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Re: st: How to speed up loop


From   Ulrich Kohler <kohler@wz-berlin.de>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: How to speed up loop
Date   Wed, 15 Sep 2004 18:39:25 +0200

The following is a complete different approach --- but I think it works (not 
tested), and I bet that it is faster. It requires writing to the disk and 
sorting, but there is no loop at all:

. sort hhid mlineno
. save 11, replace

. keep hhid lineno age
. ren lineno mlineno
. ren age mage
. sort hhid mlineno
. save 12, replace

. use 11
. merge hhid mlineno using 12, nokeep

many regards
uli

Friedrich Huebler wrote:
> I am looking for advice to speed up a loop. The loop determines
> characteristics of other household members in household survey data
> and is taken from this Stata FAQ:
>
> http://www.stata.com/support/faqs/data/members.html
>
> The data has the variables hhid (household ID), lineno (line number
> of household member), age, and mlineno (mother's line number).
>
> hhid    lineno       age   mlineno
>    1         1        32         .
>    1         2        30         .
>    1         3         5         2
>    2         1        68         .
>    2         2        41         1
>    2         3        40         .
>    2         4        17         3
>    2         5        14         3
>
> The following code creates the variable mage with the mother's age.
>
> gen byte mage=.
> sum lineno, meanonly
> forvalues i = 1/`r(max)' {
>   gen byte tag = 1 if lineno==`i'
>   bysort hhid: egen byte iage = max(tag*age)
>   replace mage=iage if mlineno==`i'
>   drop tag iage
>   }

If mlineo is either missing or a valid line number:

by hhid (mlineno): gen mage = age[mlineo[1]]


> I tried changing -bysort hhid- to -by hhid- but the time needed for
> the loop is the same. Running the loop -quietly- also makes no
> difference. Can anything be done to make this loop go faster?
>
> Thank you,
>
> Friedrich Huebler
>
>
>
>
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-- 
kohler@wz-berlin.de
+49 (030) 25491-361


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