Grouping Associative Arrays by a Common Key in PHP

<?php

/**
 * Groups an array of associative arrays by a specified key.
 *
 * @param array $data The array of associative arrays to group.
 * @param string $key The key by which to group the arrays.
 * @return array The grouped array.
 */
function groupArrayByKey(array $data, string $key): array
{
    $grouped = [];
    foreach ($data as $item) {
        if (isset($item[$key])) {
            $grouped[$item[$key]][] = $item;
        } else {
            // Handle items without the specified key, e.g., place in a 'null' group
            $grouped['[ungrouped]'][] = $item; 
        }
    }
    return $grouped;
}

// Example Usage:
$products = [
    ['id' => 1, 'name' => 'Laptop', 'category' => 'Electronics', 'price' => 1200],
    ['id' => 2, 'name' => 'Mouse', 'category' => 'Electronics', 'price' => 25],
    ['id' => 3, 'name' => 'Book', 'category' => 'Books', 'price' => 15],
    ['id' => 4, 'name' => 'Keyboard', 'category' => 'Electronics', 'price' => 75],
    ['id' => 5, 'name' => 'Magazine', 'category' => 'Books', 'price' => 10],
    ['id' => 6, 'name' => 'Headphones', 'category' => 'Audio', 'price' => 150],
    ['id' => 7, 'name' => 'Tablet', 'category' => 'Electronics', 'price' => 500],
];

echo "Original Products:
";
foreach ($products as $product) {
    echo json_encode($product) . "
";
}

$groupedByCategory = groupArrayByKey($products, 'category');

echo "
Grouped by Category:
";
foreach ($groupedByCategory as $category => $items) {
    echo "--- " . $category . " ---
";
    foreach ($items as $item) {
        echo "- " . $item['name'] . "
";
    }
}
?>