From ad2634e32ac80e32d69b5fc0451363cd384215a0 Mon Sep 17 00:00:00 2001
From: Dennis Eichhorn <spl1nes.com@googlemail.com>
Date: Sun, 14 Jun 2020 00:08:16 +0200
Subject: [PATCH] implemented pagerank algorithm

---
 Business/Marketing/PageRank.php           | 133 ++++++++++++++++++++++
 tests/Business/Marketing/PageRankTest.php |  77 +++++++++++++
 2 files changed, 210 insertions(+)
 create mode 100644 Business/Marketing/PageRank.php
 create mode 100644 tests/Business/Marketing/PageRankTest.php

diff --git a/Business/Marketing/PageRank.php b/Business/Marketing/PageRank.php
new file mode 100644
index 000000000..cf629918b
--- /dev/null
+++ b/Business/Marketing/PageRank.php
@@ -0,0 +1,133 @@
+<?php
+/**
+ * Orange Management
+ *
+ * PHP Version 7.4
+ *
+ * @package   phpOMS\Business\Marketing
+ * @copyright Dennis Eichhorn
+ * @license   OMS License 1.0
+ * @version   1.0.0
+ * @link      https://orange-management.org
+ */
+declare(strict_types=1);
+
+namespace phpOMS\Business\Marketing;
+
+/**
+ * PageRank algorithm
+ *
+ * @package phpOMS\Business\Marketing
+ * @license OMS License 1.0
+ * @link    https://orange-management.org
+ * @since   1.0.0
+ */
+final class PageRank
+{
+    /**
+     * Damping value
+     *
+     * @var float
+     * @since 1.0.0
+     */
+    private float $damping = 0.85;
+
+    /**
+     * Page rank
+     *
+     * @var array<mixed, float>
+     * @since 1.0.0
+     */
+    private array $pageRanks = [];
+
+    /**
+     * Relation array
+     *
+     * Array of elements where every element has an array of incoming links/relations
+     *
+     * @var array[]
+     * @since 1.0.0
+     */
+    private array $relations = [];
+
+    /**
+     * Amount of outgoing links from an element
+     *
+     * @var int[]
+     * @since 1.0.0
+     */
+    private array $outgoing = [];
+
+    /**
+     * Constructor.
+     *
+     * @param array[] $relations Relations between elements (keys => link from, array => link to)
+     * @param bool    $isUnique  Only consider unique relations
+     * @param float   $damping   Damping value
+     *
+     * @since 1.0.0
+     */
+    public function __construct(array $relations, bool $isUnique = true, float $damping = 0.85)
+    {
+        $this->damping = $damping;
+
+        foreach ($relations as $key => $relation) {
+            $this->outgoing[$key] = \count($relation);
+
+            if (!isset($this->relations[$key])) {
+                $this->relations[$key] = [];
+            }
+
+            foreach ($relation as $linkTo) {
+                if (!isset($this->relations[$linkTo])) {
+                    $this->relations[$linkTo] = [];
+                }
+
+                if (!isset($this->outgoing[$linkTo])) {
+                    $this->outgoing[$linkTo] = 0;
+                }
+
+                if (!$isUnique || !\in_array($key, $this->relations[$linkTo])) {
+                    $this->relations[$linkTo][] = $key;
+                }
+            }
+        }
+    }
+
+    /**
+     * Calcualte the rank based on a start rank for the different elements
+     *
+     * A different start rank for different elements might make sense if the elements are not uniform from the very beginning
+     *
+     * @param int                      $iterations Algorithm iterations
+     * @param null|array<mixed, float> $startRank  Start rank for an element
+     *
+     * @return array
+     *
+     * @since 1.0.0
+     */
+    public function calculateRanks(int $iterations = 20, array $startRank = null) : array
+    {
+        if ($startRank !== null) {
+            $this->pageRanks = $startRank;
+        } else {
+            foreach ($this->relations as $key => $relation) {
+                $this->pageRanks[$key] = 0.0;
+            }
+        }
+
+        for ($i = 0; $i < $iterations; ++$i) {
+            foreach ($this->relations as $key => $relation) {
+                $PR  = 0.0;
+
+                foreach ($relation as $linkFrom) {
+                    $PR += $this->pageRanks[$linkFrom] / $this->outgoing[$linkFrom];
+                }
+
+                $this->pageRanks[$key] = 1 - $this->damping + $this->damping * $PR;
+            }
+        }
+
+        return $this->pageRanks;
+    }
+}
diff --git a/tests/Business/Marketing/PageRankTest.php b/tests/Business/Marketing/PageRankTest.php
new file mode 100644
index 000000000..36da563d3
--- /dev/null
+++ b/tests/Business/Marketing/PageRankTest.php
@@ -0,0 +1,77 @@
+<?php
+/**
+ * Orange Management
+ *
+ * PHP Version 7.4
+ *
+ * @package   tests
+ * @copyright Dennis Eichhorn
+ * @license   OMS License 1.0
+ * @version   1.0.0
+ * @link      https://orange-management.org
+ */
+declare(strict_types=1);
+
+namespace phpOMS\tests\Business\Marketing;
+
+use phpOMS\Business\Marketing\PageRank;
+
+/**
+ * @testdox phpOMS\tests\Business\Marketing\PageRankTest: Page rank algorithm
+ *
+ * @internal
+ */
+class PageRankTest extends \PHPUnit\Framework\TestCase
+{
+    /**
+     * @testdox Test the correctness of the page rank algorithm
+     * @group framework
+     */
+    public function testPageRank() : void
+    {
+        $relations = [
+            'A' => ['B', 'C'],
+            'B' => ['C'],
+            'C' => ['A'],
+            'D' => ['C'],
+        ];
+
+        $ranking = new PageRank($relations, true);
+
+        self::assertEqualsWithDelta(
+            [
+                'A' => 1.49,
+                'B' => 0.78,
+                'C' => 1.58,
+                'D' => 0.15,
+            ],
+            $ranking->calculateRanks(20, null),
+            0.01
+        );
+    }
+
+    /**
+     * @testdox Test the correctness of the page rank algorithm with custom damping and starting values
+     * @group framework
+     */
+    public function testPageRankCustomDampingAndStart() : void
+    {
+        $relations = [
+            'A' => ['B', 'C'],
+            'B' => ['C'],
+            'C' => ['A'],
+        ];
+
+        $ranking = new PageRank($relations, true, 0.5);
+
+        self::assertEqualsWithDelta(
+            [
+                'A' => 1.0769,
+                'B' => 0.769,
+                'C' => 1.1538,
+            ],
+            $ranking->calculateRanks(20, ['A' => 1.0, 'B' => 1.0, 'C' => 1.0]),
+            0.01
+        );
+    }
+}