dynamic array key additions (sucky title, i know)

Question

precode: $keys = array('a', 'b', 'c', 'd'); $number = 10;

code: eval('$array[\''.implode('\'][\'',$keys).'\'] = $number;');

result:

Array (

[a] => Array
    (
        [b] => Array
            (
                [c] => Array
                    (
                        [d] => 10
                    )

            )

    )

)

problem: this is the exact result I want. Exactly! I have a list of keys and a number. The number should be set to the value of the keys array being used to generate child-based keys for a certain array (in this case called $array).

I DONT want to use eval though. I hate it. It's a hack and I want to write it proper, but after 8 hours (literally) of playing around with this, I've come to my end. A few resolutions I came up with produced this desired data set, but the nice thing about using eval us that it preserves the value of the array before hand. So it $array has some other values in it, it's not just going to overwrite them with my new keys/number. That's the part that gave me so much trouble.

Any help would be REALLY appreciate. Thanks dudes.

Answer 1

Please note that the code below (which you evaluate) will generate a warning, and will therefore not work on projects with error reporting up to the max:

$array = array();
$array['a']['b'] = 42; // $array['a'] is not an array... yet

Since you're using PHP 5, you can work with references to manipulate your array while traversing the branch of your tree that you wish to modify.

$current = & $array;

foreach ($keys as $key):

  if (!isset($current[$key]) || !is_array($current[$key]))
    $current[$key] = array();

  $current = & $current[$key];

endforeach;

$current = $value;

Edit: corrected for avoiding warnings and conflicts.

Answer 2

Here is a full code example showing how it would work. Whats important is that you use a reference to the array so you can modify it:

<?php
    $keys = array('a', 'b', 'c', 'd'); 
    $number = 10;

    $org_array = array(
        "a" => "string",
        "z" => array( "k" => false)
      );

    function write_to_array(&$array, $keys, $number){
      $key = array_shift($keys);
      if(!is_array($array[$key])) $array[$key] = array();
      if(!empty($keys)){
        write_to_array($array[$key], $keys, $number);
      } else {
        $array[$key] = $number;
      }
    }

    write_to_array($org_array, $keys, $number);

    print_r($org_array);
?>

Answer 3

function deepmagic($levels, $value)
{
    if(count($levels) > 0)
    {
        return array($levels[0] => deepmagic(array_slice($levels, 1),
            $value));
    }
    else
    {
        return $value;
    }
}

$a = deepmagic(Array('a', 'b', 'c', 'd'), 10);

var_dump($a);

Output:

array(1) {
  ["a"]=>
  array(1) {
    ["b"]=>
    array(1) {
      ["c"]=>
      array(1) {
        ["d"]=>
        int(10)
      }
    }
  }
}