----------------------- copy starting from the next line -----------------------

------------------ copy up to and including the previous line ------------------

我的要求是：将t002_psu_2_ 为缺失的数值，使用t002_psu_3_ 、t002_psu_4_或 t002_psu_5_   中非缺失的数值进行替换；将t002_psu_3_ 为缺失的数值，使用t002_psu_4_ 或 t002_psu_5_   中非缺失的数值进行替换；最终，得到如下结构的数据：
----------------------- copy starting from the next line -----------------------