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diff --git a/src/de/lmu/ifi/dbs/elki/evaluation/scores/PrecisionAtKEvaluation.java b/src/de/lmu/ifi/dbs/elki/evaluation/scores/PrecisionAtKEvaluation.java
new file mode 100644
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+++ b/src/de/lmu/ifi/dbs/elki/evaluation/scores/PrecisionAtKEvaluation.java
@@ -0,0 +1,127 @@
+package de.lmu.ifi.dbs.elki.evaluation.scores;
+/*
+ This file is part of ELKI:
+ Environment for Developing KDD-Applications Supported by Index-Structures
+
+ Copyright (C) 2014
+ 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 de.lmu.ifi.dbs.elki.utilities.optionhandling.AbstractParameterizer;
+import de.lmu.ifi.dbs.elki.utilities.optionhandling.OptionID;
+import de.lmu.ifi.dbs.elki.utilities.optionhandling.constraints.CommonConstraints;
+import de.lmu.ifi.dbs.elki.utilities.optionhandling.parameterization.Parameterization;
+import de.lmu.ifi.dbs.elki.utilities.optionhandling.parameters.IntParameter;
+
+/**
+ * Evaluate using Precision@k, or R-precision (when {@code k=0}).
+ * 
+ * When {@code k=0}, then it is set to the number of positive objects, and the
+ * returned value is the R-precision, or the precision-recall break-even-point
+ * (BEP).
+ *
+ * @author Erich Schubert
+ */
+public class PrecisionAtKEvaluation extends AbstractScoreEvaluation {
+  /**
+   * Static instance
+   */
+  public static final PrecisionAtKEvaluation RPRECISION = new PrecisionAtKEvaluation(0);
+
+  /**
+   * Parameter k.
+   */
+  int k;
+
+  /**
+   * Constructor.
+   *
+   * @param k k to evaluate at. May be 0.
+   */
+  public PrecisionAtKEvaluation(int k) {
+    this.k = k;
+  }
+
+  @Override
+  public <I extends ScoreIter> double evaluate(Predicate<? super I> predicate, I iter) {
+    final int k = (this.k > 0) ? this.k : predicate.numPositive();
+    int total = 0;
+    double score = 0.;
+    while(iter.valid() && total < k) {
+      int posthis = 0, cntthis = 0;
+      // positive or negative match?
+      do {
+        if(predicate.test(iter)) {
+          ++posthis;
+        }
+        ++cntthis;
+        iter.advance();
+      } // Loop while tied:
+      while(iter.valid() && iter.tiedToPrevious());
+      // Special tie computations only when we reach k.
+      if(total + cntthis > k) {
+        // p = posthis / cntthis chance of being positive
+        // n = (k-total) draws.
+        // expected value = n * p
+        score += posthis / (double) cntthis * (k - total);
+        total = k;
+        break;
+      }
+      score += posthis;
+      total += cntthis;
+    }
+    return score / total;
+  }
+
+  /**
+   * Parameterization class.
+   * 
+   * @author Erich Schubert
+   *
+   * @apiviz.exclude
+   */
+  public static class Parameterizer extends AbstractParameterizer {
+    /**
+     * Option ID for the k parameter.
+     */
+    public static final OptionID K_ID = new OptionID("precision.k", //
+    "k value for precision@k. Can be set to 0, to get R-precision, or the precision-recall-break-even-point.");
+
+    /**
+     * K parameter
+     */
+    int k;
+
+    @Override
+    protected void makeOptions(Parameterization config) {
+      super.makeOptions(config);
+
+      IntParameter kP = new IntParameter(K_ID) //
+      .setDefaultValue(0) //
+      .addConstraint(CommonConstraints.GREATER_EQUAL_ZERO_INT);
+      if(config.grab(kP)) {
+        k = kP.intValue();
+      }
+    }
+
+    @Override
+    protected PrecisionAtKEvaluation makeInstance() {
+      return k > 0 ? new PrecisionAtKEvaluation(k) : RPRECISION;
+    }
+  }
+}