How to calculate geometric mean with big list of numbers up to four digits?

Question

Basic calculation of geometric mean is not that difficult, but I found myself hitting INF because list of numbers is big, up to 10k. So I tried to take a log of the numbers and exponentiate later, but still I got INF.

Next step was to chunk array of numbers, which seems good, but now I have a problem that if there is a reminder of the chunked array, result will be wrong. Is there any solution on this road, or would you prefer some other method of calculating geometric mean?

# testing with small number set
$a = array(13, 18, 13, 14, 13, 16, 14, 21, 13);
# number set will splice uneven with 2, thus giving wrong answer?
echo geometric_mean($a, 2);
echo " wrong<br />";

# number set will chunk evenly to 3 parts, thus giving right answer
echo geometric_mean($a, 3);
echo " correct<br />";

# straight way without splitting
echo _geometric_mean($a);
echo " correct<br />";

function geometric_mean($a, $size = 20) {
    $a = array_chunk($a, $size);
    foreach ($a as $b) {
        # finding, if there is a reminder after split of an array
        $c = count($b);
        if ($c < $size) {
            for ($i=$c; $i<$size; $i++) {
                # adding last mean to the array, but it's not good
                # adding 14.789726414533 would be ok...
                $b[] = $m;
            }
        }

        $m = _geometric_mean($b);
        $d[] = $m;
    }
    # recursive call if array size is bigger
    if (count($d) > $size) {
        geometric_mean($d, $size);
    }
    return _geometric_mean($d);
}
# basic function to get geometric mean
function _geometric_mean($a) {
    return pow(array_product($a), 1 / count($a));
}

Answer 1

Solution inspired found from: http://en.wikipedia.org/wiki/Geometric_mean#Relationship_with_arithmetic_mean_of_logarithms brought here by @ragol:

function geometric_mean($a) {
    array_walk($a, function (&$i) {
        $i = log($i);
    });
    return exp(array_sum($a)/count($a));
}

I'm not sure about efficiency but it works well on my app, no need for array splicing, recurring functions calls, and still no more INF.

Answer 2

That error means the number is too large for memory. Maybe the problem arises when you try to echo it. I'm not really sure. Try using this function:

is_infinite()