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Re: st: Recode slow


From   Ulrich Kohler <kohler@wz-berlin.de>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Recode slow
Date   Tue, 25 Oct 2005 11:30:35 +0200

Brendan Halpin wrote:
> Is it normal that recode should be very slow with large numbers of
> "rules"? I find a recode statement with >400 value assignments adds
> something of the order of a minute to a job.
>
> N is moderately large (75k) but I wonder if recode is linear in N
> but non-linear in the number of rules or assignments.
>
> If so, any tips for efficiency? Break up the command into several
> smaller recodes? Ship out the equivalences to a lookup table and
> merge?

I don't know how it depends on N and the number of rules, but be aware that 
-recode- is merely a wrapper for -generate- and -replace-. Hence -recode- 
interprets what the user says, constructs the -generate- and -replace- 
commands that are equivalent and let Stata process thru these -generate- and 
-replace- statements. Stata it is always faster if you write down the 
equivalent -generate- and -replace- commands -- but you will probably want  
to add the writing-time to the processing-time. 

Personally I never use -recode-. Instead I build -generate/replace statements- 
with  -inlist()- and -inrange()-, which are fast in writing _and_ processing. 
Also note Stata-Tip 16 "Using input to generate variables" (SJ 5,1 134-135) 
and Kantor/Cox "Depening on conditions: a tutorial on the cond() 
function" (SJ 5,3 405-412) 

Shipping out the equivalences to a lookup table and merging is always worth 
thinking about. 

Many regards
uli

-- 
kohler@wz-berlin.de
+49 (030) 25491-361
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