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Re: st: Recode slow

From   Brendan Halpin <>
Subject   Re: st: Recode slow
Date   28 Oct 2005 14:14:25 +0100

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?

Just to follow myself up: I succumbed to that temptation described
by Douglas Adams as spending half a day coding something to save
thirty seconds, and switched the big recode to a lookup table.

In running time, the merge lookup (along with necessary sorts etc)
takes under 4 seconds (c 150k cases, >400 categories reassigned).
The recode version takes over 3 minutes to do the same. 

So in fact I spent about half an hour to save about 2m55!

Brendan Halpin,  Department of Sociology,  University of Limerick,  Ireland
Tel: w +353-61-213147 f +353-61-202569 h +353-61-338562; Room F2-025 x 3147
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