively is raising the minPts count
by 1.
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