Get an average of values every nth value in array

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

Why those two returns? Is that the rounded average of 1375398000 => int 350 and 1375398015 => int 357 with the key of 1375398000, and the rounded average of 1375398030 => int 354 and 1375398045 => int 353 with a key of 1375398030? Just trying to get the logic that you want straight in my head — Mark Baker
– Mark Baker, Commented Nov 15, 2013 at 14:51
thats correct @MarkBaker, I need to shorten the array so the data is at every 30 seconds whilst taking into account any values between the 30 seconds. — GSinghLDN
– GSinghLDN, Commented Nov 15, 2013 at 14:54
So there could be entries every 10 seconds, but you still need 30 second interval averages — Mark Baker
– Mark Baker, Commented Nov 15, 2013 at 14:59

Simon Márton · Accepted Answer · 2013-11-15 15:40:36Z

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;

answered Nov 15, 2013 at 15:40

Simon Márton

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