how to count something using proc sql

[appleorange]

I have a dataset (patients) as such:

Pat_ID     Hos     Date

A              11        1/1/2012

B              12         2/3/2012

B              13         2/3/2012

C              11         4/1/2012

C               11         4/5/2012

How do I count using proc sql such that the outcome looks something like this:

Pat_ID      Visits

A                 1

B                   1

C                    2

Since B has two visits on the same date, they are considered as only 1 visit, whereas C has 2 visits because they are on different dates.

[billfish · Accepted solution]

you can try:

proc sql;

select pat_id, count(distinct date) as visits

from   patients

group by pat_id;

quit;