SAS Summing a dynamic range in array - arrays

Question

I have an array with totals for 210 days. I need to find the sum of all 90 day ranges. The new array is med_sum. So med_sum(1) =sum(of Total(32)-total(121)), then med_sum(2)=sum(of total(33)-total(122)), and so on, 90 different times all the way to med_sum(90)=sum(of total(121)-total(210)).
Below is the syntax, but the sum(of) function isn't allowing me to do this and errors out. I have tried quite a few different options but have been unable to find anything that works.
Thank you in advance!!
data work.total_base_3;
set work.total_base_2;
array med_total(*) total1-total210;
array med_sum(*) avg1-avg90;
do i = 1 to 90;
med_sum(i)=sum(of med_total(i+31)-med_total(i+120));
end;
run;

Answer 1

You cannot use array references in variable lists, just actual variable names. So you want to generate 90 sums of 90 values with the window sliding. In essence you want
avg1 = sum(of total32 - total121);
avg2 = sum(of total33 - total122);
avg3 = sum(of total34 - total123);
You could use macro logic to just generate that series of statements. But if you look at the relationship between the variables you can see that
med_sum(n+1) = sum(med_sum(n),med_total(n+1+120),-1*med_total(n+31));
So your loop will look something like:
med_sum(1) = sum(of total32-total121);
do n=1 to dim(med_sum)-1;
med_sum(n+1) = sum(med_sum(n),med_total(n+1+120),-1*med_total(n+31));
end;

Answer 2

here's a sample that you should be able to extend to your data (so in your case you would change the 3's to 90's):
case 1 Data in rows :
data test;
keep obs;
do i=1 to 10;
obs = i;
output;
end;
run;
data test1;
set test;
keep obs sum;
array x[3];
retain x;
x[mod(_n_ -1,3)+1] = obs;
if (_n_ >= 3)then do;
sum = 0;
do i = 1 to 3;
sum= sum + x[i];
end;
end;
run;
case 2 data in columns (use the test dataset from from above):
proc transpose data=test out=testrow;
var obs;
run;
data test2;
set testrow;
array med_total(*) col1-col10;
array med_sum(8) ;
do i = 3 to 10;
med_sum[i-2]=0;
do j = 1 +(i-3) to i;
med_sum(i-2)=med_sum[i-2] + med_total(j);
end;
end;
run;