php二维数组处理

Question

$arr=array(array('amount'=>100,'date'=>'2014-03-29'),array('amount'=>120,'date'=>'2014-03-30'),array('amount'=>200,'date'=>'2014-03-31'));怎么转化成以日期为准，amount为之前amount的和？$arr=array(array('amount'=>100,'date'=>'2014-03-29'),array('amount'=>220,'date'=>'2014-03-30'),array('amount'=>420,'date'=>'2014-03-31'));

Answer 1

functionsd($a,$b){if($a['date']==$b['date'])return0;return$a['date']>$b['date']?1:-1;
usort($arr,'sd');
$amount=0;
foreach($arras&$item){
$amount+=$item['amount'];
$item['amount']=$amount;
}