ADD: recall measurement

src/mhtree/MHTree.java

@@ -11,7 +11,6 @@ import messif.operations.data.InsertOperation;
 import messif.operations.query.ApproxKNNQueryOperation;
 import messif.operations.query.KNNQueryOperation;
 import messif.statistics.StatisticCounter;
-import mhtree.benchmarking.Utils;
 
 import java.io.Serializable;
 import java.util.*;

src/mhtree/Utils.java

+package mhtree;
+
+import messif.objects.util.DistanceRankedObject;
+import messif.objects.util.RankedAbstractObject;
+import messif.operations.query.ApproxKNNQueryOperation;
+import messif.operations.query.KNNQueryOperation;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+public class Utils {
+
+    // comparing done based on distances, counts how many of the same distances of KNNQueryOperation were presents in the answer of ApproxKNNQueryOperation
+    public static double measureRecall(ApproxKNNQueryOperation approxKNNQueryOperation, KNNQueryOperation knnQueryOperation) {
+        if (approxKNNQueryOperation.getAnswerCount() == 0) return 0d;
+        if (knnQueryOperation.getAnswerCount() == 0) return -1d;
+
+        List<RankedAbstractObject> objects = new ArrayList<>(knnQueryOperation.getAnswerCount());
+        for (RankedAbstractObject object : knnQueryOperation)
+            objects.add(object);
+
+        Map<Float, Long> frequencyMap = objects.parallelStream()
+                .map(DistanceRankedObject::getDistance)
+                .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
+
+        long trueCount = 0;
+
+        for (RankedAbstractObject approxObject : approxKNNQueryOperation) {
+            float distance = approxObject.getDistance();
+            if (frequencyMap.containsKey(distance)) {
+                long count = frequencyMap.get(distance);
+                if (count == 1) {
+                    frequencyMap.remove(distance);
+                } else {
+                    frequencyMap.replace(distance, count - 1);
+                }
+                trueCount++;
+            }
+        }
+
+        return trueCount / (double) knnQueryOperation.getAnswerCount();
+    }
+}