Dynamically creating/inserting into an associative array in PHP

Question

I'm trying to build an associative array in PHP dynamically, and not quite getting my strategy right. Basically, I want to insert a value at a certain depth in the array structure, for instance:

$array['first']['second']['third'] = $val;

Now, the thing is, I'm not sure if that depth is available, and if it isn't, I want to create the keys (and arrays) for each level, and finally insert the value at the correct level.

Since I'm doing this quite a lot in my code, I grew tired of doing a whole bunch of "array_key_exists", so I wanted to do a function that builds the array for me, given a list of the level keys. Any help on a good strategy for this is appreciated. I'm sure there is a pretty simple way, I'm just not getting it...

Answer 1

php doesn't blame you if you do it just so

$array['first']['second']['third'] = $val;
print_r($array);

if you don't want your keys to be hard coded, here's a flexible solution

/// locate or create element by $path and set its value to $value
/// $path is either an array of keys, or a delimited string
function array_set(&$a, $path, $value) {
    if(!is_array($path))
        $path = explode($path[0], substr($path, 1));
    $key = array_pop($path);
    foreach($path as $k) {
        if(!isset($a[$k]))
            $a[$k] = array();
        $a = &$a[$k];
    }
    $a[$key ? $key : count($a)] = $value;
}

// example:
$x = array();

array_set($x, "/foo/bar/baz", 123);
array_set($x, "/foo/bar/quux", 456);
array_set($x, array('foo', 'bah'), 789);

Answer 2

That's tricky, you'd need to work with references (or with recursion, but I chose references here):

# Provide as many arguments as you like:
# createNestedArray($array, 'key1', 'key2', etc.)
function createNestedArray(&$array) {
    $arrayCopy = &$array;
    $args = func_get_args();
    array_shift($args);
    while (($key = array_shift($args)) !== false) {
        $arrayCopy[$key] = array();
        $arrayCopy = &$arrayCopy[$key];
    }
}

Answer 3

Create a function like:

function insert_into(&$array, array $keys, $value) {
     $last = array_pop($keys);       

     foreach($keys as $key) {
          if(!array_key_exists($key, $array) || 
              array_key_exists($key, $array) && !is_array($array[$key])) {
                  $array[$key] = array();

          }
          $array = &$array[$key];
     }
     $array[$last] = $value;
}

Usage:

$a = array();
insert_into($a, array('a', 'b', 'c'), 1);
print_r($a);

Ouput:

Array
(
    [a] => Array
        (
            [b] => Array
                (
                    [c] => 1
                )

        )

)