- reset: documentation ( source)
- key: documentation ( source)
<?php
$array = array("person1" => array(0 => array('k1'=>'v1', 'k2'=>'v2'), 1 => array('k1'=>'v1', 'k2'=>'v2')), "person2" => array(0 => array('k1'=>'v1', 'k2'=>'v2'), 1 => array('k1'=>'v1', 'k2'=>'v2')));
$reset_key = reset($array);
$first_key = key($array);
echo $reset_key[0];