Cumulative sum of columns in SAS - sas

Question

I am trying to sum across variables
N1 N2 N3
1 1 1
1 . 1
1 1 .
Want
N1 N2 N3 B1 B2 B3
1 1 1 1 2 3
1 . 1 1 1 2
1 1 . 1 2 2
The array that I am trying looks like not working at all..
data temp2;
set temp;
array hh(*) N:;
array bb(3);
do i=1 to dim(hh);
bb(i)=bb(i)+hh(i+1);
end;
run;
I dont want to use transpose and cumulate the sum.

Answer 1

First, you have an error in your algorithm: a cumulated value
should not be calculated from itself an the next input value,
but from the previous cumulated value and the corresponding input value.
You rather need bb(i) = bb(i-1) + hh(i). Of course, this does not work when i is 1 because there is no hh(0), so you start doing this from i = 2 on.
Second, you need to handle missing values, something like a coalesce in SQL. Let us use ifn for that, a function that returns a numeric variable. The first argument is a condition, the second is the return value if the condition is true, the third the value the returnvale if the condition is false.
Putting it all together;
data AFTER;
set TEMP;
array hh(*) N:;
array bb(3);
bb1 = ifn(missing(N1), 0, N1);
do i=2 to 3;
bb(i) = bb(i-1) + ifn(missing(hh(i)), 0, hh(i));
end;
drop i;
run;
The down side of this sollution is the hardcoded 3 in array bb(3) and do i=2 to 3, which user3658367 tryed to solve with dim(hh). Unfortunately, that only works for one of them.
So this is better;
proc sql;
select count(*)
into :B_count
from sasHelp.vColumn
where libname eq 'WORK'
and memName eq 'TEMP'
and name like 'N%';
quit;
data AFTER;
set TEMP;
array hh(*) N:;
array bb(&B_count);
bb1 = ifn(missing(N1), 0, N1);
do i=2 to &B_count;
bb(i) = bb(i-1) + ifn(missing(hh(i)), 0, hh(i));
end;
drop i;
run;
I added the condition name like 'N%' because I assume in your real live problem TEMP has other variable than the once you are cummulating.
About the comments below : if you were not involved in this post from the start, you can neglect them. I included them in the text above.
(To the autors of these comments: thanks for your input.)

Answer 2

I am not very comfortable with arrays, so I would use a macro to do the work.
data temp;
input N1 N2 N3;
datalines;
1 1 1
1 . 1
1 1 .
;
run;
options mprint mlogic;
proc sql;
select name into:cols separated by ','
from dictionary.columns
where libname = upcase("work") and memname = upcase("temp") and upcase(name) like 'N%';
quit;
%macro cumul_colsum;
data temp2;
set temp;
run;
%do i = 1 %to %sysfunc(countw(%superq(cols)));
%let var = %scan(%superq(cols),&i,%str(,)); %put |&var|;
data temp2;
set temp2;
B&i. = sum(of N1-&var.);
run;
%end;
%mend cumul_colsum; %cumul_colsum;
And get the desired result, which in this case is the one OP requires. I have used the like 'N%' same as Dirk to feed the column names to a macro, and a do loop to create the columns with cumulative sums. This might take a while for huge datasets. But it's just easier to understand (options mprint nonotes;) what's happening.

Answer 3

follow #Reeza suggestion of using sum instead of + for handing missing values. something like below.
data have;
input
N1 N2 N3;
datalines;
1 1 1
1 . 1
1 1 .
;
data temp2;
set have;
array hh(*) N1 N2 N3;
array bb(3) b1 b2 B3;
do i= 1 to dim(hh);
if i= 1 then bb(i) = hh(i);
else bb(i)= sum(bb(i-1),hh(i));
end;
drop i;
run;