/*<!-- AUTHOR DROPDOWN --> */
add_filter('relevanssi_hits_filter', 'rlv_gather_authors', 99);
function rlv_gather_authors($hits) {
    global $rlv_author_present;
    $rlv_author_present = array();
    foreach ( $hits[0] as $hit ) {
        $terms = get_the_terms( $hit->ID, 'author' );
        if (is_array($terms)) {
            foreach ( $terms as $term ) {
                $rlv_author_present[ $term->term_id ] = $term->name;
            }
        }
    }
    asort( $rlv_author_present );
    return $hits;
}
function rlv_author_dropdown() {
    global $rlv_author_present, $wp_query;

    if (!empty($wp_query->query_vars['author'])) {
        $url = esc_url(remove_query_arg('author'));
        echo "<p><a href='$url'>Remove author filter</a>.</p>";
    }
    else {
        $select = "<select class='select' id='rlv_author' name='rlv_author'><option value=''>Filter Results by Author</option>";
        foreach ( $rlv_author_present as $author_id => $author_name ) {
            $select .= "<option value='$author_id'>$author_name</option>";
        }
        $select .= "</select>";
        $url = esc_url(remove_query_arg('paged'));
        if (strpos($url, 'page') !== false) {
            $url = preg_replace('/page\/\d+\//', '', $url);
        }
        $select .= <<<EOH
        <script>
<!--
    var dropdown = document.getElementById("rlv_author");
    function onAuthorChange() {
        if ( dropdown.options[dropdown.selectedIndex].value > 0 ) {
            location.href = "$url"+"&author="+dropdown.options[dropdown.selectedIndex].value;
        }
    }
    dropdown.onchange = onAuthorChange;
-->
</script>
EOH;

        echo $select;
    }
}
 /*<!-- /AUTHOR DROPDOWN -->*/