stata小白请教循环语句问题~~这是我正在做的上市公司2008至2018年分季度ROA和ROE数据，数据库中给出了A合并报表 B母公司报表两种报表类型，因为有一些公司只有合并报表，有一些公司只有母公司报表，还有一些两种报表类型都有列出但其中却夹杂着缺失值，我用bysort id bsdt (typrep): gen no=_N对每家公司分季度报表分组统计组数数，想要达到如果no==1就保留，如果no==2如果该家公司该时间段的A合并报表不为缺失值的则保留A，否则保留B，但是因为刚刚开始学习stata，不知道怎么用循环程序表达出来~~
clear
input long id str1 typrep str3 indu float(roa roe bsdt no)
1 "A" "J66" .008948 .294976 17622 1
1 "A" "J66"  .00971 .297848 17713 1
1 "A" "J66" .010469 .306175 17805 1
1 "A" "J66" .001485 .041761 17897 1
1 "A" "J66" .001572 .047049 17987 1
1 "A" "J66"  .00159 .044751 18078 1
1 "A" "J66" .001877 .049887 18170 1
1 "A" "J66" .009472 .272887 18262 1
1 "A" "J66" .009611 .280066 18352 1
1 "A" "J66"  .00987 .237663 18443 1
1 "A" "J66" .009968 .239194 18535 1
1 "A" "J66" .009557 .234177 18627 1
1 "A" "J66" .009959 .244847 18717 1
1 "A" "J66" .010813 .232814 18808 1
1 "A" "J66" .009876 .179041 18900 2
1 "B" "J66"       .       . 18900 2
1 "A" "J66" .010467 .191392 18992 2
1 "B" "J66"       .       . 18992 2
1 "A" "J66" .010557 .199879 19083 2
1 "B" "J66"       .       . 19083 2
1 "A" "J66" .010696 .212389 19174 2
1 "B" "J66"       .       . 19174 2
1 "A" "J66" .009678 .169366 19266 2
1 "B" "J66" .011339 .180627 19266 2
1 "A" "J66" .009433 .168696 19358 2
1 "B" "J66" .011374  .18803 19358 2
1 "A" "J66" .008558  .16223 19448 1
1 "A" "J66" .008544 .165404 19539 1
1 "A" "J66" .008917 .168262 19631 1
1 "A" "J66" .008708 .154724 19723 1
1 "A" "J66" .008544 .162051 19813 1
1 "A" "J66" .008968  .16728 19904 1
1 "A" "J66" .009615 .173509 19996 1
1 "A" "J66" .009711 .162959 20088 1
1 "A" "J66" .009258 .160446 20178 1
1 "A" "J66" .009057 .156832 20269 1
1 "A" "J66" .009212 .153929 20361 1
1 "A" "J66" .009317  .14953 20453 1
1 "A" "J66" .008954 .137674 20544 1
1 "A" "J66" .008404 .131777 20635 1
1 "A" "J66" .008476 .128567 20727 1
1 "A" "J66" .008277 .124283 20819 1
1 "A" "J66" .007992 .114984 20909 1
1 "A" "J66" .007759 .113411 21000 1
1 "A" "J66"  .00777 .110645 21092 1
1 "A" "J66" .007478 .109324 21184 1
1 "A" "J66"  .00743 .109341 21274 1
1 "A" "J66" .007433 .109223 21365 1
1 "A" "J66" .007548 .108051 21457 1
2 "A" "K70" .069677 .203744 17622 2
2 "B" "K70" .042736 .090677 17622 2
2 "A" "K70" .066639 .215437 17713 2
2 "B" "K70" .088329 .181697 17713 2
2 "A" "K70" .054147 .176788 17805 2
2 "B" "K70" .075659 .152047 17805 2
2 "A" "K70" .042309 .127577 17897 2
2 "B" "K70" .029583 .060592 17897 2
2 "A" "K70" .041462 .127285 17987 2
2 "B" "K70" .021388 .051209 17987 2
2 "A" "K70"  .04612 .139986 18078 2
2 "B" "K70" .044706 .091956 18078 2
2 "A" "K70" .045229 .143293 18170 2
2 "B" "K70" .038701 .084186 18170 2
2 "A" "K70" .050069 .152683 18262 2
2 "B" "K70" .048002  .10401 18262 2
2 "A" "K70"  .04917   .1542 18352 2
2 "B" "K70" .046449 .108543 18352 2
2 "A" "K70" .045543 .143876 18443 2
2 "B" "K70" .045746 .097245 18443 2
2 "A" "K70" .041493 .143634 18535 2
2 "B" "K70" .045946 .106691 18535 2
2 "A" "K70" .050048 .176802 18627 2
2 "B" "K70" .042242 .101033 18627 2
2 "A" "K70" .046142 .171047 18717 2
2 "B" "K70" .041855 .103127 18717 2
2 "A" "K70" .042381 .168155 18808 2
2 "B" "K70" .057299 .138141 18808 2
2 "A" "K70" .038716 .167514 18900 2
2 "B" "K70" .052522  .13501 18900 2
2 "A" "K70" .045325 .189507 18992 2
2 "B" "K70" .049637 .130152 18992 2
2 "A" "K70" .043753 .190662 19083 2
2 "B" "K70" .046638 .125318 19083 2
2 "A" "K70" .043569 .201856 19174 2
2 "B" "K70" .049879 .134584 19174 2
2 "A" "K70" .043232 .207927 19266 2
2 "B" "K70" .046948 .128788 19266 2
2 "A" "K70" .046407 .208875 19358 2
2 "B" "K70"  .05144 .149999 19358 2
2 "A" "K70"  .04372 .207112 19448 2
2 "B" "K70" .047312 .147248 19448 2
2 "A" "K70" .043174 .208525 19539 2
2 "B" "K70" .061505  .18636 19539 2
2 "A" "K70" .042016 .204733 19631 2
2 "B" "K70" .057601 .186744 19631 2
2 "A" "K70" .042651 .195093 19723 2
2 "B" "K70" .053727 .183121 19723 2
2 "A" "K70" .039751 .194729 19813 2
2 "B" "K70" .053645  .19522 19813 2
2 "A" "K70" .039516  .19046 19904 2
end
format %td bsdt
[/CODE]