This example demonstrates using the getDepth() method with a RecursiveArrayIterator.
<?php
$tree = array();
$tree[1][2][3] = 'lemon';
$tree[1][4] = 'melon';
$tree[2][3] = 'orange';
$tree[2][5] = 'grape';
$tree[3] = 'pineapple';
print_r($tree);
 
$arrayiter = new RecursiveArrayIterator($tree);
$iteriter = new RecursiveIteratorIterator($arrayiter);
 
foreach ($iteriter as $key => $value) {
 $d = $iteriter->getDepth();
 echo "depth=$d k=$key v=$value\n";
}
?>

The output of this would be:
Array
(
 [1] => Array
 (
 [2] => Array
 (
 [3] => lemon
 )
 [4] => melon
 )
 [2] => Array
 (
 [3] => orange
 [5] => grape
 )
 [3] => pineapple
)
depth=2 k=3 v=lemon
depth=1 k=4 v=melon
depth=1 k=3 v=orange
depth=1 k=5 v=grape
depth=0 k=3 v=pineapple