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diff --git a/src/de/lmu/ifi/dbs/elki/evaluation/index/IndexPurity.java b/src/de/lmu/ifi/dbs/elki/evaluation/index/IndexPurity.java
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+package de.lmu.ifi.dbs.elki.evaluation.index;
+
+/*
+ This file is part of ELKI:
+ Environment for Developing KDD-Applications Supported by Index-Structures
+
+ Copyright (C) 2012
+ Ludwig-Maximilians-Universität München
+ Lehr- und Forschungseinheit für Datenbanksysteme
+ ELKI Development Team
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU Affero General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ GNU Affero General Public License for more details.
+
+ You should have received a copy of the GNU Affero General Public License
+ along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map.Entry;
+
+import de.lmu.ifi.dbs.elki.data.DoubleVector;
+import de.lmu.ifi.dbs.elki.database.Database;
+import de.lmu.ifi.dbs.elki.database.ids.DBID;
+import de.lmu.ifi.dbs.elki.database.relation.Relation;
+import de.lmu.ifi.dbs.elki.evaluation.Evaluator;
+import de.lmu.ifi.dbs.elki.index.tree.Node;
+import de.lmu.ifi.dbs.elki.index.tree.spatial.SpatialDirectoryEntry;
+import de.lmu.ifi.dbs.elki.index.tree.spatial.SpatialEntry;
+import de.lmu.ifi.dbs.elki.index.tree.spatial.SpatialIndexTree;
+import de.lmu.ifi.dbs.elki.index.tree.spatial.SpatialPointLeafEntry;
+import de.lmu.ifi.dbs.elki.math.MeanVariance;
+import de.lmu.ifi.dbs.elki.result.CollectionResult;
+import de.lmu.ifi.dbs.elki.result.HierarchicalResult;
+import de.lmu.ifi.dbs.elki.result.Result;
+import de.lmu.ifi.dbs.elki.result.ResultUtil;
+import de.lmu.ifi.dbs.elki.utilities.DatabaseUtil;
+
+/**
+ * Compute the purity of index pages as a naive measure for performance
+ * capabilities using the Gini index.
+ * 
+ * @author Erich Schubert
+ */
+public class IndexPurity implements Evaluator {
+  /**
+   * Constructor.
+   */
+  public IndexPurity() {
+    super();
+  }
+
+  @Override
+  public void processNewResult(HierarchicalResult baseResult, Result newResult) {
+    Database database = ResultUtil.findDatabase(baseResult);
+    final ArrayList<SpatialIndexTree<?, ?>> indexes = ResultUtil.filterResults(newResult, SpatialIndexTree.class);
+    if(indexes == null || indexes.size() <= 0) {
+      return;
+    }
+    Relation<String> lblrel = DatabaseUtil.guessLabelRepresentation(database);
+    for(SpatialIndexTree<?, ?> index : indexes) {
+      List<? extends SpatialEntry> leaves = index.getLeaves();
+      MeanVariance mv = new MeanVariance();
+      for(SpatialEntry e : leaves) {
+        SpatialDirectoryEntry leaf = (SpatialDirectoryEntry) e;
+        Node<?> n = index.getNode(leaf.getEntryID());
+
+        final int total = n.getNumEntries();
+        HashMap<String, Integer> map = new HashMap<String, Integer>(total);
+        for(int i = 0; i < total; i++) {
+          DBID id = ((SpatialPointLeafEntry) n.getEntry(i)).getDBID();
+          String label = lblrel.get(id);
+          Integer val = map.get(label);
+          if(val == null) {
+            val = 1;
+          }
+          else {
+            val += 1;
+          }
+          map.put(label, val);
+        }
+        double gini = 0.0;
+        for(Entry<String, Integer> ent : map.entrySet()) {
+          double rel = ent.getValue() / (double) total;
+          gini += rel * rel;
+        }
+        mv.put(gini);
+      }
+      Collection<DoubleVector> col = new java.util.Vector<DoubleVector>();
+      col.add(new DoubleVector(new double[] { mv.getMean(), mv.getSampleStddev() }));
+      database.getHierarchy().add((Result) index, new CollectionResult<DoubleVector>("Gini coefficient of index", "index-gini", col));
+    }
+  }
+}