SAS_Specific Conditional Sum_ - sas

Question

I have a question on SAS Programming. It is about conditional sum. But it is very specific for me. Therefore, I want to ask as an example. I have the following dataset:
Group A Quantity
1 10 7
1 8 4
1 7 3
1 10 5
2 11 6
2 13 8
2 9 7
2 13 9
I want to add two more columns to this dataset. The new dataset should be:
Group A Quantity B NewColumn
1 10 7 10 12 (7+5)
1 8 4 10 12
1 7 3 10 12
1 10 5 10 12
2 13 6 13 15 (6+9)
2 10 8 13 15
2 9 7 13 15
2 13 9 13 15
So, the column B should be equal tha maximum value of each group and it is the same for all observations of each group. In this example, Group number 1 has 4 values. They are 10, 8, 7, 10. The maximum among these values is 10. Therefore, the values of the observations of the B column for the first group are all equal to 10. Maximum number for group number 2 is 13. Therefore, the values of the observations of the B column for the second group are all equal to 13.
The column C is more complicated. Its value depends on the all columns. Similiar to B column, it will be the same within group. More detailed, it is the sum of the specific observations of QUANTITIES column. These specific observations should belong to the observations that have the maximum value in each group. In our example, it is 12 for the first group. The reason is, the maximum number of first group is 10. and the quantities belong to 10 are 7 and 5. So, the sum of these is 12. For the second group it is 15. because the maximum value of the second group is 13 and the quantities belong to 13 are 6 and 9. So the sum is 15.
I hope. I can explain it. Many thanks in advance.

Answer 1

You can do this with proc sql:
proc sql;
select t.*, max_a as b,
(select sum(t2.quantity)
from t t2
where t2.group = t.group and t.a = max_a
) as c
from t join
(select group, max(a) as max_a
from t
group by group
) g
on t.group = g.group;
run;
If the data is coming from an underlying database, most databases support window functions which make this easier.

Answer 2

This is untested (I'm away from sas) and will probably have mistakes, but a triple DoW loop should work. One pass to get the max per group, second pass to get the sum, third pass to output the records. Something like:
data want ;
do until(last.group) ;
by group ;
set have ;
B=max(A,B) ;
end ;
do until(last.group) ;
set have ;
by group ;
if A = B then NewColumn = sum(NewColumn, Quantity) ;
end;
do until(last.group);
set have ;
by group;
output ;
end ;
run;