Help using Base SAS procedures

Sum column based on row count

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Occasional Learner
Posts: 1

Sum column based on row count

Hello,

 

I have searched all over and can't seem to find an answer for this. For each row, I am attempting to sum the values of the next x rows (3 in the example below) for each item.

 

Example: Item 1, row count for aggregation = 3, next 3 rows countain 10 in each row which equals a sum of 30.  It only sums for the item that corresponds to the row that the sum calculation is on (similar to a group by). 

 

The example below is far simpler than my real data which contains different values for sales for each row.


I am assuming that this would be an iterating do until loop of some sort but I can't seem to think of a strategy.  Thanks for all of your insight!

 

ItemSalesSumRolling
11030
11030
11030
11030
11030
11030
11020
11010
22060
22060
22060
22060
22060
22040
22020
Super User
Posts: 18,603

Re: Sum column based on row count

Do you have SAS ETS? If so, a CONVERT statement is your best bet.

 

If not, the quickest way, IMO is to reverse the data, use the LAG function and then reverse the data order again. Assuming you can do the re-ordering yourself, here's how the data step may look. 

 

data want; 
by item sales;

l1=lag(sales);
l2=lag2(sales);
l3=lag3(sales);

if first.item then count=1; else count+1;

if count > 3 then do;
sum = sum(l1, l2, l3);
end;

run;
Super User
Posts: 9,782

Re: Sum column based on row count


data have;
infile cards expandtabs;
input Item	Sales;
cards;
1	10	30
1	10	30
1	10	30
1	10	30
1	10	30
1	10	30
1	10	20
1	10	10
2	20	60
2	20	60
2	20	60
2	20	60
2	20	60
2	20	40
2	20
;
run;
data have;
 set have;
 by item;
 if first.item then n=0;
 n+1;
run;
proc sql;
select a.*,(select sum(sales) from have where item=a.item and 
n between a.n and a.n+2) as rolling_sum
 from have as a;
quit;
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