Date:         Tue, 23 Apr 1996 13:53:06 +0100
Reply-To:     John Whittington <johnw@MAG-NET.CO.UK>
Sender:       "SAS(r) Discussion" <SAS-L@UGA.CC.UGA.EDU>
From:         John Whittington <johnw@MAG-NET.CO.UK>
Subject:      Re: Geometric Row Mean
Comments: cc: Feldesmanm@pdx.edu

Yesterday I posted the following code for geometric mean:
 
>   array x(*) x1 - x40 ;
>   prod = 1 ;
>   do i = 1 to 40 ;
>      prod = prod * x(i) ;
>   end ;
>   gmean = prod / 40 ;
 
The final line of the code segment obviously should have read:
 
   gmean = prod**(1/40) ;
 
Sorry if I confused anyone.  Following exchanges with the original
questionner, I would add a few other comments/varaints to this:
 
1...If the variables of interest do not have numeric suffices but are known
to be in consecutive positions in the PDV (with first and last known), one
can code:
 
   array x(*) apple -- tomato ;
 
[ if needs be, the ordering of variables in PDV can be forced by a RETAIN
statement at the top of the DATA step]
 
2...If one is wanting to calculate the geometric mean of all numeric
variables in the dataset, then one can code:
 
   array x(*) _numeric_ ;
 
3...If either (1) or (2) above is used, the array declaration must come
*after* the variables are all initialised (e.f. by a SET).
 
4...If missing data may be present and one wants to calculate the geometric
mean of all non-missing values within the list of variables, then one can
extend the code as follows, generalised for any number of variables:
 
   array x(*) x1 - x40 ;  /* or other variable list specifications */
   prod = 1 ;
   do i = 1 to dim(x) ;
      if x(i) ne . then prod = prod * x(i) ;
   end ;
   gmean = prod ** ( 1 / n(of x(*))) ;
 
John
 
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