SAS - using a formatted (date) variable to aggregate data

sas_format_proc_means_summary.sas

/*Note that if you apply formats to your date they get grouped according to the format, so having a SAS date is advantageous.
Here's a quick example that shows the calculating of yearly statistics from a data set.*/

proc means data=sashelp.stocks N NMISS min max mean median STACKODS;
class date;
format date year4.;
var open high low;
output out=want n= mean= sum= median= mean= / autoname autolabel;
ods output summary = want2;
run;