Update the Combinations generator based on Mark Wilson's array-subset…

…s repository.

src/Generators/Combinations.php

@@ -0,0 +1,76 @@
+<?php
+
+namespace drupol\phpermutations\Generators;
+
+use drupol\phpermutations\Combinatorics;
+
+/**
+ * Class Combinations.
+ *
+ * @package drupol\phpermutations\Generators
+ *
+ * @author  Mark Wilson <[email protected]>
+ */
+class Combinations extends Combinatorics {
+
+  /**
+   * Alias of the get() method.
+   *
+   * @return \Generator
+   *   The prime generator.
+   */
+  public function generator() {
+    return $this->get($this->getDataset(), $this->getLength());
+  }
+
+  /**
+   * The generator.
+   *
+   * @param array $dataset
+   *   The dataset.
+   *
+   * @codingStandardsIgnoreStart
+   * @return \Generator
+   * @codingStandardsIgnoreEnd
+   */
+  protected function get(array $dataset, $length) {
+    $originalLength  = count($dataset);
+    $remainingLength = $originalLength - $length + 1;
+    for ($i = 0; $i < $remainingLength; $i++) {
+      $current = $dataset[$i];
+      if ($length === 1) {
+        yield [$current];
+      } else {
+        $remaining = array_slice($dataset, $i + 1);
+        foreach ($this->get($remaining, $length - 1) as $permutation) {
+          array_unshift($permutation, $current);
+          yield $permutation;
+        }
+      }
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function count() {
+    return $this->fact(count($this->getDataset())) / ($this->fact($this->getLength()) * $this->fact(count($this->getDataset()) - $this->getLength()));
+  }
+
+  /**
+   * Convert the iterator into an array.
+   *
+   * @return array
+   *   The elements.
+   */
+  public function toArray() {
+    $data = array();
+
+    foreach ($this->generator() as $value) {
+      $data[] = $value;
+    }
+
+    return $data;
+  }
+
+}

tests/src/Generators/CombinationsTest.php

@@ -0,0 +1,74 @@
+<?php
+
+namespace drupol\phpermutations\Tests\Generators;
+
+use drupol\phpermutations\Generators\Combinations;
+use drupol\phpermutations\Permutations;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Class PermutationsTest.
+ *
+ * @package drupol\phpermutations\Tests
+ */
+class CombinationsTest extends TestCase {
+
+  /**
+   * The tests.
+   *
+   * @dataProvider simpleValueProvider
+   */
+  public function testCombinationsClass($input, $expected) {
+    $combinations = new Combinations($input['dataset'], $input['length']);
+
+    $this->assertEquals($input['dataset'], $combinations->getDataset());
+    $this->assertEquals($input['length'], $combinations->getLength());
+    $this->assertEquals($expected['dataset'], $combinations->toArray(), "\$canonicalize = true", $delta = 0.0, $maxDepth = 10, $canonicalize = TRUE);
+    $this->assertEquals($expected['count'], $combinations->count());
+  }
+
+  /**
+   * The data provider.
+   *
+   * @return array
+   *   The test input values and their expected output.
+   */
+  public function simpleValueProvider() {
+    return [
+      [
+        'input' => [
+          'dataset' => [1, 2, 3, 4, 5],
+          'length' => 5,
+        ],
+        'output' => [
+          'dataset' => [
+            [1, 2, 3, 4, 5],
+          ],
+          'count' => 1,
+        ],
+      ],
+      [
+        'input' => [
+          'dataset' => [1, 2, 3, 4, 5],
+          'length' => 3,
+        ],
+        'output' => [
+          'dataset' => [
+            [1, 2, 3],
+            [1, 2, 4],
+            [1, 2, 5],
+            [1, 3, 4],
+            [1, 3, 5],
+            [1, 4, 5],
+            [2, 3, 4],
+            [2, 3, 5],
+            [2, 4, 5],
+            [3, 4, 5],
+          ],
+          'count' => 10,
+        ],
+      ],
+    ];
+  }
+
+}