selecting data in the first 30 days since first date

[fengyuwuzu]

I have 3 variables, ID, order_date, and order_amount for a year, and I want to get the first 30days data starting from the first order date for each ID.

proc sort data=year_data;
by ID order_date;
run;

data first_month;
set year_data;
by ID order_date; 
where day(order_date) - day(first.order_date) <=30; 
run;

this does not work. There is a syntax error at day(first.order_date). What is wrong there?

[LinusH · Accepted solution]

You cannot use first. or last. variables within a where statement since where does the filtering in the input buffers. And that's prior to when the data hits the PDV (and that's where the first. variables are created).

If you wish to accomplish this in a single step look into SQL:
having order_date < min (order_date) +30

[fengyuwuzu]

that works! thank you for teaching me!

[RW9]

Well, you could do something like:

data first_month;
  set year_data;
  by id;
  retain first_date;
  if first.if then first_date=order_date;
  if first_date <= order_date <= intnx('month',first_date,1,'same') then output;
run;

Note I am assuming that date is a date variable not a datetime.  This will output only rows between first_date and first_date+1 month.t

[fengyuwuzu]

Thank you, RW9. This requires both ID and order_date need to be sorted, right? But there is only id in the by statement.

[RW9]

Yes, it reuiqres the data to be sorted, as per the proc sort in your first post.  The date does not need to be in the by line however, what I am doing is retaining the first observation for each id across the id, then using that to compare to the current observations date.

[fengyuwuzu]

Thank you, RW9.