KOGITO-8447:[Dashbuilder]Support MEDIAN aggregation function (apache#…

…1406)

* KOGITO-8447:[Dashbuilder]Support MEDIAN aggregation function

* Fixing copyright header

packages/dashbuilder/kie-soup-dataset/kie-soup-dataset-api/src/main/java/org/dashbuilder/dataset/group/AggregateFunctionType.java

@@ -29,10 +29,11 @@ public enum AggregateFunctionType {
     AVERAGE,
     SUM,
     MIN,
-    MAX;
+    MAX,
+    MEDIAN;
 
     private static AggregateFunctionType[] _typeArray = values();
-    private static List<AggregateFunctionType> _numericOnly = Arrays.asList(AVERAGE, SUM, MAX, MIN);
+    private static List<AggregateFunctionType> _numericOnly = Arrays.asList(AVERAGE, MEDIAN, SUM, MAX, MIN);
 
     public int getIndex() {
         for (int i = 0; i < _typeArray.length; i++) {

packages/dashbuilder/kie-soup-dataset/kie-soup-dataset-shared/src/main/java/org/dashbuilder/dataset/engine/function/AggregateFunctionManagerImpl.java

@@ -36,6 +36,7 @@ public AggregateFunctionManagerImpl() {
         registerFunction(new DistinctFunction());
         registerFunction(new SumFunction());
         registerFunction(new AverageFunction());
+        registerFunction(new MedianFunction());
         registerFunction(new MaxFunction());
         registerFunction(new MinFunction());
     }

packages/dashbuilder/kie-soup-dataset/kie-soup-dataset-shared/src/main/java/org/dashbuilder/dataset/engine/function/MedianFunction.java

@@ -0,0 +1,75 @@
+/*
+ * Copyright 2023 Red Hat, Inc. and/or its affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.dashbuilder.dataset.engine.function;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+import org.dashbuilder.dataset.group.AggregateFunctionType;
+
+/**
+ * It calculates the average value of a set of numbers.
+ */
+public class MedianFunction extends AbstractFunction {
+
+    public MedianFunction() {
+        super();
+    }
+
+    public AggregateFunctionType getType() {
+        return AggregateFunctionType.MEDIAN;
+    }
+
+    public Object aggregate(List values) {
+        if (values == null || values.isEmpty()) {
+            return 0d;
+        }
+
+        var n = values.size();
+
+        if (n == 1) {
+            return ((Number) values.get(0)).doubleValue();
+        }
+
+        var sortedValues = values.stream().mapToDouble(v -> ((Number) v).doubleValue()).sorted().toArray();
+
+        if (n % 2 == 1) {
+            return sortedValues[n / 2];
+        }
+        var middle = n / 2;
+        var ii = n == 2 ? 0 : middle - 1;
+        var is = n == 2 ? 1 : middle + 1;
+        var v = (sortedValues[ii] + sortedValues[is]) / 2d;
+        return round(v, precission);
+    }
+
+    public Object aggregate(List values, List<Integer> rows) {
+        if (rows == null) {
+            return aggregate(values);
+        }
+        if (rows.isEmpty()) {
+            return 0d;
+        }
+        if (values == null || values.isEmpty()) {
+            return 0d;
+        }
+        var _values = rows.stream()
+                .map(values::get)
+                .collect(Collectors.toList());
+        return this.aggregate(_values);
+    }
+
+}

packages/dashbuilder/kie-soup-dataset/kie-soup-dataset-shared/src/test/java/org/dashbuilder/dataset/engine/function/AggregateFunctionsTest.java

@@ -336,4 +336,20 @@ public void testAvgFunctionEmpty() {
         Object result = function.aggregate(EMPTY_LIST);
         assertEquals(result, 0d);
     }
+
+    @Test
+    public void testMedianFunction() {
+        var function = new MedianFunction();
+        var values = List.of(1, 2, 3);
+        var result = function.aggregate(values);
+        assertEquals(result, 2d);
+
+        values = List.of(1, 4);
+        result = function.aggregate(values);
+        assertEquals(result, 2.5d);
+
+        values = List.of(1);
+        result = function.aggregate(values);
+        assertEquals(result, 1.0d);
+    }
 }