二維陣列求和,,,針對鍵名數量不等的情況

求和陣列:
$data = array(
  '0' => array
      (
          'id' => 1518,
          'date' => 1495728000,
          'type' => 61,
          'content' => '{"2":2,"3":4,"4":6,"5":8}'
      ),

  '1' => array
      (
          'id' => 1519,
          'date' => 1495641600,
          'type' => 62,
          'content' => '{"1":3,"3":5,"2":5,"6":6}'
      ),
  '2' => array
      (
          'id' => 1519,
          'date' => 1495555200,
          'type' => 63,
          'content' => '{"7":219,"8":112,"9":268}'
      ),
  '3' => array
      (
          'id' => 1519,
          'date' => 1495468800,
          'type' => 64,
          'content' => '{"14":219,"16":112,"23":268,"18":268}'
      )    
  );

/**求和函式
*$n  求和天數
*$data  求和資料
*/
function sum($n,$data)
{
  $sum = $sum_tmp = array();
  foreach ($data as $key => $val) {
      // print_r($val);exit;
      $content = json_decode($val['content'],true);
      // print_r($content);exit;
      if ((($key + 1) % $n) != 0) {
          //非$n的倍數  一直累加
          foreach($content as $k=>$v){
            if(!isset($sum_tmp[$k])){
              $sum_tmp[$k] = $v;
            }else{
              $sum_tmp[$k] += $v;
            }
          }
          if (($key + 1) == count($data)) {
              $sum[$val['date']]['date'] = date('Y-m-d',($val['date']+($n-1)*86400)).'---'.date('Y-m-d',$val['date']);
              foreach($sum_tmp as $k=>$v){
                  $sum[$val['date']][$k] = $v;
              }
          }
      } elseif ((($key + 1) % $n) == 0) {
          //$n的倍數 縫$n求和
          foreach($content as $k=>$v){
            if(!isset($sum_tmp[$k])){
              $sum_tmp[$k] = $v;
            }else{
              $sum_tmp[$k] += $v;
            }
          }
          $sum[$val['date']]['date'] = date('Y-m-d',($val['date']+($n-1)*86400)).'--'.date('Y-m-d',$val['date']);
          foreach($sum_tmp as $k=>$v){
              $sum[$val['date']][$k] = $v;
          }
          unset($sum_tmp);
      }
  }
  return $sum;
}

print_r(sum(2,$data));    //注紅色部分為解決求和陣列之間單元數量不等的問題

列印結果為:

Array
(
    [1495641600] => Array
        (
            [date] => 2017-05-26--2017-05-25
            [2] => 7
            [3] => 9
            [4] => 6
            [5] => 8
            [1] => 3
            [6] => 6
        )

    [1495468800] => Array
        (
            [date] => 2017-05-24--2017-05-23
            [7] => 219
            [8] => 112
            [9] => 268
            [14] => 219
            [16] => 112
            [23] => 268
            [18] => 268
        )

)