WordPress - Modifying URL's Query String, The Easy Way

gistfile1.php

/**
 * Modify URL's query string
 * 
 * @param string url to be modified
 * @param array of query strings
 * 
 * @return string of modified url
 */
function fr_modify_url( $url = '', $query_string_args = array() ){

    // Parse url to get query strings
    $parsed_url = parse_url( $url );

    if( isset( $parsed_url['query'] ) ){
        parse_str( $parsed_url['query'], $query_strings_default );
    } else {
        $query_strings_default = array();
    }

    // Parse the default query strings against the given one
    $query_strings = wp_parse_args( $query_string_args, $query_strings_default );

    $url = $parsed_url['scheme'] . '://' . $parsed_url['host'];

    if( isset( $parsed_url['path'] ) ){
        $url .= $parsed_url['path'];        
    }

    $url .= '?' . build_query( $query_strings );

    return $url;
}