RE: st: re: averaging within a variable

["kelly johnson" <econometrics@hotmail.com>]

now suppose I had to do this operation in 100 different variabes (call them 
var1-var100), how can i code a simple loot to do that?

i want to perform this within each variable: gen  Var2=(Var1+Var1[_n-1])/2 
if mod(_n,2)==0

(even _n calculations are fine...)

Thanks!



> From: Kit Baum <baum@bc.edu>
> Reply-To: statalist@hsphsun2.harvard.edu
> To: statalist@hsphsun2.harvard.edu
> Subject: st: re: averaging within a variable
> Date: Tue, 12 Jul 2005 22:32:13 -0400
>
> Austin said
>
> g  Var2=(Var1+Var1[_n-1])/2 if mod(_n,2)==0
>
> -----Original Message-----
> From: kelly johnson [mailto:econometrics@hotmail.com]
> Sent: Tuesday, July 12, 2005 9:51 PM
> Hi,
> Quick question: suppose I have a variable like this:
> N  Var1
> 1  12
> 2  45
> 3  65
> 100  15
> How can I create a new variable whose first observation is the average of
> Var1[1] and Var1[2], second observation is the avaerage of Var1[3] and
> Var1[4], etc. There will be a total of 50 observations for this new
> variable. Thanks in advance!
>
> Not quite. That creates the even-numbered obs. of Var2 as the desired 
> values, with the odd-numbered values equal to missing. To fix that up, 
> thanks to Bill Gould's excellent tutorial at this morning's Boston SUG 
> meeting, you may use a cute mata trick (in Stata 9, anyway):
>
> clear
> set obs 100
> g Var1=_n
> g  Var2=(Var1+Var1[_n-1])/2 if mod(_n,2)==0
> mata:
> 	v = st_data(.,"Var2",0)  // grab nonmissing elements of Var2
> 	null=J(50,1,.)
> 	v = v\null               // append 50 missings
> 	st_store(.,2,v)          // stuff it back in Var2
> 	end
> list
>
>
> Kit Baum, Boston College Economics
> http://ideas.repec.org/e/pba1.html
>
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