php合并二维数组相同的key

Question

有个二维数组：$arr=array(array('num'=>5,'period'=>3),array('num'=>10,'period'=>3),array('num'=>15,'period'=>9));对period相同的值的数组，对num求和，怎么处理变成：$arr=array(array('num'=>15,'period'=>3),array('num'=>15,'period'=>9));

Answer 1

把@mot的答案补完优雅一下：
$arr=array(
array('num'=>5,'period'=>3),
array('num'=>10,'period'=>3),
array('num'=>15,'period'=>9)
);
$temp=array();
foreach($arras$item){
list($n,$p)=array_values($item);
$temp[$p]=array_key_exists($p,$temp)?$temp[$p]+$n:$n;
}
$arr=array();
foreach($tempas$p=>$n)
$arr[]=array('num'=>$n,'period'=>$p);
print_r($arr);
                            

Answer 2

$tmp=array();
foreach($arras$one)
{
if($tmp[$one['period']])
$tmp[$one['period']]=$tmp[$one['period']]+$one['num'];
else
$tmp[$one['period']]=$one['num'];
}
$arr=array();
foreach($tmpas$key=>$value)
$arr[]=array('num'=>$value,'period'=>$key);