Canvasjs divide sum with total row values per day

Question

I am working with canvajs ,I need to work with the daily ph value of a specific month.The json output below shows the time stamp converted to only date 12 and 21 of September

[{"ts":"12","ph":744},{"ts":"21","ph":200}]

Now, my problem is I wanted to divide ph with the overall number of rows. The 744 on the above json result is only the sum of the ph on a specific Month.

 $sumsep = 0;
    $sumjul = 0;
    $data_points = array();
    while($row = mysqli_fetch_array($result)){      
        $monthNum = date('m',strtotime($row['time_stamp']));
        $DayNum = date('d', strtotime($row['time_stamp']));     
        $dateObj   = DateTime::createFromFormat('!m', $monthNum);
        $monthName = $dateObj->format('F');
        if($monthNum == "8"){
            if (array_key_exists($DayNum, $data_points)) {
               $data_points[$DayNum]->ph += $row['ph'];
            }else{
$data_points[$DayNum]->ts = $DayNum;
$data_points[$DayNum]->ph = $sumsep;
$point = array("ts"=>date('d',strtotime($row['time_stamp'])),"ph" =>$row['ph']);         
      }}}}
    $jsonResult = json_encode(array_values($data_points));     
    echo $jsonResult;

I need to divide the 744 and 200 with the number of rows on the specific month.I hope anyone can help me out there.