public function get_sort_arrows(array $extrafields = array()) {
        global $OUTPUT, $CFG;
        $arrows = array();

        $strsortasc   = $this->get_lang_string('sortasc', 'grades');
        $strsortdesc  = $this->get_lang_string('sortdesc', 'grades');
        $iconasc = $OUTPUT->pix_icon('t/sort_asc', $strsortasc, '', array('class' => 'iconsmall sorticon'));
        $icondesc = $OUTPUT->pix_icon('t/sort_desc', $strsortdesc, '', array('class' => 'iconsmall sorticon'));

        // Sourced from tablelib.php
        // Check the full name display for sortable fields.
        if (has_capability('moodle/site:viewfullnames', $this->context)) {
            $nameformat = $CFG->alternativefullnameformat;
        } else {
            $nameformat = $CFG->fullnamedisplay;
        }

        if ($nameformat == 'language') {
            $nameformat = get_string('fullnamedisplay');
        }

        $arrows['studentname'] = '';
        $requirednames = order_in_string(get_all_user_name_fields(), $nameformat);
        if (!empty($requirednames)) {
            foreach ($requirednames as $name) {
                $arrows['studentname'] .= html_writer::link(
                    new moodle_url($this->baseurl, array('sortitemid' => $name)), $this->get_lang_string($name)
                );
                if ($this->sortitemid == $name) {
                    $arrows['studentname'] .= $this->sortorder == 'ASC' ? $iconasc : $icondesc;
                }
                $arrows['studentname'] .= ' / ';
            }

            $arrows['studentname'] = substr($arrows['studentname'], 0, -3);
        }

        foreach ($extrafields as $field) {
            $fieldlink = html_writer::link(new moodle_url($this->baseurl,
                    array('sortitemid'=>$field)), get_user_field_name($field));
            $arrows[$field] = $fieldlink;

            if ($field == $this->sortitemid) {
                if ($this->sortorder == 'ASC') {
                    $arrows[$field] .= $iconasc;
                } else {
                    $arrows[$field] .= $icondesc;
                }
            }
        }

        return $arrows;
    }