Access an array value based on a formatted keypath string

Check parse_str():

parse_str('set[0][p1]', $AR);

Oh, you want to access the index of the array... Here is my take:

getValue($AR, array('set', 0, 'p1'));

Or if you really must use the original string representation:

parse_str('set[0][p1]', $keys);
getValue($AR, $keys);

Disclaimer: I haven't tested this, you might need to use array_keys() somewhere.

And the helper function:

function getValue($array, $key, $default = false)
{
    if (is_array($array) === true)
    {
        settype($key, 'array');

        foreach ($key as $value)
        {
            if (array_key_exists($value, $array) === false)
            {
                return $default;
            }

            $array = $array[$value];
        }

        return $array;
    }

    return $default;
}

I would avoid regexing your way into this problem.

My try, which should be able to deal with an arbitrary amount of []s in the string:

To split the string you can use preg_split.

$parts = preg_split('%\[?(\w+)\]?%', $string, -1, PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY);

(More) complete code:

function get_value($string, $array) {
    $parts = preg_split('%\[?(\w+)\]?%', $string, -1, PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY);

    foreach($parts as $part) {
        $array = $array[$part];
    }

    return $array;
}

$array = array('set'=>array(array('p1'=>'foo')));
$string = "set[0][p1]";

echo get_value($string, $array); // echoes 'foo'

I leave the error handling to you ;)

Perhaps this is crazy, but have you considered extract? It may not be the fastest solution, but it has the novelty of needing minimal code.

extract( $AR );
$target = eval("\$set[0]['p1']");

The major difference (as far as input is concerned) is that you would need to pre-pend '$' to the string, and make sure that the brackets have quote marks inside.

The major benefit is that it becomes extraordinarily obvious what you're trying to accomplish, and you're using two native PHP functions. Both of these mean that the solution would be far more "readable" by those unfamiliar with your system.

Oh, and you're only using two lines of code.

You need something like. I'm not 100% about the "[" and "]" brackets as I've never had to run a regex on them before... if it's wrong can someone correct me??

foreach(preg_split('/[\[\]]/', "set[0][p1]") as $aValue) {
    $AR[$aValue[0]][$aValue[1]][$aValue[2]] = '?';
}