How to Number Visit Dates per ID.

[daszlosek]

Hello all,

I am trying to create a visit date for for each date that a subject has. The first date would be "visit 1", second "visit 2", etc. In the past I have sorted by id and date, then picked first.id or last.id, but in this case I have more than two dates per an id. 

Example start data:

ID	Date
1	10-Mar-15
1	12-Mar-15
1	16-Apr-15
2	1-Apr-15
2	8-Apr-15
3	2-Feb-15
3	8-Feb-16
3	11-Feb-16

And I would like it to end up as:

ID	Date	Visit
1	10-Mar-15	1
1	12-Mar-15	2
1	16-Apr-15	3
2	1-Apr-15	1
2	8-Apr-15	2
3	2-Feb-15	1
3	8-Feb-16	2
3	11-Feb-16	3

I have looked on the forum and stack overflow with no luck so far. I assumed this would be a common question so parhaps I am just looking in the wrong places. Regardless, thank you in advance for the help.

[mkeintz · Accepted solution]

If the data is already sorted by id/date, then:

data want;

  set have;

  by id;

  visit+1;

  if first.id then visit=1;

run;

[daszlosek]

Worked like a charm. Had some difficulty initially due to defining the visit variable in the previous datastep for some reason. Thanks a bunch!