public function set_fields($fields, $output) {
        $this->fields = $fields;
        $this->head = array();
        $this->colclasses = array();
        $this->align = array();
        $url = $this->manager->get_moodlepage()->url;

        if (!empty($this->bulkoperations)) {
            // If there are bulk operations add a column for checkboxes.
            $this->head[] = '';
            $this->colclasses[] = 'field col_bulkops';
        }

        foreach ($fields as $name => $label) {
            $newlabel = '';
            if (is_array($label)) {
                $bits = array();
                foreach ($label as $n => $l) {
                    if ($l === false) {
                        continue;
                    }
                    if (!in_array($n, self::$sortablefields)) {
                        $bits[] = $l;
                    } else {
                        $sorturl = new moodle_url($url, array(self::SORTVAR => $n, self::SORTDIRECTIONVAR => $this->get_field_sort_direction($n)));
                        $link = html_writer::link($sorturl, $fields[$name][$n]);
                        if ($this->sort == $n) {
                            $link .= $this->get_direction_icon($output, $n);
                        }
                        $bits[] = html_writer::tag('span', $link, array('class'=>'subheading_'.$n));

                    }
                }
                $newlabel = join(' / ', $bits);
            } else {
                if (!in_array($name, self::$sortablefields)) {
                    $newlabel = $label;
                } else {
                    $sorturl = new moodle_url($url, array(self::SORTVAR => $name, self::SORTDIRECTIONVAR => $this->get_field_sort_direction($name)));
                    $newlabel  = html_writer::link($sorturl, $fields[$name]);
                    if ($this->sort == $name) {
                        $newlabel .= $this->get_direction_icon($output, $name);
                    }
                }
            }
            $this->head[] = $newlabel;
            $this->colclasses[] = 'field col_'.$name;
        }
    }