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Re: st: slow execution of duplicates drop varlist, force

From   Nick Cox <>
Subject   Re: st: slow execution of duplicates drop varlist, force
Date   Tue, 26 Jun 2012 16:30:56 +0100

You can see for yourself what -duplicates- does by looking at the code.

. viewsource duplicates.ado

There is some scaffolding and some extra stuff that supports other
things that -duplicates- can do. It is not optimised for the case in
which you know that you want to -drop- in the way that you do; in
particular it is designed to protect people losing information by
checking what's what.

I am surprised at "much faster", however.


On Tue, Jun 26, 2012 at 4:16 PM, Kristoffer Milonas
<> wrote:

> I wonder why the syntax duplicates drop varlist,force takes so long time on large datasets compared to doing it manually.
> Suppose for instance that varlist is groupvar1 groupvar2 ... groupvark. It seems to me that I can then drop duplicates manually by typing
> sort groupvar1 ... groupvark
> keep if groupvar1!=groupvar1[_n-1] | ... | groupvark!=groupvark[_n-1].
> The latter is much faster when I try (using both versions 10 and 11 of Stata). Am I missing some finer points that the duplicates drop command takes into account?
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