Date:         Fri, 4 Nov 2005 13:32:55 -0500
Reply-To:     Chang Chung <chang_y_chung@HOTMAIL.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Chang Chung <chang_y_chung@HOTMAIL.COM>
Subject:      Re: Trying to avoid division by zero...
Comments: To: Dale McLerran <stringplayer_2@YAHOO.COM>

On Fri, 4 Nov 2005 10:09:50 -0800, Dale McLerran <stringplayer_2@YAHOO.COM>
wrote:

>--- Kevin Myers <KMyers@PROCOMINC.NET> wrote:
>
>> By the way, here is an only slightly uglier macro to get around
>> division by
>> zero messages within expressions, if you really need to:
>>
>> %macro zdiv(n,d);
>> ifn(&d,(&n)/ifn(&d,&d,1),.)
>> %mend zdiv;
>>
>> Usage example:
>>
>> data _null_;
>>    do d=0 to 5;
>>       r=%zdiv(1,d);
>>       put d= r=;
>>    end;
>> run;
>>
>> As provided above, this macro also avoids messages if the denominator
>> is
>> missing.  Of course that could be changed very easily if desired.
>>
>> s/KAM
>
>Kevin posted this inline macro for performing division without
>generating notes that indicate division by zero.  I would observe
>that if the denominator is missing, then Kevin's code also avoids
>notes that inform about performing operations on missing values.
>However, if the numerator is missing, notes are generated about
>performing operations on missing values when Kevin's macro is used.
>
>In the spirit of an inline macro which performs division when
>the numerator is nonmissing and the denominator is both nonmissing
>and nonzero, I offer this further uglification of Kevin's macro.
>(I am compelled here to conjure up images of Dufflepuds from C.S.
>Lewis' "Voyage of the Dawn Treader".  Fans of the Chronicles of
>Narnia will have no problem remembering that the Dufflepuds were
>uglified by the magician.)  Herewith is my further uglification:
>
>
>%macro zdiv(n,d);
>/**************************************************************/
>/* macro ZDIV divides the numerator &n by the denominator &d  */
>/* If the denominator is missing or zero, the division is not */
>/* performed and the result is set to missing.  Also, if the  */
>/* numerator is missing, the division is not performed and    */
>/* the result is set to missing.                              */
>
>/* macro ZDIV is an inline macro.  It does not produce any    */
>/* semicolons indicating end-of-statement.  Thus, it can be   */
>/* employed within a condition, as                            */
>/*                                                            */
>/*   if %zdiv(num,denom)>1 then do;                           */
>/*      <code when true>                                      */
>/*   end;                                                     */
>/**************************************************************/
>ifn(&n>.Z, ifn(&d, ifn(&n,&n,0,0)/ifn(&d,&d,1),.), .)
>%mend zdiv;
>
>
>/*Usage example:*/
>
>data _null_;
>   do num=1, -1, .;
>      do denom=., 0 to 5;
>         r=%zdiv(num,denom);
>         put num= denom= r=;
>      end;
>   end;
>run;
>
>
>I would note that this is NOT efficient code.  If we were to
>write code with an IF condition which examines both numerator
>and denominator for proper values, we would improve efficiency
>considerably.  But if you demand inline code which will operate
>without producing those nasty notes about division by zero or
>operating on missing values, then the macro presented here may
>be employed.
>
>Dale

Hi,
This is such a great one-liner... I am definitely keeping this one. Many
many thanks to Dale and Kevin.
Cheers,
Chang