Realloc не может выделить память при использовании в цикле

Еще одна идея:

$ar = [
    'a' => [1,2,3],
    'b' => [4,5,6],
    'c' => [7,8,9]
];

$counts = array_map("count", $ar);
$total = array_product($counts);
$res = [];

$combinations = [];
$curCombs = $total;

foreach ($ar as $field => $vals) {
    $curCombs = $curCombs / $counts[$field];
    $combinations[$field] = $curCombs;
}

for ($i = 0; $i < $total; $i++) {
    foreach ($ar as $field => $vals) {
        $res[$i][$field] = $vals[($i / $combinations[$field]) % $counts[$field]];
    }
}

var_dump($res);