add STDEVP function support

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1901279 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -204,6 +204,7 @@ public final class FunctionEval {
         retval[189] = new DStarRunner(DStarRunner.DStarAlgorithmEnum.DPRODUCT);
         retval[190] = LogicalFunction.ISNONTEXT;
 
+        retval[193] = AggregateFunction.STDEVP;
         retval[194] = AggregateFunction.VARP;
         // 195: DSTDEVP
         // 196: DVARP

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

@@ -228,6 +228,14 @@ public abstract class AggregateFunction extends MultiOperandNumericFunction {
             return StatsLib.stdev(values);
         }
     };
+    public static final Function STDEVP = new AggregateFunction() {
+        protected double evaluate(double[] values) throws EvaluationException {
+            if (values.length < 1) {
+                throw new EvaluationException(ErrorEval.DIV_ZERO);
+            }
+            return StatsLib.stdevp(values);
+        }
+    };
     public static final Function SUM = new AggregateFunction() {
         protected double evaluate(double[] values) {
             return MathX.sum(values);

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

@@ -57,6 +57,14 @@ final class StatsLib {
         return r;
     }
 
+    public static double stdevp(double[] v) {
+        double r = Double.NaN;
+        if (v!=null && v.length > 1) {
+            r = Math.sqrt( devsq(v) / v.length );
+        }
+        return r;
+    }
+
     public static double var(double[] v) {
         double r = Double.NaN;
         if (v!=null && v.length > 1) {

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

@@ -0,0 +1,64 @@
+
+/* ====================================================================
+   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 STDEVP()
+ */
+public class TestStdevp {
+
+    //https://support.microsoft.com/en-us/office/stdevp-function-1f7c1c88-1bec-4422-8242-e9f7dc8bb195
+    @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, "STDEVP(A3:A12)", 26.0545581424825, 0.00000000001);
+            assertDouble(fe, cell, "STDEV(A3:A12)", 27.4639157198435, 0.00000000001);
+        }
+    }
+
+    private HSSFWorkbook initWorkbook1() {
+        HSSFWorkbook wb = new HSSFWorkbook();
+        HSSFSheet sheet = wb.createSheet();
+        addRow(sheet, 0, "Data");
+        addRow(sheet, 1, "Strength");
+        addRow(sheet, 2, 1345);
+        addRow(sheet, 3, 1301);
+        addRow(sheet, 4, 1368);
+        addRow(sheet, 5, 1322);
+        addRow(sheet, 6, 1310);
+        addRow(sheet, 7, 1370);
+        addRow(sheet, 8, 1318);
+        addRow(sheet, 9, 1350);
+        addRow(sheet, 10, 1303);
+        addRow(sheet, 11, 1299);
+        return wb;
+    }
+}