How to Count Dates within Certain Range

[A_SAS_Man]

I am trying to look at different lines of data and count how many times a line falls within 30 days of previous lines for the same id and code. I have been trying to do this with a data step but haven't been able to figure it out and am open to any solutions.

Here is my starting data.

data have;
input id code date :date9.;
format date date9.;
datalines;
4350 1 '01JUN2021'd
4350 1 '13JUN2021'd
4456 3 '27JUL2021'd
4456 4 '27NOV2021'd
1234 1 '01JAN2021'd
1234 1 '10JAN2021'd
1234 1 '21JAN2021'd
;
run;

Here is what I'm trying to generate.

data want;
input id code date :date9. count;
format date date9.;
datalines;
4350 1 '01JUN2021'd 0
4350 1 '13JUN2021'd 1
4456 3 '27JUL2021'd 0
4456 4 '27NOV2021'd 0
1234 1 '01JAN2021'd 0
1234 1 '10JAN2021'd 1
1234 1 '21JAN2021'd 2
;
run;

[Kurt_Bremser]

In a data step, use BY processing and LAG to compare with the previous value.

data want;
set have;
by id notsorted code;
if not first.code and date - lag(date) le 30
then count + 1;
else count = 0;
run;

The SUM statement (count + 1) implies an automatic RETAIN.

[A_SAS_Man]

This is very close, but it seems to "overcount" in some instances. See below modified example to demonstrate.

data have;
input id code date :date9.;
format date date9.;
datalines;
4350 1 '01JUN2021'd
4350 1 '13JUN2021'd
4456 3 '27JUL2021'd
4456 4 '27NOV2021'd
1234 1 '01JAN2021'd
1234 1 '10JAN2021'd
1234 1 '21JAN2021'd
1234 1 '15FEB2021'd
;
run;

Your code would produce this:

data code_output;
input id code date :date9. count;
format date date9.;
datalines;
4350 1 '01JUN2021'd 0
4350 1 '13JUN2021'd 1
4456 3 '27JUL2021'd 0
4456 4 '27NOV2021'd 0
1234 1 '01JAN2021'd 0
1234 1 '10JAN2021'd 1
1234 1 '21JAN2021'd 2
1234 1 '15FEB2021'd 3
;
run;

What I'm trying to get is this:

data want;
input id code date :date9. count;
format date date9.;
datalines;
4350 1 '01JUN2021'd 0
4350 1 '13JUN2021'd 1
4456 3 '27JUL2021'd 0
4456 4 '27NOV2021'd 0
1234 1 '01JAN2021'd 0
1234 1 '10JAN2021'd 1
1234 1 '21JAN2021'd 2
1234 1 '15FEB2021'd 1
;
run;

This is because the last line is only within 30 days of one of the other lines with matching codes and ids.

[Kurt_Bremser · Accepted solution]

So if I interpret you right, we need to keep a starting date for the group, and start a new group when we go past 30 days of that:

data want;
set have;
by id notsorted code;
retain start_date;
l_date = lag(date);
if first.code then start_date = date;
if not first.code and date - l_date le 30
then do;
  if date - start_date le 30
  then count + 1;
  else do;
    count = 1;
    start_date = l_date;
  end;
end;
else count = 0;
drop l_date start_date;
run;

[ballardw]

You can save yourself a bit of typing for the data lines in your code:

data have;
input id code date :date9.;
format date date9.;
datalines;
4350 1 01JUN2021
4350 1 13JUN2021
4456 3 27JUL2021
4456 4 27NOV2021
1234 1 01JAN2021
1234 1 10JAN2021
1234 1 21JAN2021
;
run;

the quotes and d are needed to define a literal date in code and not needed, and potentially can cause errors when reading the data.