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=========================================================================
Date:         Fri, 21 Feb 2003 10:37:33 -0500
Reply-To:     Howard Schreier <Howard_Schreier@ITA.DOC.GOV>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Howard Schreier <Howard_Schreier@ITA.DOC.GOV>
Subject:      Re: Using a macro to simulate data
Comments: To: WHITLOI1@WESTAT.com
Content-Type: text/plain; charset=US-ASCII

Thanks

I understood about macro and quotation marks in general, but I had the
impression that %sysfunc negated that. So you cannot just copy and paste
an expression from DATA step code into %sysfunc, and you have to "think
macro", at least partly, when coding a %sysfunc argument.

I found a reference to RAND in the "What's New" part of online doc
(http://support.sas.com/documentation/onlinedoc/v81/whatsnew/z1499470.htm),
so I assumed that details would be provided as well. I should assume
less.

>>> Ian Whitlock <WHITLOI1@WESTAT.com> 02/21/03 10:03AM >>>
Howard,

RAND can be found in the HELP facility of 8.2, but the documentation is
very
very sparse.  Remember the function is experimental in 8.2.  That means
you
have to experiment to find out how it works and if you want to use it.
Perhaps the documentation for version 9 is better.

There are no quotes around BETA in the call

  %let theta=%sysfunc(rand(beta,2,3));

because in macro quote marks are literal, i.e. part of the string, as
well
as have meaning (hide some symbolic meaning).  That means when you use
"BETA" the value sent to RAND would be a 6 byte string when RAND was
only
expecting a 4 byte string.

Your suggestion to avoid the proliferation of work data sets is usually
very
good and particularly wise in this case.

IanWhitlock@westat.com

-----Original Message-----
From: Howard_Schreier@ITA.DOC.GOV [mailto:Howard_Schreier@ITA.DOC.GOV]

Sent: Friday, February 21, 2003 7:58 AM
To: SAS-L@LISTSERV.UGA.EDU
Subject: Re: Using a macro to simulate data


Ian has identified the essential problem.

A few additional thoughts ...

Putting the global parameters in a one-observation dataset works, but
a
generally more convenient technique is to use macrovariables:

  %let theta=%sysfunc(rand(beta,2,3));
  %let tau=%sysfunc(sqrt(2.25*(1-&theta**2)));

Maybe Ian will explain why the quotation marks come off the first RAND
parameter.

And, by the way, can anybody help me locate the RAND function in the
online
doc?

Back to Victor's problem: We don't know all of the requirements, but
I'm
wondering if it's necessary to generate separate datasets for the 10
subjects. I generally prefer to stack data together and add a
categorical
variable to use in BY-group processing.

In that case, there is no need for a macro; a single DATA step does
it:

   data tmp(keep=id mu x);
   do id = 1 to 10;
      mu=0.97+15.87*rand('beta',3,3); **ID-specific mean for PM;
      x=0;
      do i=1 to 24;
         x= mu*(1-&theta) + &theta*x + ( &tau*normal(0) );
         if i>20 then output;
         end;
      end;
   run;