二维数组a-z排序

/**
 * 将数组按字母A-Z排序
 * @return [type] [description]
 */
public function chartSort($user){
    foreach ($user as $k => &$v) {
        $v['chart']=$v['initial'];
    }
    $data=[];
    foreach ($user as $k => $v) {
        if ( empty( $data[ $v['chart'] ] ) ) {
            $data[ $v['chart'] ]=[];
        }
        $data[ $v['chart'] ][]=$v;
    }
    ksort($data);
    return $data;
}

temp是个二维数组。其中initial是这个数组里面的首字母