add DVAR function support

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1901274 13f79535-47bb-0310-9956-ffa450edef68

poi/src/main/java/org/apache/poi/ss/formula/eval/FunctionEval.java

@@ -112,7 +112,7 @@ public final class FunctionEval {
         retval[44] = new DStarRunner(DStarRunner.DStarAlgorithmEnum.DMAX);
         retval[45] = new DStarRunner(DStarRunner.DStarAlgorithmEnum.DSTDEV);
         retval[46] = AggregateFunction.VAR;
-        // 47: DVAR
+        retval[47] = new DStarRunner(DStarRunner.DStarAlgorithmEnum.DVAR);
         retval[48] = TextFunction.TEXT;
         // 49: LINEST
         retval[50] = new Trend();

poi/src/main/java/org/apache/poi/ss/formula/functions/DStarRunner.java

@@ -23,7 +23,6 @@ import org.apache.poi.ss.formula.eval.AreaEval;
 import org.apache.poi.ss.formula.eval.BlankEval;
 import org.apache.poi.ss.formula.eval.ErrorEval;
 import org.apache.poi.ss.formula.eval.EvaluationException;
-import org.apache.poi.ss.formula.eval.MissingArgEval;
 import org.apache.poi.ss.formula.eval.NotImplementedException;
 import org.apache.poi.ss.formula.eval.NumberEval;
 import org.apache.poi.ss.formula.eval.NumericValueEval;
@@ -64,6 +63,8 @@ public final class DStarRunner implements Function3Arg {
         DAVERAGE(DAverage::new),
         /** @see DStdev */
         DSTDEV(DStdev::new),
+        /** @see DVar */
+        DVAR(DVar::new),
         ;
 
         private final Supplier<IDStarAlgorithm> implSupplier;

poi/src/main/java/org/apache/poi/ss/formula/functions/DVar.java

@@ -0,0 +1,54 @@
+/* ====================================================================
+   Licensed to the Apache Software Foundation (ASF) under one or more
+   contributor license agreements.  See the NOTICE file distributed with
+   this work for additional information regarding copyright ownership.
+   The ASF licenses this file to You 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.apache.poi.ss.formula.functions;
+
+import org.apache.poi.ss.formula.eval.NumberEval;
+import org.apache.poi.ss.formula.eval.NumericValueEval;
+import org.apache.poi.ss.formula.eval.ValueEval;
+import org.apache.poi.ss.util.NumberToTextConverter;
+
+import java.math.BigDecimal;
+import java.util.ArrayList;
+
+/**
+ * Implementation of the DVar function:
+ * Gets the variance value of a column in an area with given conditions.
+ */
+public final class DVar implements IDStarAlgorithm {
+    private final ArrayList<Double> values = new ArrayList<>();
+
+    @Override
+    public boolean processMatch(ValueEval eval) {
+        if (eval instanceof NumericValueEval) {
+            final double val = ((NumericValueEval)eval).getNumberValue();
+            values.add(val);
+        }
+        return true;
+    }
+
+    @Override
+    public ValueEval getResult() {
+        final double[] array = new double[values.size()];
+        int pos = 0;
+        for (Double d : values) {
+            array[pos++] = d;
+        }
+        final double var = StatsLib.var(array);
+        return new NumberEval(new BigDecimal(NumberToTextConverter.toText(var)).doubleValue());
+    }
+}

poi/src/test/java/org/apache/poi/ss/formula/functions/TestDVar.java

@@ -0,0 +1,61 @@
+
+/* ====================================================================
+   Licensed to the Apache Software Foundation (ASF) under one or more
+   contributor license agreements.  See the NOTICE file distributed with
+   this work for additional information regarding copyright ownership.
+   The ASF licenses this file to You 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.apache.poi.ss.formula.functions;
+
+import org.apache.poi.hssf.usermodel.HSSFCell;
+import org.apache.poi.hssf.usermodel.HSSFFormulaEvaluator;
+import org.apache.poi.hssf.usermodel.HSSFSheet;
+import org.apache.poi.hssf.usermodel.HSSFWorkbook;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+
+import static org.apache.poi.ss.util.Utils.addRow;
+import static org.apache.poi.ss.util.Utils.assertDouble;
+
+/**
+ * Testcase for function DVAR()
+ */
+public class TestDVar {
+
+    //https://support.microsoft.com/en-us/office/dvar-function-d6747ca9-99c7-48bb-996e-9d7af00f3ed1
+    @Test
+    void testMicrosoftExample1() throws IOException {
+        try (HSSFWorkbook wb = initWorkbook1()) {
+            HSSFFormulaEvaluator fe = new HSSFFormulaEvaluator(wb);
+            HSSFCell cell = wb.getSheetAt(0).getRow(0).createCell(12);
+            assertDouble(fe, cell, "DVAR(A4:E10, \"Yield\", A1:A3)", 8.8, 0.0000000001);
+        }
+    }
+
+    private HSSFWorkbook initWorkbook1() {
+        HSSFWorkbook wb = new HSSFWorkbook();
+        HSSFSheet sheet = wb.createSheet();
+        addRow(sheet, 0, "Tree", "Height", "Age", "Yield", "Profit", "Height");
+        addRow(sheet, 1, "=Apple", ">10", null, null, null, "<16");
+        addRow(sheet, 2, "=Pear");
+        addRow(sheet, 3, "Tree", "Height", "Age", "Yield", "Profit");
+        addRow(sheet, 4, "Apple", 18, 20, 14, 105);
+        addRow(sheet, 5, "Pear", 12, 12, 10, 96);
+        addRow(sheet, 6, "Cherry", 13, 14, 9, 105);
+        addRow(sheet, 7, "Apple", 14, 15, 10, 75);
+        addRow(sheet, 8, "Pear", 9, 8, 8, 77);
+        addRow(sheet, 9, "Apple", 8, 9, 6, 45);
+        return wb;
+    }
+}