How to Count Distinct for SAS PROC SQL with Rolling Date Window of 5 years? - sas

Question

I want to count the distinct values of a variable grouped by MEMBER_ID and a rolling date range of 5 years. I have seen a similar post.
How to Count Distinct for SAS PROC SQL with Rolling Date Window?
When I change h2.DATE BETWEEN h.DATE - 180 AND h.DATE to h2.year BETWEEN h.year-5 AND h.year, should it give me the correct distinct count within the last 5 years? Thank you in advance.
data have;
input permno year Cand_ID$;
datalines;
1 2000 1
1 2001 2
1 2002 3
1 2003 1
1 2004 3
1 2005 1
2 2000 1
2 2001 3
2 2002 1
2 2003 2
2 2004 2
2 2005 2
2 2006 1
2 2007 1
3 2001 3
3 2002 3
3 2003 3
3 2004 1
3 2005 1
;
run;

Answer 1

Here's how you can do it with a data step. This assumes you have values for all years. If you do not, fill it in with zeros.
Keep a rolling list of the last 5 years by using the lag function. If we keep a rolling sorted array list of the last 5 years using lag, we can count the distinct values for each row to get a rolling 5-year count.
In other words, we're going to create and count a list that looks like this:
permno year id1 id2 id3 id4 id5
1 2000 . . . . 1
1 2001 . . . 1 2
1 2002 . . 1 2 3
1 2003 . 1 1 2 3
Code:
data want;
set have;
by permno year;
array lagid[4] $;
array id[5] $;
id1 = cand_id;
lagid1 = lag1(cand_id);
lagid2 = lag2(cand_id);
lagid3 = lag3(cand_id);
lagid4 = lag4(cand_id);
/* Reset the counter for the first group */
if(first.permno) then n = 0;
/* Count the number of rows within a group */
n+1;
/* Save the last 5 years by using the lag function,
but do not get lags from previous groups
*/
do i = 1 to 4;
if(i < n) then id[i+1] = lagid[i];
end;
/* Sort the array of IDs into ascending order */
call sortc(of id:);
/* Count the number of distinct IDs in the array. Do not count
missing values.
*/
n_distinct = 1;
do i = 2 to dim(id);
if(id[i] > id[i-1] AND NOT missing(id[i-1]) ) then n_distinct+1;
end;
drop lag: n i;
run;
Output (without id: dropped):
permno year Cand_ID id1 id2 id3 id4 id5 n_distinct
1 2000 1 . . . . 1 1
1 2001 2 . . . 1 2 2
1 2002 3 . . 1 2 3 3
1 2003 1 . 1 1 2 3 3
1 2004 3 1 1 2 3 3 3
1 2005 1 1 1 2 3 3 3