Turn flat array into nested array

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

because when I built the result array I wanted i used 1 as the value. It really doesn't matter what the value is though. I will change to int(3) to make it clearer — Mike
– Mike, Commented Sep 18, 2012 at 23:48

Explosion Pills · Accepted Answer · 2012-09-19 00:07:09Z

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).

edited Sep 19, 2012 at 0:07

answered Sep 18, 2012 at 23:49

Explosion Pills

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b.b3rn4rd · Accepted Answer · 2012-09-19 02:06:04Z

0

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
                                (
                                )

                        )

                )

        )

)

answered Sep 19, 2012 at 2:06

b.b3rn4rd

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