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Re: st: -stylerules- updated on SSC


From   Roger Newson <roger.newson@kcl.ac.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: -stylerules- updated on SSC
Date   Thu, 14 Apr 2005 12:19:20 +0100

Re Point 1, file input and output is usually MUCH more time-consuming than in-memory operations such as checking `touse'. However, re Point 2, Richard is right, and a block of code which modifies the data *permanently* should indeed start with a single -preserve- and end with a single -restore, not-, just in case the user presses -break-.

Roger


At 01:40 14/04/2005, Richard Williams wrote:

At 04:07 PM 4/13/2005 +0100, Nick Cox wrote:
The package -stylerules- on SSC has been
updated. I started by making a few changes
in the light of Stata 9, but mostly thought
of some other things to mention while
I was doing that.
Some very good rules there Nick. I'd be curious what thoughts people have about this one:

"Avoid preserve if possible. preserve is attractive to the programmer but can be expensive in time for the user with large data files. Programmers should learn to master marksample."

Suppose I ignore that advise and instead do something like

preserve
keep if `touse'

1. Will I gain some speed, because Stata will be working with a smaller data set and won't have to repeatedly process -if `touse'- commands?

2. Isn't there a potential tradeoff between this and another rule, respect the dataset? If you don't preserve, there is a greater burden on the programmer to make sure all is well at the end of the run. But, isn't there also a greater risk if, say, the user stops the program before completion?

I suppose good, careful programmers can guarantee both speed and security of data. But, I would add the caveat that, if you are not 100% confident of your programming, you might want to favor safety over speed.


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--
Roger Newson
Lecturer in Medical Statistics
Department of Public Health Sciences
Division of Asthma, Allergy and Lung Biology
King's College London

5th Floor, Capital House
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Email: roger.newson@kcl.ac.uk
Website: http://phs.kcl.ac.uk/rogernewson/

Opinions expressed are those of the author, not the institution.

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