data x;
input id day timep results flag $;
cards;
1 1 0 23 .
1 1 1 43 X
1 1 2 29 .
1 1 3 14 .
2 1 0 17 .
2 1 1 32 .
2 1 2 54 X
2 1 3 59 .
;
run;
data before after;
set x;
by id;
retain found;
if first.id then call missing(found);
if flag='X' then found=1;
if not found then output before;
else if flag ne 'X' then output after;
drop found;
run;
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