php dot string to tree

gistfile1.php

<?php

$map = array(
	'person.firstname' => 'John',
	'person.lastname' => 'Doe',
	'gender' => 'male',
	'some.arbitrary.structure.key' => 'smthng'
);

function tree($map) {
	$fn = function($carry, $key){
		return array($key => $carry);
	};
	$result = array();
	foreach($map as $key => $val) {
		$path = array_reverse(explode('.', $key));
		$result = array_merge_recursive($result, array_reduce($path, $fn, $val));
	}
	return $result;
}

$result = tree($map);

echo '<pre>';
print_r($result);
echo '</pre>';