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Re: st: How can I get the second last non-missing value?


From   Sergiy Radyakin <serjradyakin@gmail.com>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: How can I get the second last non-missing value?
Date   Wed, 12 Jun 2013 18:31:01 -0400

Besides loosing a variable it is also quite slow because of 2 reshapes
(and perhaps you have other variables in the data as well). I'd go to
Mata with this one, it is about 10 times faster and can probably still
be optimized:
r; t=1.72 18:25:22 vs r; t=16.88 18:25:39
Best, Sergiy

*** begin example ***
clear all

input id v1 v2 v3 v4 v5
  1 1  2  3  .  .
  2 1  2  .  .  .
  3 1  2  3  4  .
end

local exp=300000

expand `exp'

 mata

   void prelast() {
       V=.
       st_view(V,.,st_local("varlist"))
       R=.
       st_view(R,.,st_local("result"))

       for(i=1;i<=rows(V);i++) {

         for(j=0;j<cols(V);j++) {
           if (missing(V[i,cols(V)-j])==0) {
             // found last non-missing

             if (cols(V)-j-1<1) break;  //nothing before

             for(k=cols(V)-j-1;k>=1;k--) {
               if (missing(V[i,k])==0)
                 R[i,1]=V[i,k]
                 break;
             }

             break;
           }
         }
       }
   }

 end

 program define sergiy
   syntax varlist, result(string)

   quietly generate double `result'=.
   mata prelast()
 end

 program define rebecca
    quietly reshape long v, i(id) j(num)
    keep if ! missing(v)
    bys id (num): gen v6 = v[_N-1]
    quietly reshape wide v, i(id) j(num)
 end



 set rmsg on
   sergiy v1 v2 v3 v4 v5, result(r)
 set rmsg off


 clear

input id v1 v2 v3 v4 v5
  1 1  2  3  .  .
  2 1  2  .  .  .
  3 1  2  3  4  .
end

expand `exp'
replace id=_n

set rmsg on
  rebecca
set rmsg off

On Wed, Jun 12, 2013 at 5:01 PM, Rebecca Pope <rebecca.a.pope@gmail.com> wrote:
> Duygu,
> I think this will be easier with your data in long form.
>
> *** begin example ***
> clear
> input id v1 v2 v3 v4 v5
>   1 1  2  3  .  .
>   2 1  2  .  .  .
>   3 1  2  3  4  .
>  end
>
> reshape long v, i(id) j(num)
> keep if ! missing(v)
> bys id (num): gen v6 = v[_N-1]
> list, noobs clean
> reshape wide v, i(id) j(num)
> list, noobs clean
>
> *** end ***
>
> In this case, you lose v5, but presumably in your real data that
> variable is not universally missing. If you don't have a constant
> prefix for the variables in your dataset, you might want to check out
> -rename- and look at the methods for renaming groups. Standing advice:
> test this on a copy of your data rather than the original data.
>
> Regards,
> Rebecca
>
> On Wed, Jun 12, 2013 at 3:27 PM, duygu yıldırım <dyg_math@hotmail.com> wrote:
>> Hello everyone,
>>
>> I use a cross-sectional individual level data set. I want to ask if there is a way that I can create a variable which consists the second last non-missing value within observations?
>>
>> for example;
>>
>> id v1 v2 v3 v4 v5
>>  1 1  2  3  .  .
>>  2 1  2  .  .  .
>>  3 1  2  3  4  .
>>
>> So the variable that I want to create is;
>>
>> id  v6
>> 1   2
>> 2   1
>> 3   3
>>
>> I can get the last non-missing value within observation by using the rowlast command, but I also need the one just before the last one.
>>
>> Thank you all very much for any help,
>>
>> Duygu.
>>
>> *
>> *   For searches and help try:
>> *   http://www.stata.com/help.cgi?search
>> *   http://www.stata.com/support/faqs/resources/statalist-faq/
>> *   http://www.ats.ucla.edu/stat/stata/
>
> *
> *   For searches and help try:
> *   http://www.stata.com/help.cgi?search
> *   http://www.stata.com/support/faqs/resources/statalist-faq/
> *   http://www.ats.ucla.edu/stat/stata/

*
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*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/faqs/resources/statalist-faq/
*   http://www.ats.ucla.edu/stat/stata/


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