理解的是根据id和line分组,代码如下:
data aaa;
input id line x;
cards;
1 1 1
1 1 2
1 2 2
2 1 2
2 2 2
2 2 3
3 1 1
3 2 1
3 3 2
;
run;

proc sort data = aaa;
by id line x;
run;

data bbb;set aaa;
by id line;
if first.line then Y='Y';
run;

如果只是针对line分组,代码:
proc sort data = aaa;
by line x;
run;

data bbb;set aaa;
by line;
if first.line then Y='Y';
run;