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Re: st: A query about sorting.


From   "Ashim Kapoor" <ashimkapoor@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: A query about sorting.
Date   Mon, 25 Aug 2008 18:06:26 +0530

gen v2 = -v /*to sort from highest to lowest*/
bys i (v2): gen var = _n


What do the above 2 lines do Maarten?

Thank you,
Ashim.

On Mon, Aug 25, 2008 at 5:58 PM, Maarten buis <maartenbuis@yahoo.co.uk> wrote:
> --- Ashim Kapoor <ashimkapoor@gmail.com> wrote:
>> I have a simple code to write.
>>
>> I have 6 variables v1, v2 , v3, v4 ,v5 , v6.
>>
>> I want to sort "according to each observation". That is , in the end
>> for each i I want , v1[i] < = v2[i] <=... v6[i].
>>
>> So I wrote a simple bubble for each row and then loop from 1 to _N.
>>
>> Now the problem is that this works but it's VERY VERY slow.
>
> This could be done using a combinatin of -reshape- and -by-, like in
> the example below. This should be faster.
>
> *--------------- begin example ---------------
> // create some random data
> drop _all
> set obs 10
> forvalues i = 1/3 {
>        gen v`i' = floor(10*uniform())
> }
>
> // do the sort
> list
> gen i = _n
> reshape long v, i(i) j(var)
> drop var
> gen v2 = -v /*to sort from highest to lowest*/
> bys i (v2): gen var = _n
> drop v2
> reshape wide v, i(i) j(var)
> drop i
> list
> *----------------- end example ----------------
> (For more on how to use examples I sent to the Statalist, see
> http://home.fsw.vu.nl/m.buis/stata/exampleFAQ.html )
>
> Hope this helps,
> Maarten
>
> -----------------------------------------
> Maarten L. Buis
> Department of Social Research Methodology
> Vrije Universiteit Amsterdam
> Boelelaan 1081
> 1081 HV Amsterdam
> The Netherlands
>
> visiting address:
> Buitenveldertselaan 3 (Metropolitan), room Z434
>
> +31 20 5986715
>
> http://home.fsw.vu.nl/m.buis/
> -----------------------------------------
>
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