added filter |group [WIP]

src/Latte/Essential/CoreExtension.php

@@ -135,6 +135,7 @@ public function getFilters(): array
 				? [$this->filters, 'firstUpper']
 				: fn() => throw new RuntimeException('Filter |firstUpper requires mbstring extension.'),
 			'floor' => [$this->filters, 'floor'],
+			'group' => [$this->filters, 'group'],
 			'implode' => [$this->filters, 'implode'],
 			'indent' => [$this->filters, 'indent'],
 			'join' => [$this->filters, 'implode'],

src/Latte/Essential/Filters.php

@@ -483,7 +483,7 @@ public static function sort(
 			$values[] = $value;
 		}
 		$byKey ? uasort($keys, $comparison) : uasort($values, $comparison);
-		
+
 		return $byKey
 			? (static function () use ($keys, $values): \Generator {
 				foreach ($keys as $i => $key) {
@@ -498,6 +498,38 @@ public static function sort(
 	}
 
 
+	/**
+	 * Groups elements by the element indices and preserves the key association and order.
+	 */
+	public static function group(iterable $iterable, string|int|\Closure $by): \Generator
+	{
+		$fn = $by instanceof \Closure ? $by : fn($a) => is_array($a) ? $a[$by] : $a->$by;
+		$keys = $groups = $prevKey = [];
+
+		foreach ($iterable as $k => $v) {
+			$groupKey = $fn($v, $k);
+			if (!$groups || $prevKey !== $groupKey) {
+				$index = array_search($groupKey, $keys, true);
+				if ($index === false) {
+					$index = count($keys);
+					$keys[$index] = $groupKey;
+				}
+				$prevKey = $groupKey;
+			}
+			$groups[$index][0][] = $k;
+			$groups[$index][1][] = $v;
+		}
+
+		foreach ($groups as $index => $pair) {
+			yield $keys[$index] => (static function () use ($pair): \Generator {
+				foreach ($pair[1] as $i => $value) {
+					yield $pair[0][$i] => $value;
+				}
+			})();
+		}
+	}
+
+
 	/**
 	 * Returns value clamped to the inclusive range of min and max.
 	 */

tests/filters/group.phpt

@@ -0,0 +1,88 @@
+<?php
+
+/**
+ * Test: Latte\Essential\Filters::group()
+ */
+
+declare(strict_types=1);
+
+use Latte\Essential\Filters;
+use Tester\Assert;
+
+require __DIR__ . '/../bootstrap.php';
+
+
+function iterator(): Generator
+{
+	yield ['a' => 55] => ['k' => 22, 'k2'];
+	yield ['a' => 66] => (object) ['k' => 22, 'k2'];
+	yield ['a' => 77] => ['k' => 11];
+	yield ['a' => 88] => ['k' => 33];
+}
+
+
+function exportIterator(Traversable $iterator): array
+{
+	$res = [];
+	foreach ($iterator as $key => $value) {
+		$res[] = [$key, $value instanceof Traversable ? exportIterator($value) : $value];
+	}
+	return $res;
+}
+
+
+test('array', function () {
+	Assert::equal(
+		[
+			[22, [
+				[0, ['k' => 22, 'k2']],
+				[1, (object) ['k' => 22, 'k2']],
+			]],
+			[11, [[2, ['k' => 11]]]],
+			[33, [[3, ['k' => 33]]]],
+		],
+		exportIterator(Filters::group(
+			[['k' => 22, 'k2'], (object) ['k' => 22, 'k2'], ['k' => 11], ['k' => 33]],
+			'k',
+		)),
+	);
+	Assert::same([], exportIterator(Filters::group([], 'k')));
+});
+
+
+test('iterator', function () {
+	Assert::equal(
+		[
+			[22, [
+				[['a' => 55], ['k' => 22, 'k2']],
+				[['a' => 66], (object) ['k' => 22, 'k2']],
+			]],
+			[11, [[['a' => 77], ['k' => 11]]]],
+			[33, [[['a' => 88], ['k' => 33]]]],
+		],
+		exportIterator(Filters::group(iterator(), 'k')),
+	);
+});
+
+
+test('callback + array', function () {
+	Assert::same(
+		[[220, [[0, 22]]], [110, [[1, 11]]], [330, [[2, 33]]]],
+		exportIterator(Filters::group([22, 11, 33], fn($a) => $a * 10)),
+	);
+});
+
+
+test('callback + iterator', function () {
+	Assert::equal(
+		[
+			[-22, [
+				[['a' => 55], ['k' => 22, 'k2']],
+				[['a' => 66], (object) ['k' => 22, 'k2']],
+			]],
+			[-11, [[['a' => 77], ['k' => 11]]]],
+			[-33, [[['a' => 88], ['k' => 33]]]],
+		],
+		exportIterator(Filters::group(iterator(), fn($a) => -((array) $a)['k'])),
+	);
+});