Dynamic Array traversal in PHP

Question

I want to build a hierarchy from a one-dimensional array and can (almost) do so with a more or less hardcoded code. How can I make the code dynamic?

Perhaps with while(isset($array[$key])) { ... }? Or, with an extra function? Like this: $out = my_extra_traverse_function($array,$key);

function array_traverse($array,$key=NULL) {
    $out = (string) $key;
    $out = $array[$key] . "/" . $out;

    $key = $array[$key];
    $out = $array[$key] ? $array[$key] . "/" . $out : "";
    $key = $array[$key];
    $out = $array[$key] ? $array[$key] . "/" . $out : "";
    $key = $array[$key];
    $out = $array[$key] ? $array[$key] . "/" . $out : "";

    return $out;
}

$a = Array(102=>101, 103=>102, 105=>107, 109=>105, 111=>109, 104=>111);
echo array_traverse($a,104);

Output: 107/105/109/111/104

Answer 1

I THINK you want:

function array_traverse($array, $key = null) {
    $out = (string) $key;
    if (isset($array[$key])) {
        $out = array_traverse($array, $array[$key]) . '/' . $out;
    }
    return $out;
}

Or, for a non-recursive method:

function array_traverse($array, $key = null) {
    $out = (string) $key;
    while(isset($array[$key])) {
        $out = $array[$key] . '/' . $out;
        $key = $array[$key];
    }
    return $out;
}

Answer 2

Yes, I would say isset() is the way to go:

traverse($array, $value) {
    $result = array();
    while (isset($array[$value])) {
        array_unshift($result, $value);
        # or just $result[] = $value if you want to append
        # instead of prepending
        $value = $array[$value];
    }
    return $result;
    # or return implode('/', traverse(array(...))),
    # but I always prefer array return types in such cases:
    # they are much more flexible to the users of the function
}

# BTW: Using implode will avoid having an unnecessary
# leading/trailing delimiter (slash in this case)
echo implode('/', traverse(array(...)));