topic i+1 statement in Do Loops in SAS Software for Learning Community

i+1 statement in Do Loops

Naive_help — Sat, 10 Sep 2022 00:27:36 GMT

I have two programs -

DATA A1;
DO I=1 TO 10;
X+1;
OUTPUT;
END;
RUN;

Created the data set as

DATA A2;
DO I=1 TO 10;
i+1;
X+1;
OUTPUT;
END;
RUN;

created the data set as

I would appreciate it if you could explain how i+1 statement works on the second program.

Thanks!

Re: i+1 statement in Do Loops

Kurt_Bremser — Sat, 10 Sep 2022 01:04:29 GMT

An iterative DO loop looks like this after the compiler does its work:

/* do i = 1 to 10 */

i = 1;
start:
if i > 10 then goto end;
/* "body" of the loop */
i = i + 1;
goto start;
end:

Now, if you code an additional increment of the loop variable into the loop, both increments will be executed.

Re: i+1 statement in Do Loops

kumar75 — Sat, 10 Sep 2022 13:00:26 GMT

@Kurt_Bremser Thank you for the feedback. The explanation on i+1 is not clear to me. I would appreciate it if you could explain how it works on PDV.

Re: i+1 statement in Do Loops

Kurt_Bremser — Sat, 10 Sep 2022 14:13:44 GMT

At the startof the DO loop, i is set to 1.

Then you increment it with the i+1 sum statement, so it becomes 2, which is the value written to the output.

Then the DO loop does its own increment, setting i to 3, after which (in the next DO iteration) you again increment, so 4 is written to the output.

Repeat until i is set to 11 by the internal increment of the DO loop, which then terminates.

Re: i+1 statement in Do Loops

Tom — Sat, 10 Sep 2022 14:25:46 GMT

The sum statement:

i+1;

Performs this assignment statement.

i=sum(i,1);

In addition it flags the variable I to be retained (not reset to missing on the next iteration of the data step). And if there is no other RETAIN statement that is setting a a different initial value the variable is initialized to zero.

Since this data step only iterates once whether or not the variable is retained makes no different. Since the DO loop will overwrite any initial value of I you can replace the sum statement with a simple assignment statement instead.

Re: i+1 statement in Do Loops

kumar75 — Mon, 12 Sep 2022 01:07:10 GMT

Thank you!