Transparently flatten an array

Question

Reading this question Merge and group by several arrays i got the following idea: when working with multilevel arrays, with possibly repeating keys, it would be practical to

Answer 1

You can also write a simple traversal function:

function flatten($node, $fn, $keys = array()) {
    if (! is_array($node)) {
        $fn($node, $keys);
    } else {
        foreach ($node as $k => $v) {
            $new_keys   = $keys;
            $new_keys[] = $k;
            flatten($v, $fn, $new_keys);
        }
    }
}

$array = array( 
    0 => 'a', 
    1 => array('subA','subB',array(0 => 'subsubA', 1 => 'subsubB', 2 => array(0 => 'deepA', 1 => 'deepB'))), 
    2 => 'b', 
    3 => array('subA','subB','subC'), 
    4 => 'c' 
);
// will output: a subA subB subsubA subsubB deepA deepB b subA subB subC c 
flatten($array, function($v, $k) {
    echo $v . ' ';
});

If you don't want to call it each time with another function as a parameter, I've also written an adapter that will return an array:

function flatten_array($node) {
    $acc = array();
    flatten($node, function($node, $keys) use (&$acc) {
        $acc[implode('.', $keys)] = $node;
    });
    return $acc;
}

// will spit out the same output as that in Yoshi's answer:
foreach (flatten_array($array) as $k => $v) {
    echo $k .' => ' . $v . "\n";
}

Notes:

• array_walk_recursive cannot be used/is not the same thing, as it skips over the keys that hold an array
• I've written my examples with anonymous functions; if your PHP isn't new enough, you have to name the functions and call them with call_user_func.