Simplest way to create a variable equal to a column's grand total in a data step

[everyone]

I'm wondering what's the best way to create a variable that contains a column's total sum inside of a data step. Can this be easily achieved without proc sql?

As an example, I'd like to create a new variable, total_age, that contains the sum of all the students' ages, in the sashelp.class dataset. My code below creates a cumulative sum, but how would I revise to create a total so that each row displays the total age? Thank you.  

data sas_intro;
set sashelp.class;
retain;
total_age = sum(total_age, age); /*creates cumulative sum, not total)*/
run;

[Reeza]

It's either two steps in a data step (calculation + merge) or a DoW loop. Programmatically, SQL is much easier here for sure.

Depending on what you're doing, for example creating a report, the reporting procedure may be better suited to doing that as well.

data sas_intro;
do _n_ =1 by 1 until(eof);
set sashelp.class end=eof;
total_age = sum(total_age, age); /*creates cumulative sum, not total)*/
end;

do _n_ =1 by 1 until(eof2);
set sashelp.class end=eof2;
output;
end;


run;

Other methods illustrated here:

https://github.com/statgeek/SAS-Tutorials/blob/master/add_average_value_to_dataset.sas

[PeterClemmensen]

An SQL approach

proc sql;
   create table want as
   select *
        , sum(age) as total_age 
   from sashelp.class
   ;
quit;

[PeterClemmensen · Accepted solution]

A data step approach

data want;
   if _N_ = 1 then do;
      do until (z);
         set sashelp.class end = z;
         total_age = sum(total_age, age);
         retain total_age;
      end;
   end;

   set sashelp.class;
   
run;