add FORECAST and FORECAST.LINEAR functions

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1901689 13f79535-47bb-0310-9956-ffa450edef68

8 files changed, 169 insertions, 7 deletions

diff --git a/poi/src/main/java/org/apache/poi/ss/formula/atp/AnalysisToolPak.java b/poi/src/main/java/org/apache/poi/ss/formula/atp/AnalysisToolPak.java
index af7c4c0aa1..dd165383ee 100644
--- a/poi/src/main/java/org/apache/poi/ss/formula/atp/AnalysisToolPak.java
+++ b/poi/src/main/java/org/apache/poi/ss/formula/atp/AnalysisToolPak.java
@@ -118,6 +118,7 @@ public final class AnalysisToolPak implements UDFFinder {
         r(m, "FACTDOUBLE", FactDouble.instance);
         r(m, "FLOOR.MATH", FloorMath.instance);
         r(m, "FLOOR.PRECISE", FloorPrecise.instance);
+        r(m, "FORECAST.LINEAR", Forecast.instance);
         r(m, "FVSCHEDULE", null);
         r(m, "GCD", Gcd.instance);
         r(m, "GESTEP", null);
diff --git a/poi/src/main/java/org/apache/poi/ss/formula/eval/FunctionEval.java b/poi/src/main/java/org/apache/poi/ss/formula/eval/FunctionEval.java
index c544d4680a..6693cc5459 100644
--- a/poi/src/main/java/org/apache/poi/ss/formula/eval/FunctionEval.java
+++ b/poi/src/main/java/org/apache/poi/ss/formula/eval/FunctionEval.java
@@ -289,7 +289,7 @@ public final class FunctionEval {
         // 306: CHITEST
         retval[307] = Correl.instance;
         retval[308] = Covar.instanceP;
-        // 309: FORECAST
+        retval[309] = Forecast.instance;
         // 310: FTEST
         retval[311] = new Intercept();
         retval[312] = Correl.instance;
diff --git a/poi/src/main/java/org/apache/poi/ss/formula/functions/TwoArrayFunction.java b/poi/src/main/java/org/apache/poi/ss/formula/functions/ArrayFunctionUtils.java
index c4cce8449a..3dbedd2ae6 100644
--- a/poi/src/main/java/org/apache/poi/ss/formula/functions/TwoArrayFunction.java
+++ b/poi/src/main/java/org/apache/poi/ss/formula/functions/ArrayFunctionUtils.java
@@ -30,9 +30,9 @@ import org.apache.poi.ss.formula.eval.ValueEval;
 import java.util.Arrays;
 import java.util.List;
 
-abstract class TwoArrayFunction extends Fixed2ArgFunction {
+final class ArrayFunctionUtils {
 
-    protected List<DoubleList> getNumberArrays(ValueEval operand0, ValueEval operand1) throws EvaluationException {
+    static List<DoubleList> getNumberArrays(ValueEval operand0, ValueEval operand1) throws EvaluationException {
         double[] retval0 = collectValuesWithBlanks(operand0).toArray();
         double[] retval1 = collectValuesWithBlanks(operand1).toArray();
         if (retval0.length != retval1.length) {
@@ -52,7 +52,7 @@ abstract class TwoArrayFunction extends Fixed2ArgFunction {
         return Arrays.asList(filtered0, filtered1);
     }
 
-    private DoubleList collectValuesWithBlanks(ValueEval operand) throws EvaluationException {
+    private static DoubleList collectValuesWithBlanks(ValueEval operand) throws EvaluationException {
         DoubleList doubleList = new DoubleList();
         if (operand instanceof ThreeDEval) {
             ThreeDEval ae = (ThreeDEval) operand;
@@ -111,7 +111,7 @@ abstract class TwoArrayFunction extends Fixed2ArgFunction {
         return doubleList;
     }
 
-    private Double collectValue(ValueEval ve) throws EvaluationException {
+    private static Double collectValue(ValueEval ve) throws EvaluationException {
         if (ve == null) {
             throw new IllegalArgumentException("ve must not be null");
         }
diff --git a/poi/src/main/java/org/apache/poi/ss/formula/functions/Correl.java b/poi/src/main/java/org/apache/poi/ss/formula/functions/Correl.java
index 0228873549..0aef78249a 100644
--- a/poi/src/main/java/org/apache/poi/ss/formula/functions/Correl.java
+++ b/poi/src/main/java/org/apache/poi/ss/formula/functions/Correl.java
@@ -24,6 +24,8 @@ import org.apache.poi.ss.formula.eval.ValueEval;
 
 import java.util.List;
 
+import static org.apache.poi.ss.formula.functions.ArrayFunctionUtils.getNumberArrays;
+
 /**
  * Implementation for Excel CORREL() function.
  * <p>
@@ -38,7 +40,7 @@ import java.util.List;
  *   See https://support.microsoft.com/en-us/office/correl-function-995dcef7-0c0a-4bed-a3fb-239d7b68ca92
  * </p>
  */
-public class Correl extends TwoArrayFunction {
+public class Correl extends Fixed2ArgFunction {
 
     public static final Correl instance = new Correl();
 
diff --git a/poi/src/main/java/org/apache/poi/ss/formula/functions/Covar.java b/poi/src/main/java/org/apache/poi/ss/formula/functions/Covar.java
index ac838837e4..249233e243 100644
--- a/poi/src/main/java/org/apache/poi/ss/formula/functions/Covar.java
+++ b/poi/src/main/java/org/apache/poi/ss/formula/functions/Covar.java
@@ -26,6 +26,8 @@ import org.apache.poi.ss.formula.eval.ValueEval;
 
 import java.util.List;
 
+import static org.apache.poi.ss.formula.functions.ArrayFunctionUtils.getNumberArrays;
+
 /**
  * Implementation for Excel COVAR() and COVARIANCE.P() functions.
  * <p>
@@ -35,7 +37,7 @@ import java.util.List;
  * @see <a href="https://support.microsoft.com/en-us/office/covariance-p-function-6f0e1e6d-956d-4e4b-9943-cfef0bf9edfc">COVARIANCE.P</a>
  * </p>
  */
-public class Covar extends TwoArrayFunction implements FreeRefFunction {
+public class Covar extends Fixed2ArgFunction implements FreeRefFunction {
 
     public static final Covar instanceP = new Covar(false);
     public static final Covar instanceS = new Covar(true);
diff --git a/poi/src/main/java/org/apache/poi/ss/formula/functions/Forecast.java b/poi/src/main/java/org/apache/poi/ss/formula/functions/Forecast.java
new file mode 100644
index 0000000000..b6b3f1c5f5
--- /dev/null
+++ b/poi/src/main/java/org/apache/poi/ss/formula/functions/Forecast.java
@@ -0,0 +1,93 @@
+/* ====================================================================
+   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.OperationEvaluationContext;
+import org.apache.poi.ss.formula.eval.ErrorEval;
+import org.apache.poi.ss.formula.eval.EvaluationException;
+import org.apache.poi.ss.formula.eval.NumberEval;
+import org.apache.poi.ss.formula.eval.OperandResolver;
+import org.apache.poi.ss.formula.eval.ValueEval;
+
+import java.util.List;
+
+import static org.apache.poi.ss.formula.functions.ArrayFunctionUtils.getNumberArrays;
+
+/**
+ * Implementation for Excel FORECAST() and FORECAST.LINEAR() functions.
+ * <p>
+ *   <b>Syntax</b>:<br> <b>FORECAST </b>(<b>number</b>, <b>array1</b>, <b>array2</b>)<br>
+ * </p>
+ * <p>
+ *   See https://support.microsoft.com/en-us/office/forecast-and-forecast-linear-functions-50ca49c9-7b40-4892-94e4-7ad38bbeda99
+ * </p>
+ */
+public class Forecast extends Fixed3ArgFunction implements FreeRefFunction {
+
+    public static final Forecast instance = new Forecast();
+
+    private Forecast() {}
+
+    @Override
+    public ValueEval evaluate(int srcRowIndex, int srcColumnIndex, ValueEval arg0, ValueEval arg1, ValueEval arg2) {
+        try {
+            final Double x = evaluateValue(arg0, srcRowIndex, srcColumnIndex);
+            if (x == null || x.isNaN() || x.isInfinite()) {
+                return ErrorEval.VALUE_INVALID;
+            }
+            final List<DoubleList> arrays = getNumberArrays(arg1, arg2);
+            final double[] arrY = arrays.get(0).toArray();
+            final double[] arrX = arrays.get(1).toArray();
+            final double averageY = MathX.average(arrY);
+            final double averageX = MathX.average(arrX);
+            double bnum = 0;
+            double bdem = 0;
+            final int len = arrY.length;
+            for (int i = 0; i < len; i++) {
+                double diff0 = arrX[i] - averageX;
+                bnum += diff0 * (arrY[i] - averageY);
+                bdem += Math.pow(diff0, 2);
+            }
+            if (bdem == 0) {
+                return ErrorEval.DIV_ZERO;
+            }
+
+            final double b = bnum / bdem;
+            final double a = averageY - (b * averageX);
+            final double res = a + (b * x);
+            return new NumberEval(res);
+        } catch (EvaluationException e) {
+            return e.getErrorEval();
+        } catch (Exception e) {
+            return ErrorEval.NA;
+        }
+    }
+
+    @Override
+    public ValueEval evaluate(ValueEval[] args, OperationEvaluationContext ec) {
+        if (args.length != 3) {
+            return ErrorEval.VALUE_INVALID;
+        }
+        return evaluate(ec.getRowIndex(), ec.getColumnIndex(), args[0], args[1], args[2]);
+    }
+
+    private static Double evaluateValue(ValueEval arg, int srcRowIndex, int srcColumnIndex) throws EvaluationException {
+        ValueEval veText = OperandResolver.getSingleValue(arg, srcRowIndex, srcColumnIndex);
+        String strText1 = OperandResolver.coerceValueToString(veText);
+        return OperandResolver.parseDouble(strText1);
+    }
+}
diff --git a/poi/src/test/java/org/apache/poi/ss/formula/functions/TestCorrel.java b/poi/src/test/java/org/apache/poi/ss/formula/functions/TestCorrel.java
index 3be25d2c23..58091ac21c 100644
--- a/poi/src/test/java/org/apache/poi/ss/formula/functions/TestCorrel.java
+++ b/poi/src/test/java/org/apache/poi/ss/formula/functions/TestCorrel.java
@@ -60,6 +60,7 @@ final class TestCorrel {
             assertDouble(fe, cell, "PEARSON(A2:A6,B2:B6)", 0.699379, 0.0000005);
         }
     }
+
     @Test
     void testBlankValue() throws IOException {
         try (HSSFWorkbook wb = initWorkbook1(null)) {
diff --git a/poi/src/test/java/org/apache/poi/ss/formula/functions/TestForecast.java b/poi/src/test/java/org/apache/poi/ss/formula/functions/TestForecast.java
new file mode 100644
index 0000000000..e2e42e110d
--- /dev/null
+++ b/poi/src/test/java/org/apache/poi/ss/formula/functions/TestForecast.java
@@ -0,0 +1,63 @@
+/* ====================================================================
+   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.HSSFRow;
+import org.apache.poi.hssf.usermodel.HSSFSheet;
+import org.apache.poi.hssf.usermodel.HSSFWorkbook;
+import org.apache.poi.ss.usermodel.FormulaError;
+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;
+import static org.apache.poi.ss.util.Utils.assertError;
+
+/**
+ * Tests for {@link Forecast}
+ */
+final class TestForecast {
+
+    //https://support.microsoft.com/en-us/office/forecast-and-forecast-linear-functions-50ca49c9-7b40-4892-94e4-7ad38bbeda99
+    @Test
+    void testMicrosoftExample1() throws IOException {
+        try (HSSFWorkbook wb = initWorkbook1()) {
+            HSSFSheet sheet = wb.getSheetAt(0);
+            HSSFRow row = sheet.getRow(0);
+            HSSFCell cell = row.createCell(100);
+            HSSFFormulaEvaluator fe = new HSSFFormulaEvaluator(wb);
+            assertDouble(fe, cell, "FORECAST(30,A2:A6,B2:B6)", 10.607253, 0.0000001);
+            assertDouble(fe, cell, "FORECAST.LINEAR(30,A2:A6,B2:B6)", 10.607253, 0.0000001);
+        }
+    }
+
+    private HSSFWorkbook initWorkbook1() {
+        HSSFWorkbook wb = new HSSFWorkbook();
+        HSSFSheet sheet = wb.createSheet();
+        addRow(sheet, 0, "Known X", "Known Y");
+        addRow(sheet, 1, 6, 20);
+        addRow(sheet, 2, 7, 28);
+        addRow(sheet, 3, 9, 31);
+        addRow(sheet, 4, 15, 38);
+        addRow(sheet, 5, 21, 40);
+        return wb;
+    }
+}