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st:why -recode-takes longer than -replace-


From   Amanda Fu <mandy.fu1@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st:why -recode-takes longer than -replace-
Date   Sun, 27 Jun 2010 16:10:47 -0400

Dear Statalisters,

I am just curious about a fact noticeable when I use -recode- (1 as
following) or -replace- (2 as following)  to recode all the variables
in a data set (size :  52,996,616) using Stata 10.1 SE: the recode
command  takes much longer than replace. I was wondering what causes
the speed difference and if the speed difference implies for large
data set it would be better to use replace instead of recode.

1.  slower
.recode _all (8=.) (9=.)

2. faster
foreach v of varlist * {
.replace `v'=. if `v'==8 | `v'==9
}
end

Thanks for your time!

Sincerely,
Amanda
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