You don't need recursion. A single loop is fine with references.
<?php
//array to iterate
$array = array('level1', 'level2', 'level3');
//contains our entire array
$out = array();
//temp variable to store references as we go down.
$tmp = &$out;
//get the last value off the array
$last = array_pop($array);
//loop over the array
foreach($array as $level){
//make an array under the current level
$tmp[$level] = array();
//assign tmp to the new level
$tmp = &$tmp[$level];
}
//assign the last key as the value under the last key
$tmp = $last;
//display output
print_r($out);
example: http://codepad.viper-7.com/zATfyo
And without references, working in reverse:
<?php
//array to iterate
$array = array('level1', 'level2', 'level3');
//get the last value off the array
$out = array_pop($array);
//flip the array backwards
$array = array_reverse($array);
//loop over the array
foreach($array as $level){
$out = array($level=>$out);
}
//display output
print_r($out);
Example: http://codepad.viper-7.com/fgxeHO