How can I nest each item in an array within each other in PHP?

Question

If I have the following array:

[
  'foo',
  'bar',
  'baz' 
]

How can I get this output with PHP dynamically:

[
  'foo' => [
    'bar' => [
      'baz' => []
    ]
  ]
]

EDIT

I ended up achieving it by building the array backward and keeping track of the last key, but I would be interested in a cleaner recursive approach:

$arr = ['foo', 'bar', 'baz'];
$new_arr = [];
$last_key = null;

foreach ( array_reverse( $arr ) as $item ) {
    if ( $last_key ) {
        $new_arr[ $item ] = $new_arr;
        unset( $new_arr[ $last_key ] );
        $last_key = $item;
    } else {
        $new_arr[ $item ] = [];
        $last_key = $item; 
    }
}

Answer 1

If you want to use a foreach you don't have to unset or use an if/else.

You could reverse the $arr, and wrap the $new_arr (the result) inside a new array for each iteration using the value of $arr as the key.

$arr = [
    'foo',
    'bar',
    'baz'
];

$new_arr = [];

foreach(array_reverse($arr) as $v) {
    $new_arr = [$v => $new_arr];
}

print_r($new_arr);

See a PHP demo.

Output

Array
(
    [foo] => Array
        (
            [bar] => Array
                (
                    [baz] => Array
                        (
                        )

                )

        )

)