Date:         Thu, 21 Jun 2007 09:33:39 -0400
Reply-To:     "Fehd, Ronald J. (CDC/CCHIS/NCPHI)" <rjf2@CDC.GOV>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         "Fehd, Ronald J. (CDC/CCHIS/NCPHI)" <rjf2@CDC.GOV>
Subject:      Re: Questions to Dorfman's DO UNTIL loop
In-Reply-To:  <JHEEIGIGFPGACEGDPJMGEEEBJMAA.bardos2@ansys.ch>
Content-Type: text/plain; charset=us-ascii

> From: Robert Bardos

> Paul Dorfman's very interesting post and solution to the
> recent 'two-variable deduplication problem' thread had me
> stumped and I have to admit that I have some difficulty
> understanding why his 'do until (0)' technique works the way it does.

I reference Paul Dorman's Most Excellent Paper:
The Magificent Do

http://www.devenezia.com/papers/other-authors/sesug-2002/TheMagnificentD
O.pdf

in my Paper sgf2007.067:
DO Which? Loop, UNTIL, or WHILE?
A Review of DATA Step and Macro Algorithms

http://www2.sas.com/proceedings/forum2007/067-2007.pdf

Ron Fehd  the macro maven  CDC Atlanta GA USA RJF2 at cdc dot gov


> I stripped the data step down to this (while choosing 'do
> until (1=2)' for clarity.)
>
>    data _null_ ;
>      put 'before set iteration' _n_ 2.;
>      do until (1=2);
>        set sashelp.class(obs=3) end=eod;
>      end;
>      put 'after  set iteration' _n_ 2.;
>    run ;
>
> The log shows:
>
>    before set iteration 1
>
> Now contrast this with
>
>    data _null_ ;
>      put 'before set iteration' _n_ 2.;
>      do until (eod);
>        set sashelp.class(obs=3) end=eod;
>      end;
>      put 'after  set iteration' _n_ 2.;
>    run ;
>
> Where the log shows:
>
>    before set iteration 1
>    after  set iteration 1
>    before set iteration 2
>
> The surprising (to me) thing here being the fact that
> executing the first piece of code neither of the last two put
> statements that the second piece of code displayed showed up.
>
> For the first piece of code I had expected the three log
> lines as displayed by the second piece of code *plus* a 'data
> step stopped due to looping' message.
>
> I guess what surprises me most is the 'after' message not showing up.
>
> Anybody care to explain what exactly happens in the first data step?
>
> Many thanks in advance (and many thanks to everybody
> answering my 'dying IT skills URL link missing' question)
>
> Robert Bardos
> Ansys AG, Zurich, Switzerland