I need to order survey data by date and month and add rows for missing data

[fordcr2]

I have survey data for participants over a year long study, but not everyone filled out a survey each month as expected. There are a lot of people in this dataset so I want to do this systematically.  Some people have surveys in multiple years ex) their first survey may be in November 2021 but they have surveys through 2022. 

Survey_m_y	q1	q2	q3
June 2021	1	2	0
August 2021	3	4	2
September 2021	4	0	3

I want the data to look like this:

Survey_m_y	study_time	q1	q2	q3
June 2021	1	1	2	0
July 2021	2
August 2021	3	3	4	2
September 2021	4	4	0	3

What is the easiest way to fill in the missing month/year dates so that I can assign a study_time variable for each person that has 12 observations?

[PaigeMiller]

Work with actual numeric SAS dates, instead of text strings like "June 2021". Numeric dates will sort properly and makes it much easier for you to detect gaps.

[fordcr2]

I have the dates and can use those, but how would I fill in the missing months still? 

[PaigeMiller]

Example assuming you have numeric dates representing the 1st day of each month, fake data from Jan 2020 to Jan 2022

data have;
    date=mdy(1,1,2020);
    q1=1;
    output;
    date=mdy(4,1,2020);
    q1=4;
    output;
    format date monyy7.;
run;
data all_months;
    start_date=mdy(1,1,2020);
    do study_time = 0 to 24;
        date=intnx('month',start_date,count,'b');
        output;
    end;
    format date monyy7.;
    drop start_date;
run;
data want;
    merge have all_months;
    by date;
run;