如何將同一天的筆數相加？印成正確的json

Question

這是查詢結果

這是php查詢代碼

SELECT
FROM_UNIXTIME(add_time, '%Y-%m-%d') as add_time,
count(view_id) as viewTime
FROM `view`
GROUP BY `add_time`

這是整個php代碼

header('Content-type: application/json');
    $chartData = $pdo->query(
      "SELECT
FROM_UNIXTIME(add_time, '%Y-%m-%d') as add_time,
count(view_id) as viewTime
FROM `view`
GROUP BY `add_time` "
    );

    $data = array();
    $key = 0;
    foreach ($chartData as $item){
      $data[$key] = array(
        'date' => $item['add_time'],
        'number' => $item['viewTime']
      );

      $key++;
    }
    echo json_encode($data);

打印結果

[{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"},{"date":"2018-08-16","number":"1"}.............

右邊的 viewTime 都是一筆數據
但我想實現的是
日期重複只要顯示一個
但是同一個日期的數字都相加
這能怎麼實現？
我要在後端打印出這樣的json
可以的話附帶一下原理 感謝大神

Answer 1

$data = array();
foreach ($chartData as $item) {
  if (isset($data[$item['add_time']])) {
    $data[$item['add_time']]['number'] += $item['viewTime'];
  } else {
    $data[$item['add_time']] = array(
      'date' => $item['add_time'],
      'number' => $item['viewTime']
    );
  }
}
$data = array_values($data);
echo json_encode($data);