PHP でサブ配列をグループ化し、列ごとに値をフォーマットする方法

$array = [
    ["444", "0081"],
    ["449", "0081"],
    ["451", "0081"],
    ["455", "2100"],
    ["469", "2100"]
];

array (
  0 => 
  array (
    0 => '444,449,451',
    1 => '0081',
  ),
  1 => 
  array (
    0 => '455,469',
    1 => '2100',
  ),
)

<code class="php">// Create an empty array to store the grouped data
$groups = [];

// Loop through the input array
foreach ($array as $item) {
    // If the second column value is not yet a key in $groups, create an empty array for it
    if (!array_key_exists($item[1], $groups)) {
        $groups[$item[1]] = [];
    }
    
    // Add the first column value to the array at the corresponding key
    $groups[$item[1]][] = $item[0];
}

// Initialize the new array with the desired structure
$structured = [];

// Loop through the groups
foreach ($groups as $group => $values) {
    // Join the first column values with commas and add the group key as the second column
    $structured[] = [implode(',', $values), $group];
}</code>