Copy value for certain rows grouped by person

[A_Halps]

Hi,

I am trying to go from:

SSN   TEST  

1          1       

2          4       

2          2       

3          2       

TO:

SSN   TEST   FLAG

1          1         .

2          4         1

2          2         1

3          2         .

So, I want to create a flag that if the test=4 then each flag for that specific person will be 1.

This is what I currently have, but it is not grouping it by person and is continuing down the entire list, which is not what i want.

data want;
set have;
by ssn;
if test=4 then flag=1;
retain flag;
run;

[PeterClemmensen]

So if TEST = 4 for any obs in a group, then flag = 1 for all obs in that group?

[A_Halps]

Yes. And I currently have it set up with 4 is the top because i sorted it by ssn and descending test (4 is the highest it goes).

[PeterClemmensen]

If so then do

data have;
input SSN TEST;
datalines;
1 1 
2 4 
2 2 
3 2 
;

data want;
   do _N_ = 1 by 1 until (last.ssn);
      set have;
	  by ssn;
	  if test = 4 then flag = 1;
   end;

   do _N_ = 1 to _N_;
      set have;
      output;
   end;
run;

[A_Halps]

What does "_N_ = 1 " do?

[PeterClemmensen · Accepted solution]

If you know that test = 4 is the first in each group, a simpler single-pass solution could be

data have;
input SSN TEST;
datalines;
1 1 
2 4 
2 2 
3 2 
;

data want;
   set have;
   by ssn;
   if first.ssn then flag = .;
   if test = 4 then flag = 1;
   retain flag;
run;