topic Re: do loop in SAS Programming

do loop

vstorme — Thu, 04 Oct 2018 07:29:41 GMT

Dear SAS users,

I have a basic question. Why is i 5.5 upon the following code when the output statement is not given:

data A;
do i = 1 to 5 by 0.5;
   y = i**2; 
   output;
end;
run;
proc print data = A;
run;

data A;
do i = 1 to 5 by 0.5;
   y = i**2; 
end;
run;
proc print data = A;
run;

Re: do loop

RW9 — Thu, 04 Oct 2018 07:38:12 GMT

Read the manual!

i is incremented at the end of the loop to 5.5, however as that is over the top boundary for the do loop, the do loop then exits. The incremenetor will always (upon complete run) be one iteration count above the upper bound. Its a bit like saying:

set i to lower limit
start
is i over upper limit, no then do
  ...
increment i by one iteration and return to start

Re: do loop

s_lassen — Thu, 04 Oct 2018 07:39:44 GMT

I suppose you mean your last data step. The thing is this: if there is no explicit OUTPUT statement in a data step, SAS puts an implicit output statement at the end of the data step. After the loop has run, I=5.5, and that value is output. But for Y you will get 4.5**2, as that was the last assignment inside the loop.

Re: do loop

Kurt_Bremser — Thu, 04 Oct 2018 08:28:57 GMT

In code,

do i = 1 to 5 by 0.5;
end;

translates to

i = 1;
do while (i <= 5);
  i + 0.5;
end;

Re: do loop

vstorme — Thu, 04 Oct 2018 10:07:11 GMT

I can see that, but when you do add output as in the first case, i=5 in the last observation

Re: do loop

Kurt_Bremser — Thu, 04 Oct 2018 10:30:44 GMT

@vstorme wrote:

I can see that, but when you do add output as in the first case, i=5 in the last observation

That's because the implicit

i + 0.5;

comes after the execution of the output statement, and no implicit output is done after the do loop finishes.

Do this for reference:

data A;
do i = 1 to 5 by 0.5;
   y = i**2; 
   output;
  put i=;
end;
put i=;
run;