Sample

        if(!empty($args['top-first'])):
            uasort($formatted, array($this, 'compare'));
        else:
            ksort($formatted);
        endif;
        return array('agents' => $formatted, 'dates' => $dates, 'totals' => $totals, 'colors' => $colors);
    }
    function compare($a, $b){
        if ($a['sales'] == $b['sales']) {
            return 0;
        }
        return ($a['sales'] > $b['sales']) ? -1 : 1;
    }