<code lang="php">
$arr = array(
  2021 => array(
    1 => "1",
    2 => "1"
  ),
  2022 => array (
    4 => "1",
    5 => "1",
    6 => "1",
    7 => "1"
  )
);
asort($arr);
foreach ($arr as $key => $val) {
    foreach ($arr[$key] as $key_2 => $val_2) {
        echo $key ."-".$key_2."<br>";
    }
}
</code>