topic Re: Combining explicit and implicit loop in SAS Programming

Combining explicit and implicit loop

SAS_inquisitive — Wed, 04 Oct 2017 17:49:14 GMT

Hello,

How does this program execute?


data test;
	set sashelp.class;

	do until(eof);
		set sashelp.class end=eof;
	 output;
	end;
run;

Re: Combining explicit and implicit loop

Kurt_Bremser — Wed, 04 Oct 2017 17:55:20 GMT

Try it, and read the log. If puzzled, come back here.

Re: Combining explicit and implicit loop

mkeintz — Wed, 04 Oct 2017 17:55:43 GMT

Form a hypothesis test it, report the results, and why you think those results occurred. Then you'll get plenty of responses.

Re: Combining explicit and implicit loop

ballardw — Wed, 04 Oct 2017 17:57:43 GMT

Look at the log after running this and see if you get any enlightenment:

data test;
	set sashelp.class;
   put 'Before loop';
	do until(eof);
      put 'At begin of loop' +1 name=;
		set sashelp.class end=eof;
      put 'In loop after set' +1 name=;
	 output;
      put;
	end;
run;

Re: Combining explicit and implicit loop

PGStats — Wed, 04 Oct 2017 18:22:05 GMT

The question you may want to ask instead is When does this program stop?

Re: Combining explicit and implicit loop

SAS_inquisitive — Wed, 04 Oct 2017 18:39:01 GMT

@KurtBremser and @mkeintz I was wondering why two records are reading from first set statement?

Re: Combining explicit and implicit loop

mkeintz — Wed, 04 Oct 2017 18:47:26 GMT

How many times do you think the complete loop "do until (eof); ....... " is successfully run?
What happens when a SET statement attempts to read beyond end of data?

Re: Combining explicit and implicit loop

Rick_SAS — Wed, 04 Oct 2017 19:26:07 GMT

Building on ballardw's advice, try

data test;
	set sashelp.class(rename=(Name=FirstName));
   put 'Before loop';
	do until(eof);
      put 'At begin of loop' +1 FirstName=;
		set sashelp.class end=eof;
      put 'In loop after set' +1 FirstName= +1 name=;
	 output;
      put;
	end;
run;

Re: Combining explicit and implicit loop

SAS_inquisitive — Wed, 04 Oct 2017 20:32:21 GMT

@mkeintz 1. "do until (eof); ....... " runs just in one loop as it is DOW-LOOP setting.

2. _n_ increments by 1 and implicit loop terminates.


data test;
    put _all_;
	set sashelp.class;
	put _all_;
run;

data test;
	
	put _all_;
	do until(eof);
      
		set sashelp.class end=eof;
		output;
    put _all_;
	end;
	
run;

Re: Combining explicit and implicit loop

SAS_inquisitive — Wed, 04 Oct 2017 21:00:56 GMT

@Rick_SAS, renaming helped understand since the original solution was given by @Ballard, I accepted his solution. Thanks .

Re: Combining explicit and implicit loop

Kurt_Bremser — Thu, 05 Oct 2017 06:48:47 GMT

A nice variation to further illustrate the behaviour of set statements and loops:

data test;
  set sashelp.class;
  do while (not eof);
    set sashelp.class end=eof;
    output;
  end;
run;

Re: Combining explicit and implicit loop

SAS_inquisitive — Sat, 07 Oct 2017 22:22:52 GMT

@PGStats, you are absolutely right.