I have a data set with weekly case counts of a disease by municipality by country. I need to aggregate it to monthly case counts to reduce the number of observations for future analysis. I've looked around and can't get the various tips to work for me. Any advise? I currently have 200,000 observations and I need to reduce them, thus the desire to have a data set by monthly counts.   Variables I have country - character, 3 levels municipality - character, ~6000 levels date - numeric, MMDDYY10. cases, numeric habitat, character, 5 levels   PROC SQL; *taking weekly data and aggregating to monthly; create table monthly as select id,country,month,date,habitat,SUM(cases) as Monthly_cases FROM weekly *name of dataset; GROUP BY ID,DATE; QUIT;  Running this code still leaves me with the 200,000 observations... ... View more