proc sort data=a out=b;
by x1;

data c;
set b;
if firstlist=1 then output  (first...我忘记怎么拼了  这样最简单 我觉得 尽管有些麻烦)
run;

data a;
input no x1 x2 x3 x4 x5;
cards;
1 16 21 7.5 1910 9
1 16 21 7.5 1910 9
1 21 26 7.8 1881 12
2 31 36 12.5 478 14
2 31 36 12.5 478 14
2 36 41 14.9 537 16
2 36 41 14.9 537 16
3 25 30 7.6 1552 11
3 25 30 7.6 1552 11
;
run;
data b;
set a;
by no x1;
if first.x1;
run;
proc print data=b noobs;
run;