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Re: st: Double loop over unbalanced panel


From   Fernando Luco <flucoestatalist@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Double loop over unbalanced panel
Date   Sat, 3 Nov 2012 11:54:58 -0500

Thanks Sylvain and Nick, that worked perfectly.

Fernando

On Sat, Nov 3, 2012 at 4:12 AM, Nick Cox <njcoxstata@gmail.com> wrote:
> I agree with Sylvain. Apart from a twist which does not make the Stata
> code much more difficult, this looks like a standard problem discussed
> in an FAQ
>
> FAQ     . . . . . . . . . . . . . . . . . . . . . . . Replacing missing values
>         . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
>         2/03    How can I replace missing values with previous or
>                 following nonmissing values?
>                http://www.stata.com/support/faqs/data-management/replacing-missing-values/
>
> On Sat, Nov 3, 2012 at 5:53 AM, WEBER Sylvain <sylvain.weber@unine.ch> wrote:
>
>> I think you don't need any loop. - by - can be used instead.
>> Try
>> bysort id (t): replace chc=(chc[_n-1]*ph+cont)/p if mi(chc)
>>
>> Note that the - if mi(chc) - condition is very important. Otherwise, you would replace all values of chc; not only missing values.
>
> Le 2 nov. 2012 à 14:00, "Fernando Luco" <flucoestatalist@gmail.com> a écrit :
>
>>> The data and the formula look as follows
>>>
>>> input id t str1 ch p str1 chh ph cont con_c chc
>>> 1 1 "a" 2 "" . 1 0.5 1 1
>>> 1 2 "b" 3 "a" 4 3 1 .
>>> 1 2 "b" 3 "a" 4 3 1 .
>>> 1 3 "a" 1 "b" 2 2 2 .
>>> 1 4 "c" 4 "a" 3 3 .75 .
>>> 1 5 "d" 2 "c" 5 1 .5 .
>>> 2 3 "d" 2 "" . 1 1 2
>>> 2 4 "a" 3 "d" 3 3 1 .
>>> 2 5 "b" 1 "a" 2 2 2 .
>>> 2 6 "a" 2 "b" 2 1 .5 .
>>> end
>>>
>>> foreach k of numlist 1/2{
>>> foreach w of numlist 2/T_k{
>>> replace chc=(chc[`w'-1]*ph+cont)/p if _n==`w' & id==`k'
>>> }
>>> }
>
> On Fri, Nov 2, 2012 at 3:39 PM, Nick Cox <njcoxstata@gmail.com> wrote:
>
>>>> I think the best advice depends on what -formula()- is, which you
>>>> don't tell us.
>>>>
>>>> That said
>>>>
>>>> foreach of numlist ...
>>>>
>>>> in both your examples can be recast more simply as -forval- loops.
>
> On Fri, Nov 2, 2012 at 8:12 PM, Fernando Luco <flucoestatalist@gmail.com> wrote:
>
>>>>> I have an unbalanced panel and I need to do a loop over individuals and
>>>>> observations. My data looks as follows (I have other variables that are not
>>>>> represented in this example)
>>>>>
>>>>> id t  chc
>>>>> 1 1 .5
>>>>> 1 2 .
>>>>> 1 3 .
>>>>> 1 4 .
>>>>> 1 5 .
>>>>> 2 3 1
>>>>> 2 4 .
>>>>> 2 5 .
>>>>> 2 6 .
>>>>>
>>>>> What I want to do is, for each individual (id) to complete the values in
>>>>> chc according to a formula that depends on other variables. However, the
>>>>> number of times that each individual appears differs across individuals. I
>>>>> would like to do something such as
>>>>>
>>>>> foreach k of numlist 1/2 { /*the 2 has to be changed to the total number of
>>>>> individuals*/
>>>>> foreach w of numlist 2/T_k { /* where T_k corresponds to the number of
>>>>> times individual 2 appears*/
>>>>> replace chc=formula(`w')
>>>>> }
>>>>> }
>>>>>
>>>>> I don't know how to define T_k in the correct way such that it varies
>>>>> across individuals (so 5 for individual 1 and 4 for individual 2).
>
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