Turn flat array into nested array - php

Question

Just working on something and can't find a simple solution to this problem without just looping through the array with a foreach. Does anyone have a simple solution for this
I want to turn this
&array(4) {
["a"]=>int(0)
["b"]=>int(1)
["c"]=>int(2)
["d"]=>int(3)
}
Into this
array(1) {
["a"]=>
array(1) {
[0]=>
array(1) {
["b"]=>
array(1) {
[0]=>
array(1) {
["c"]=>
array(1) {
[0]=>
array(1) {
["d"]=> int(1) //this value does not matter
}
}
}
}
}
}
}
The values don't matter at all I just need the keys to run against a array_intersect_key_recursive function that I have.
EDIT : The array has changed after testing it needs to be nested as an array of an array

Answer 1

I don't know how this could possibly end up helping you, but it was a fun exercise nonetheless.
$newArray = array();
$last = &$newArray;
$array = array_reverse(array_keys($array));
while ($item = array_pop($array)) {
if (!is_array($last)) {
$last = array();
}
$last[$item] = array(array());
$last = &$last[$item][0];
}
NOTE: I made this answer with the int(1). You said the value is not important so I'm not going to bother changing it for now, but you would have to do a bit more work if the value was important (probably something like get the value from the original array with $item as the key).

Answer 2

Another approach using recursion:
function toNestedArray(array $array, $index = 0) {
$return = array();
if ($index < count($array)) {
$return[$array[$index]] = toNestedArray($array, ++$index);
}
return $return;
}
Usage Example:
$flatArray = array('a' => 1, 'b' => 2, 'c' => 3, 'd' => 4);
$nestedArray = toNestedArray(array_keys($flatArray));
print_r($nestedArray);
Output:
Array
(
[a] => Array
(
[b] => Array
(
[c] => Array
(
[d] => Array
(
)
)
)
)
)