How to calulate different between first visit and las visit date in same IDin

[Bksong]

how to calulate follow up years?

ID First visit(SAS date). Last visit(SAS date)
Id firstvisit lastvisit
01 5543

01 11234

02 5436

02 8895
Numbers are SAS date.

How to clalulate lastvisit- firstvisit?
It's difficult to calculate between first visit and last visit since located in different row.

How can make code correctly??


BK.

[Bksong]

5543 is first visit
11234 is last visit
5436 is first visit
8895 is last visit

[novinosrin]

HI @Bksong  Since you mentioned first and last visit and that your visit dates are nicely sorted in ascending order within a given ID, all you need in my opinion is range function either in SQL, Proc means/summary

data have;
input Id $ visit;
format visit date9.;
cards;
01 5543
01 11234
02 5436
02 8895
;

proc sql;
 create table want as 
 select id, range(visit) as diff
 from have
 group by id;
quit;

[Bksong]

If visit date located in different calumn, how to make code?

[novinosrin]

Can you please post your "input" sample just like I posted the sample data have; and your expected output? plz

[Bksong]

idnumber first_date last_date
00001 5534
00001 . . . . . 10342
00002 4567
00002
00002 . . . . . 7800


Output
Idnumber first_date last_date followup_date
00001 5534 10342 4808
00001 5534 10342 4808
00002 4567 7890 3323
00002 4567 7890 3323
00002 4567 7890 3323

[novinosrin · Accepted solution]

data have;
input id $ first_date last_date;
cards;
00001 5534 .
00001 . 10342
00002 4567 .
00002 . .
00002 .  7800
;

data want;
 do _n_=1 by 1 until(last.id);
  update have(obs=0) have;
  by id;
 end;
 do _n_=1 to _n_;
  followup_date=last_date-first_date;
  output;
 end;
run;

proc print noobs;run;

id	first_date	last_date	followup_date
00001	5534	10342	4808
00001	5534	10342	4808
00002	4567	7800	3233
00002	4567	7800	3233
00002	4567	7800	3233

[Bksong]

Thank you so much.