set the three first observations to missing by id

[sasphd]

Hello, 

I want to set three first observations to missing by id

Have 

id   mret

1     8

1    5

1   6

1   9

2   63

2    95

2  6

2   8

want 

id   mret

1     .

1    .

1   .

1   9

2   .

2    .

2  .

2   8

[PeterClemmensen · Accepted solution]

Try this

data have;
input id mret;
datalines;
1 8
1 5
1 6
1 9
2 63
2 95
2 6
2 8
;

data want(drop = c);
   set have;
   by id;
   if first.id then c = 0;
   c + 1;
   if c le 3 then mret = .;
run;