gen birthweight=2 if chushengtizhong!=.
replace birthweight=1 if chushengtizhong<5
replace birthweight=3 if chushengtizhong>8 & chushengtizhong!=.
char birthweight [omited] 2

前三句是将出生体重分为三类，birthweight<5，birthweight=5~8，birthweight>8，最后一句这个char命令已经后面的omited是什么意思呢 初级高级教程并未找到详细讲解