topic why 'if 0 then set' still copy an empty record? in SAS Programming

why 'if 0 then set' still copy an empty record?

Haikuo — Sat, 07 Apr 2012 03:34:50 GMT

Dear Data step user

data b;

if 0 then set sashelp.class;

run;

proc print ;run;

since it is never actually executed, why there is still an empty record been created?

Thanks,

Haikuo

Re: why 'if 0 then set' still copy an empty record?

art297 — Sat, 07 Apr 2012 04:17:26 GMT

A nice explanation of what occurs when can be found in the following paper: http://www.lexjansen.com/nesug/nesug88/sas_supervisor.pdf

The pdv is populated first, thus the five variables exist. One loop was completed, thus one record has to be output. If you want to do something similar, but not have any loop occur, you could run:

data b;

if 0;

set sashelp.class;

run;

That way, you will still get 5 variables, but 0 records.

Re: why 'if 0 then set' still copy an empty record?

Haikuo — Sat, 07 Apr 2012 12:04:11 GMT

Thanks, Art. That was indeed great paper, I have come across it long before I know anything about pdv, and of course I failed to register. Now everything makes sense, Yeah!

BTW, It has also been known to me that if just wanting the structure, (obs=0) will do, too.

Haikuo

Re: why 'if 0 then set' still copy an empty record?

Tom — Sat, 07 Apr 2012 14:01:59 GMT

You end up with one record because the data step has looped once and output one record.

See how many records you get with the trivial step. data a; run;

To get 0 records you will need to do something to stop it from outputting the record.

Here are some ways:

data b; set sashelp.class(obs=0); run;

data b; if 0 then set sashelp.class; stop; run;

data b; set sashelp.class; if 0 then output; run;

Re: why 'if 0 then set' still copy an empty record?

Haikuo — Sat, 07 Apr 2012 19:47:18 GMT

Thanks, Tom. Your examples are very helpful! I especially like the third one: if 0 then output. really wicked me out.

Haikuo