二维数组中一维的一个 【键】作为二维【键的值】如何变换？

Question

这是初始数组：

$arr = array(
        'CC'=>array(
            'recharge_status'=> 1,
            'withdraw_status'=> 1,
            'trade_status'=> 1,
            'withdraw_fee'=> 0.01,
            'precision'=> 7,
        ),
        'DD'=>array(
            'recharge_status'=> 2,
            'withdraw_status'=> 2,
            'trade_status'=> 2,
            'withdraw_fee'=> 0.02,
            'precision'=> 8,
        ),
        'EE'=>array(
            'recharge_status'=> 3,
            'withdraw_status'=> 3,
            'trade_status'=> 3,
            'withdraw_fee'=> 0.03,
            'precision'=> 9,
        ),
    );

期望结果是：

$newarr = array(
        0=>array(
            'asset_code'=> 'CC',
            'recharge_status'=> 1,
            'withdraw_status'=> 1,
            'trade_status'=> 1,
            'withdraw_fee'=> 0.01,
            'precision'=> 7,
        ),
        1=>array(
            'asset_code'=> 'DD',
            'recharge_status'=> 2,
            'withdraw_status'=> 2,
            'trade_status'=> 2,
            'withdraw_fee'=> 0.02,
            'precision'=> 8,
        ),
        2=>array(
            'asset_code'=> 'EE',
            'recharge_status'=> 3,
            'withdraw_status'=> 3,
            'trade_status'=> 3,
            'withdraw_fee'=> 0.03,
            'precision'=> 9,
        ),
    );