Alter (or remove) querystring keys from a root-relative URI

alterQueryString.php

<?php

/**
 * Alter (or remove) querystring keys from a root-relative URI.
 * @param array $values associative array (see http_build_query). Use null value to remove keys
 * @param string $uri if not given, $_SERVER['REQUEST_URI'] will be used
 * @return string
 */
function alterQueryString($values = array(), $uri = null) {
    $parts = parse_url($uri ? $uri : $_SERVER['REQUEST_URI']);
    $query = array();
    if (isset($parts['query'])) {
        parse_str($parts['query'], $query);
    }
    $query = array_merge($query, $values);
    $qs = http_build_query($query, null, '&');
    return $parts['path'] . ($qs ? "?$qs" : '');
}

// /hello         => /hello?sort=title
// /hello?abc=123 => /hello?abc=123&sort=title
$uri = alterQueryString(array('sort' => 'title'));

// /hello?abc=123            => /hello
// /hello?abc=123&sort=title => /hello?sort=title
$uri = alterQueryString(array('abc' => null));