Averages in SAS with dates using months - sas

Question

Let's say I have 50 years of data for each day and month. I also have a column which lists the max rainfall for each day of that dataset. I want to be able to compute the average monthly rainfall and standard deviation for each of those 50 years. How would I accomplish this task? I've considered using PROC MEANS:
PROC MEANS DATA = WORK.rainfall;
BY DATE;
VAR AVG(max_rainfall);
RUN;
but I'm unfamiliar on how to let SAS understand that I want to be using the MM of the MMDDYY format to indicate where to start and stop calculating those averages for each month. I also do not know how I can tell SAS within this PROC MEANS statement on how to format the data correctly, using MMDDYY10. This is why my code fails.
Update: I've also tried using this statement,
proc sql;
create table new as
select date,count(max_rainfall) as rainfall
from WORK.rainfall
group by date;
create table average as
select year(date) as year,month(date) as month,avg(rainfall) as avg
from new
group by year,month;
quit;
but that doesnt solve the problem either, unfortunately. It gives me the wrong values, although it does create a table. Where in my code could I have gone wrong? Am I telling SAS correctly that add all the rainfall's in 30 days and then divide it by the number of days for each month? Here's a snippet of my table.

Answer 1

You can use a format to group the dates for you. But you should use a CLASS statement instead of a BY statement. Here is an example using the dataset SASHELP.STOCKS.
proc means data=sashelp.stocks nway;
where date between '01JAN2005'd and '31DEC2005'd ;
class date ;
format date yymon. ;
var close ;
run;