<!-- Collection of code snippets by Arne Vajhøj -->
<!-- posted to eksperten.dk, usenet and other places (2002-now) -->
<?php
$input =
array (
        'a' =>
        array (
                'b1' =>
                array (
                        'c1' => 1,
                        'c2' => 2,
                        'c3' => 3,
                ),
                'b2' =>
                array (
                        'c' => 4,
                ),
        ),
);

$target = 
array (
        'a/b1/c1' => 1,
        'a/b1/c2' => 2,
        'a/b1/c3' => 3,
        'a/b2/c' => 4,
);

function dump($a) {
    foreach($a as $path => $value) {
        echo "$path => $value\r\n";
    }
}

function pathjoin_help($o, $elms, &$res) {
    if(is_int($o)) {
        $res[implode('/', $elms)] = $o;
    } else if(is_array($o)) {
        $elms[] = null;
        foreach($o as $pathelm => $value) {
            $elms[count($elms)-1] = $pathelm;
            pathjoin_help($value, $elms, $res);
        }
    } else {
        die("Houston we have a problem");
    }
}

function pathjoin($a) {
    $res = array();
    pathjoin_help($a, array(), $res);
    return $res;
}

$output = pathjoin($input);
dump($output);
dump($target);

print_r(
        pathjoin(
                array (
                        'a' =>
                        array (
                                'b1' =>
                                array (
                                        'c1' => '1',
                                        'c2' => 2,
                                        'c3' => 3,
                                ),
                                'b2' =>
                                array (
                                        'c' => 4,
                                ),
                        ),
                )
                )
        ); 
?>