1 files changed, 82 insertions, 0 deletions

diff --git a/subprojects/viatra-runtime/src/main/java/tools/refinery/viatra/runtime/matchers/aggregators/LongAverageOperator.java b/subprojects/viatra-runtime/src/main/java/tools/refinery/viatra/runtime/matchers/aggregators/LongAverageOperator.java
new file mode 100644
index 00000000..d56c9507
--- /dev/null
+++ b/subprojects/viatra-runtime/src/main/java/tools/refinery/viatra/runtime/matchers/aggregators/LongAverageOperator.java
@@ -0,0 +1,82 @@
+/*******************************************************************************
+ * Copyright (c) 2010-2018, Zoltan Ujhelyi, 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.aggregators;
+
+import java.util.OptionalDouble;
+import java.util.stream.Stream;
+
+import tools.refinery.viatra.runtime.matchers.psystem.aggregations.IMultisetAggregationOperator;
+
+/**
+ * @author Zoltan Ujhelyi
+ * @since 2.0
+ */
+public class LongAverageOperator implements IMultisetAggregationOperator<Long, AverageAccumulator<Long>, Double> {
+
+    public static final LongAverageOperator INSTANCE = new LongAverageOperator();
+    
+    private LongAverageOperator() {
+        // Singleton, do not call.
+    }
+    
+    @Override
+    public String getShortDescription() {
+        return "avg<Integer> incrementally computes the average of java.lang.Integer values";
+    }
+
+    @Override
+    public String getName() {
+        return "avg<Integer>";
+    }
+
+    @Override
+    public AverageAccumulator<Long> createNeutral() {
+        return new AverageAccumulator<Long>(0l, 0l);
+    }
+
+    @Override
+    public boolean isNeutral(AverageAccumulator<Long> result) {
+        return result.count == 0l;
+    }
+
+    @Override
+    public AverageAccumulator<Long> update(AverageAccumulator<Long> oldResult, Long updateValue,
+            boolean isInsertion) {
+        if (isInsertion) {
+            oldResult.value += updateValue;
+            oldResult.count++;
+        } else {
+            oldResult.value -= updateValue;
+            oldResult.count--;
+        }
+        return oldResult;
+    }
+
+    @Override
+    public Double getAggregate(AverageAccumulator<Long> result) {
+        return (result.count == 0)
+                ? null
+                : ((double)result.value)/result.count;
+    }
+
+    @Override
+    public Double aggregateStream(Stream<Long> stream) {
+        final OptionalDouble averageOpt = stream.mapToLong(Long::longValue).average();
+        return averageOpt.isPresent() ? averageOpt.getAsDouble() : null;
+    }
+    
+    /**
+     * @since 2.4
+     */
+    @Override
+    public AverageAccumulator<Long> clone(AverageAccumulator<Long> original) {
+        return new AverageAccumulator<Long>(original.value, original.count);
+    }
+    
+}
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