Sum over all rows and add as a variable (data step) - sas

Question

I have the following table
Row1, 3
Row2, 5
Row3, 8
and I now want to sum over all rows and place the result as a new variable on all rows, i.e.
Row1, 3, SUM(Row1,Row2,Row3)
Row2, 5, SUM(Row1,Row2,Row3)
Row3, 8, SUM(Row1,Row2,Row3)
Just like sum in proc sql would work... I've tried the simple sum, but that only sums the row. Any tips?

Answer 1

First: the SQL solution, or the PROC solution (where you run PROC MEANS to get the sum and then just incorporate it), is generally substantially preferred to the data step solution in most cases. Using built-in tools is typically better than writing your own tool to replicate something already extant.
However, the data step solution isn't terribly complicated. You just need to use what's known colloquially as a DoW loop (after two of the people who popularized it) and iterate over the dataset twice, once to get the sums and then the second time to output the rows. You can adapt this easily to summing over by-groups by changing until(eof) to until(last.byvar) (byvar being whatever by variable you are summing over) and adding a by group with that byvar inside both of the loops.
data want;
do _n_ = 1 by 1 until (eof);
set sashelp.class end=eof;
sumvar = sum(sumvar,age);
end;
do _n_ = 1 by 1 until (eof1);
set sashelp.class end=eof1;
output;
end;
run;

Answer 2

A SQL sum will accomplish this and merge it back in to the dataset automatically.
You will see a note in the LOG regarding merging the data.
PROC SQL;
Create table want as
Select *, sum(variable2sum) as total
From have;
Quit;
EDIT:
Since SQL wasn't an option, a more common answer is to create the sum in proc means and merge it in. Here's the code for that solution as well:
proc means data=sashelp.class noprint;
output out=summary mean(age)=avg_age;
run;
data class;
set sashelp.class;
if _n_=1 then
set summary;
drop _type_ _freq_;
run;
proc print data=class;
run;