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RE: st: nesting functions in R


From   "Feiveson, Alan H. (JSC-SK311)" <alan.h.feiveson@nasa.gov>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: nesting functions in R
Date   Tue, 10 Jul 2007 10:30:46 -0500

whether Stata should allow syntax such as

 reg y log(x1) x2/x3 

AL Feiveson

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of David Airey
Sent: Tuesday, July 10, 2007 9:42 AM
To: statalist@hsphsun2.harvard.edu
Subject: re: st: R and Stata efficiency

.

I wrote in a summary of some instances where an R user felt they had
things better in terms efficiency at the command line. Not spending as
much time at Stata _and_ R that would give me a better feeling for
whether comments made were born out of familiarity with both command
lines (and fair judgement) or just one (and relative ignorance of best
practices), I posted.

Phil Schumm kindly replied with some excellent comments. Especially
appreciated was the prefix, -estimates for-, because my R user friend

> One final comment RE use of stored results. In R, once you have fit 
> several models and stored their results you can do something like
> this:
>
> plot(results)
> plot(other_results)
>
> Now, suppose you've done the same in Stata. What I often see users do 
> is the following:
>
> est restore results
> rvplot
> est restore other_results
> rvplot
>
> However, this is unnecessary. Instead, you can simply do
>
> est for results: rvplot
> est for other_results: rvfplot
>
> Notice that the -estimates for- prefix goes a long way toward reducing

> the difference between Stata and R in the ease with which you can use 
> stored results.

I definitely have been overtyping as Phil described, and look forward to
using the -estimates for- prefix (see help estimates in Stata).  
Admittedly, this prefix has stared me in the face as many times as I've
looked up help for estimates, but it is easy to miss how best to use
options best.

One other comments from the R user regarding efficiency was about
nesting functions:

>
> One other issue is that the result of a command (sic in Stata)  
> cannot be used directly as the argument of another commmand.  In R,  
> I can do something like
>
> dhdbeta = A %*% diag(exp(aacoef))
>
> in which, exp() gives the exponential values of the elements in  
> aacoef, then diag() makes a matrix with the diagonal being those  
> exponential values, then the matrix is multiplied on the left by  
> another matrix A. The exp() and diag() are calculated on the fly  
> and discarded afterwards. Their values are not used elsewhere and  
> thus there is no need to save them explicitly just for the next  
> step.  While in Stata, I have save them.
>

--
David C. Airey, Ph.D.
Research Assistant Professor

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