1 files changed, 62 insertions, 0 deletions

diff --git a/subprojects/viatra-runtime/src/main/java/tools/refinery/viatra/runtime/matchers/planning/helpers/StatisticsHelper.java b/subprojects/viatra-runtime/src/main/java/tools/refinery/viatra/runtime/matchers/planning/helpers/StatisticsHelper.java
new file mode 100644
index 00000000..b4f848a7
--- /dev/null
+++ b/subprojects/viatra-runtime/src/main/java/tools/refinery/viatra/runtime/matchers/planning/helpers/StatisticsHelper.java
@@ -0,0 +1,62 @@
+/*******************************************************************************
+ * Copyright (c) 2010-2018, Gabor Bergmann, IncQuery Labs Ltd.
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-v20.html.
+ * 
+ * SPDX-License-Identifier: EPL-2.0
+ *******************************************************************************/
+package tools.refinery.viatra.runtime.matchers.planning.helpers;
+
+import java.util.Optional;
+import java.util.function.BiFunction;
+
+import tools.refinery.viatra.runtime.matchers.tuple.TupleMask;
+import tools.refinery.viatra.runtime.matchers.util.Accuracy;
+
+/**
+ * Helpers dealing with optionally present statistics information 
+ * 
+ * @author Gabor Bergmann
+ * @since 2.1
+ *
+ */
+public class StatisticsHelper {
+    
+    private StatisticsHelper() {
+        // Hidden utility class constructor
+    }
+    
+    public static Optional<Double> estimateAverageBucketSize(TupleMask groupMask, Accuracy requiredAccuracy, 
+            BiFunction<TupleMask, Accuracy, Optional<Long>> estimateCardinality) 
+    {
+        if (groupMask.isIdentity()) return Optional.of(1.0);
+        
+        Accuracy numeratorAccuracy = requiredAccuracy;
+        Accuracy denominatorAccuracy = requiredAccuracy.reciprocal();
+        TupleMask identityMask = TupleMask.identity(groupMask.sourceWidth);
+        
+        Optional<Long> totalCountEstimate  = estimateCardinality.apply(identityMask, numeratorAccuracy);
+        Optional<Long> bucketCountEstimate = estimateCardinality.apply(groupMask,    denominatorAccuracy);
+
+        return totalCountEstimate.flatMap(matchCount -> 
+            bucketCountEstimate.map(bucketCount -> 
+                bucketCount == 0L ? 0L : ((double) matchCount) / bucketCount
+        ));
+    }
+
+    public static Optional<Double> min(Optional<Double> a,  Optional<Double> b) {
+        if (b.isPresent()) {
+            if (a.isPresent()) {
+                return Optional.of(Math.min(a.get(), b.get()));
+            } else return b;
+        } else return a;
+    }
+    public static Optional<Double> min(Optional<Double> a, double b) {
+        if (a.isPresent()) {
+            return Optional.of(Math.min(a.get(), b));
+        } else return Optional.of(b);
+    }
+
+
+}