Recursive array_search

You can change your recursive function like this, which should give you the solution:

function recursive_array_search($needle, $haystack, $currentKey = '') {
    foreach($haystack as $key=>$value) {
        if (is_array($value)) {
            $nextKey = recursive_array_search($needle,$value, $currentKey . '[' . $key . ']');
            if ($nextKey) {
                return $nextKey;
            }
        }
        else if($value==$needle) {
            return is_numeric($key) ? $currentKey . '[' .$key . ']' : $currentKey . '["' .$key . '"]';
        }
    }
    return false;
}

This will result in

[1][1][0]["CategoryID"]

Since CategoryID is also a key in your multidimensional array.

If you don't want this, you can adapt the function to

function recursive_array_search($needle, $haystack, $currentKey = '') {
    foreach($haystack as $key=>$value) {
        if (is_array($value)) {
            $nextKey = recursive_array_search($needle,$value, $currentKey . '[' . $key . ']');
            if ($nextKey) {
                return $nextKey;
            }
        }
        else if($value==$needle) {
            return is_numeric($key) ? $currentKey . '[' .$key . ']' : $currentKey;
        }
    }
    return false;
}

You are ignoring the returned value of your inner call to recursive_array_search. Don't do that.

/*
 * Searches for $needle in the multidimensional array $haystack.
 *
 * @param mixed $needle The item to search for
 * @param array $haystack The array to search
 * @return array|bool The indices of $needle in $haystack across the
 *  various dimensions. FALSE if $needle was not found.
 */
function recursive_array_search($needle,$haystack) {
    foreach($haystack as $key=>$value) {
        if($needle===$value) {
            return array($key);
        } else if (is_array($value) && $subkey = recursive_array_search($needle,$value)) {
            array_unshift($subkey, $key);
            return $subkey;
        }
    }
}