サブ配列を 1 つの列でグループ化し、別の列からカンマ区切りの値を生成するにはどうすればよいですか?

$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">$data = []; 
$groups = [];

foreach($data as $item){
    if(!array_key_exists($item[1], $groups)){
        $groups[$item[1]] = [];
    }
    $groups[$item[1]][] = $item[0];
}

$structured = [];
foreach($groups as $group => $values){
    $structured[] = [implode(',', $values), $group];
}</code>