问在PHP中将数组元素移到顶部

EN

$arr = array(
    'a1'=>'1',
    'a2'=>'2'
);

end($arr);

$last_key     = key($arr);
$last_value   = array_pop($arr);
$arr          = array_merge(array($last_key => $last_value), $arr);

/*
    print_r($arr);

    will output (this is tested):
    Array ( [a2] => 2 [a1] => 1 )
*/

function move_to_top(&$array, $key) {
    $temp = array($key => $array[$key]);
    unset($array[$key]);
    $array = $temp + $array;
}

function move_to_bottom(&$array, $key) {
    $value = $array[$key];
    unset($array[$key]);
    $array[$key] = $value;
}

$key = 'a3';
$arr = [
    'a1' => '1',
    'a2' => '2',
    'a3' => '3',
    'a4' => '4',
    'a5' => '5',
    'a6' => '6'
];
if (isset($arr[ $key ]))
    $arr = [ $key => $arr[ $key ] ] + $arr;

array(
    'a3' => '3',
    'a1' => '1',
    'a2' => '2',
    'a4' => '4',
    'a5' => '5',
    'a6' => '6'
)