获取数组中每第n个值的平均值

Question

I have the following array with they keys being unix timestamps, how can I get the average vlaue for example at an interval of every 30 seconds in a new array with the key being the 30 second interval?

array (size=61)
1375398000 => int 350
1375398015 => int 357
1375398030 => int 354
1375398045 => int 353
1375398060 => int 361
// and so on...

The desired output should be

1375398000 => int 353
1375398030 => int 354

I have tried some logic with using key($array) to get the first value but I cant figure out if this is working correctly inside a foreach loop.

My logic so far

     while($a <= $end){

    $chartData[$a] = $array[$a] //do the average here - current($array) / count($array);

}

I dont know how to get the next set of the keys and values to be used

Answer 1

I'd do this, I'm sure this is not the most elegant, but it gets the job done.

// Make sure the array is in the correct order
ksort($charData);

// This will be our new array
$tmp = array();

$interval = 30;

// Set the array's pointer to the first element
reset($charData); 
$last_timestamp = key($charData);

$total = 0;
$count = 0;

foreach ($charData as $timestamp => $value) {
    $total += $value;
    $count++;

    // If the current timestamp is newer 
    // than 30secs (or any interval set) we record the value
    if($timestamp - $last_timestamp >= $interval) {
        // Calculate the avg
        $tmp[$last_timestamp] = $total / $count;

        // Reset our helper vars
        $last_timestamp = $timestamp;
        $total = 0;
        $count = 0;
    }
}

$charData = $tmp;