From 4ca264ed3b56fcfa6e6ef34e241a13e8790497c2 Mon Sep 17 00:00:00 2001
From: Alexandre <alexandre.perles@gmail.com>
Date: Wed, 16 Aug 2023 16:47:54 +0200
Subject: [PATCH] Add CalinskiHarabazIndex
---
.../amas4dc/cluster/CalinskiHarabazIndex.java | 59 +++++++++++++++++++
1 file changed, 59 insertions(+)
create mode 100644 src/main/java/fr/irit/smac/amas4dc/cluster/CalinskiHarabazIndex.java
diff --git a/src/main/java/fr/irit/smac/amas4dc/cluster/CalinskiHarabazIndex.java b/src/main/java/fr/irit/smac/amas4dc/cluster/CalinskiHarabazIndex.java
new file mode 100644
index 0000000..dc343f9
--- /dev/null
+++ b/src/main/java/fr/irit/smac/amas4dc/cluster/CalinskiHarabazIndex.java
@@ -0,0 +1,59 @@
+package fr.irit.smac.amas4dc.cluster;
+
+import fr.irit.smac.amas4dc.amas.MASSettings;
+
+import java.util.List;
+
+public class CalinskiHarabazIndex<T extends DataPoint> {
+
+ public double compute(MASSettings<T> masSettings, List<ExtendedCluster<T>> clusters) {
+ var ssb = computeBetweenClusterVariance(clusters, masSettings);
+ var ssw = computeWithinClusterVariance(clusters, masSettings);
+
+ if (ssw == 0) {
+ // Avoid division by zero
+ return Double.POSITIVE_INFINITY;
+ }
+
+ return ssb / ssw;
+ }
+
+ private double computeBetweenClusterVariance(List<ExtendedCluster<T>> clusters, MASSettings<T> masSettings) {
+ var centroid = computeGlobalCentroid(clusters, masSettings);
+ var ssb = 0.0;
+
+ for (var cluster : clusters) {
+ var centroidDist = 1.0/masSettings.similarityScoreMethod().apply(cluster.getRepresentative(), centroid);
+ ssb += centroidDist * centroidDist * cluster.getContent().size();
+ }
+
+ return ssb;
+ }
+
+ private double computeWithinClusterVariance(List<ExtendedCluster<T>> clusters, MASSettings<T> masSettings) {
+ var ssw = 0.0;
+
+ for (var cluster : clusters) {
+ var clusterCentroid = cluster.getRepresentative();
+ var clusterSumDist = 0.0;
+
+ for (var point : cluster.getContent()) {
+ var dist = 1.0/masSettings.similarityScoreMethod().apply(point, clusterCentroid);
+ clusterSumDist += dist * dist;
+ }
+
+ ssw += clusterSumDist;
+ }
+
+ return ssw;
+ }
+
+ private T computeGlobalCentroid(List<ExtendedCluster<T>> clusters, MASSettings<T> masSettings) {
+ var fused = clusters.get(0).getRepresentative();
+ for (int i = 1; i < clusters.size(); i++) {
+ fused = masSettings.dataPointFuser().apply(fused, clusters.get(i).getRepresentative());
+ }
+ return fused;
+ }
+}
+
--
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