Implementation of the CHITEST() statistical function (#1960)

* Implementation of the CHITEST() statistical function

* A couple of additional edge case tests (rows = 1, columns = 1)

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 
 ### Added
 
+- Implemented the CHITEST() Statistical function.
 - Support for ActiveSheet and SelectedCells in the ODS Reader and Writer. [PR #1908](https://github.com/PHPOffice/PhpSpreadsheet/pull/1908)
 
 ### Changed

src/PhpSpreadsheet/Calculation/Calculation.php

@@ -518,12 +518,12 @@ class Calculation
         ],
         'CHITEST' => [
             'category' => Category::CATEGORY_STATISTICAL,
-            'functionCall' => [Functions::class, 'DUMMY'],
+            'functionCall' => [Statistical\Distributions\ChiSquared::class, 'test'],
             'argumentCount' => '2',
         ],
         'CHISQ.TEST' => [
             'category' => Category::CATEGORY_STATISTICAL,
-            'functionCall' => [Functions::class, 'DUMMY'],
+            'functionCall' => [Statistical\Distributions\ChiSquared::class, 'test'],
             'argumentCount' => '2',
         ],
         'CHOOSE' => [

src/PhpSpreadsheet/Calculation/Statistical/Distributions/ChiSquared.php

@@ -82,4 +82,45 @@ class ChiSquared
 
         return $newtonRaphson->execute($probability);
     }
+
+    public static function test($actual, $expected)
+    {
+        $rows = count($actual);
+        $actual = Functions::flattenArray($actual);
+        $expected = Functions::flattenArray($expected);
+        $columns = count($actual) / $rows;
+
+        $countActuals = count($actual);
+        $countExpected = count($expected);
+        if ($countActuals !== $countExpected || $countActuals === 1) {
+            return Functions::NAN();
+        }
+
+        $result = 0.0;
+        for ($i = 0; $i < $countActuals; ++$i) {
+            if ($expected[$i] == 0.0) {
+                return Functions::DIV0();
+            } elseif ($expected[$i] < 0.0) {
+                return Functions::NAN();
+            }
+            $result += (($actual[$i] - $expected[$i]) ** 2) / $expected[$i];
+        }
+
+        $degrees = self::degrees($rows, $columns);
+
+        $result = self::distribution($result, $degrees);
+
+        return $result;
+    }
+
+    protected static function degrees(int $rows, int $columns): int
+    {
+        if ($rows === 1) {
+            return $columns - 1;
+        } elseif ($columns === 1) {
+            return $rows - 1;
+        }
+
+        return ($columns - 1) * ($rows - 1);
+    }
 }

tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiTestTest.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
+
+use PhpOffice\PhpSpreadsheet\Calculation\Statistical;
+use PHPUnit\Framework\TestCase;
+
+class ChiTestTest extends TestCase
+{
+    /**
+     * @dataProvider providerCHITEST
+     *
+     * @param mixed $expectedResult
+     * @param mixed $actual
+     * @param mixed $expected
+     */
+    public function testCHITEST($expectedResult, $actual, $expected): void
+    {
+        $result = Statistical\Distributions\ChiSquared::test($actual, $expected);
+        self::assertEqualsWithDelta($expectedResult, $result, 1E-12);
+    }
+
+    public function providerCHITEST()
+    {
+        return require 'tests/data/Calculation/Statistical/CHITEST.php';
+    }
+}

tests/data/Calculation/Statistical/CHITEST.php

@@ -0,0 +1,39 @@
+<?php
+
+return [
+    [
+        0.0152703571482,
+        [[112, 76], [85, 95]],
+        [[100, 85], [70, 90]],
+    ],
+    [
+        0.000308192027,
+        [[58, 35], [11, 25], [10, 23]],
+        [[45.35, 47.65], [17.56, 18.44], [16.09, 16.91]],
+    ],
+    [
+        0.015888560447,
+        [[58], [11], [10]],
+        [[45.35], [17.56], [16.09]],
+    ],
+    [
+        0.008682970191,
+        [[58, 35]],
+        [[45.35, 47.65]],
+    ],
+    [
+        '#NUM!',
+        [[58, 11], [10, 35], [25]],
+        [[45.35, 17.56], [16.09, 47.65], [18.44, 16.91]],
+    ],
+    [
+        '#DIV/0!',
+        [[112, 76], [85, 95]],
+        [[100, 0], [70, 90]],
+    ],
+    [
+        '#NUM!',
+        [[112, 76], [85, 95]],
+        [[100, 85], [-70, 90]],
+    ],
+];