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, ), );