How can I loop through an array while averaging the values of one element and only keep the newly averaged field in PHP?

Question

I have database that contains scores which are stored daily. I want to average each months scores for each user. So far I have this:

DB structure:

id | name    | tscore            | added 

int| string  | float(100 or less)| date(2014-01-01 16:34:22)

Code:

while($row = mysql_fetch_assoc($getChartData)){ // Data from MySQL
    $added_date = explode(' ',$row['added']); // Date formate 2014-01-01 16:34:22
    $chartData[] = array(
        'id'     => $row['name'],
        'tscore' => $row['tscore'],
        'added'  => $added_date[0] // Here I take the month only
    );
}
if($_POST['range'] == 'month'){
    foreach($chartData as $key => $value){
        $added = explode('-',$chartData[$key]['added']);
        $count = 1;
        foreach($chartData as $key2 => $value2){
            $added2 = explode('-',$chartData[$key2]['added']);
            if($chartData[$key]['id'] === $chartData[$key2]['id'] && $added[1] === $added2[1]){ // if user is the same and the month is the same, add the scores together, increment counter, and unset 2nd instance
                $chartData[$key]['tscore'] = ((float)$chartData[$key]['tscore'] + (float)$chartData[$key2]['tscore']);
                $count++;
                unset($chartData[$key2]);
            }     
        }
        $chartData[$key]['tscore'] = ($chartData[$key]['tscore']/$count); // Average all the scores for the month.
    }
}

The problem is this method is deleting all the elements of the $chartData array. What can I try to resolve this?

Answer 1

You should try to solve it with MySQL. Try something like this (replace 'your_scores_table' with your table name):

SELECT
    Score.name, 
    AVG(Score.tscore) AS `avg`,
    CONCAT(YEAR(Score.added), '-', MONTH(Score.added)) AS `year_month`
FROM 
    your_scores_table AS Score
GROUP BY 
    Score.name ASC, 
    YEAR(Score.added) DESC, 
    MONTH(Score.added) DESC
;

Answer 2

Your logic is wrong. You are looping through the same array twice. Which means that the following if will always evaluate to true which means that array item will always get unset

//This will always be true
if($chartData[$key]['id'] === $chartData[$key2]['id'] && $added[1] === $added2[1]){

It may be simpler for you to create another array where you keep your scores. Something like

$aScores = array();
$count = 1;
foreach($chartData as $key => $value){

    //Add score to a different array
    $aScores[$value['name']]['tscore'] = (($aScores[$value['name']]['tscore'] + $value['tscore']) / $count);

    $count++;
}

Also I would look into the MySQL AVG function. You could use that to save you having to do it in PHP