Adding an index variable for interaction diary data - sas

Question

I am working on an interaction diary data set. I got this data file sent to me cleaned, but the people that cleaned it did not add an index variable that I need for analyses. So:
Participants completed survey questionnaires for every interaction that they had over X number of days. This means that participants may have multiple records (interaction diaries) for each day. To do the analyses, I need 3 index variables - Person_id, DiaryDay, and InterOnDay. Like this:
Person_ID
DiaryDay
InterOnDay
2300
1
1
2300
1
2
2300
2
1
2300
2
2
2300
2
3
2300
3
1
I have the first two index variables, but am missing InterOnDay.
Of note, the number of diarydays vary by person, and the number of interactions recorded vary by person and diaryday.
I think I need to do DO loops, but I have just utterly failed at figuring out how. Does anyone have suggestions for how this code might look?
This is what I have so far, but I know this is not enough code.
DATA WORK.TEST;
SET WORK.DT;
by ID DATETODAY;
do IntOnDay = 1 to ;
output;
end;
run;

Answer 1

I think this is what you want.
data have;
input Person_ID DiaryDay;
datalines;
2300 1
2300 1
2300 2
2300 2
2300 2
2300 3
;
data want;
set have;
by Person_ID DiaryDay;
if first.DiaryDay then InterOnDay = 0;
InterOnDay + 1;
run;