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Re: st: How to convert Daily data with gaps to weekly?


From   "Joao Ricardo F. Lima" <jricardofl@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: How to convert Daily data with gaps to weekly?
Date   Thu, 8 Mar 2012 10:07:58 -0300

Hi Nick,

thanks a lot for your help.

Joao Lima

Em 8 de março de 2012 09:46, Nick Cox <n.j.cox@durham.ac.uk> escreveu:
> It is vital to realise that Stata's -week()- function, etc. and also its week display format do _not_ relate exactly to the method here and will just lead to messes. This should be clear from careful study of my Stata Tip cited in emails cited here.
>
> I think there is one (and quite possibly only one) to proceed here, to map weeks to successive integers and -tsset- in terms of that counter.
>
> Note that -egen, group()-, suggested earlier in the thread, is _dangerous_ here as it cannot be smart about weeks for which there are no data at all.
>
> The following indicates some technique. -labmask- must be installed from the SJ site.
>
> clear
> set obs 366
> gen time = mdy(12,31,2011) + _n
> format time %tdd_n_CY
> l in 1
> drop if runiform() > 0.9
> gen sunday = time - dow(time)
> gen s_sunday = string(sunday, "%dd_n_CY")
> gen week = floor(sunday/7)
> labmask week, values(s_sunday)
> tab week
> tsset week
>
>
> Nick
> n.j.cox@durham.ac.uk
>
> Joao Ricardo F. Lima
>
> Hi Nick,
>
> thanks a lot for the answer. The use of -dow()- and -collapse- was
> what I was looking for. With this solved, another problem appeared.
> How to -tsset- the data? I cant just -format- and -tsset- the variable
> "sunday" how weekly, as you can see below:
>
> ********************begin example******************
> clear
> input str11 date price_guava
> 7-Oct-2004      9.00
> 10-Oct-2004     8.00
> 12-Oct-2004     8.00
> 14-Oct-2004     7.00
> 17-Oct-2004     6.00
> 19-Oct-2004     6.00
> 21-Oct-2004     7.00
> 24-Oct-2004     7.00
> 26-Oct-2004     8.00
> 28-Oct-2004     9.00
> 31-Oct-2004     9.00
> 2-Nov-2004      9.00
> 4-Nov-2004      10.00
> 9-Nov-2004      10.00
> 11-Nov-2004     10.00
> 14-Nov-2004     10.00
> 16-Nov-2004     9.00
> 18-Nov-2004     8.00
> 21-Nov-2004     8.00
> 23-Nov-2004     7.00
> 25-Nov-2004     7.00
> 28-Nov-2004     7.00
> 30-Nov-2004     7.00
> end
>
> gen eventtime=date(date, "DMY")
> gen sunday=eventtime-dow(eventtime)
> collapse price_guava, by(sunday)
>
> format sunday %tw
> tsset sunday, w
> ******************************end of example********************
>
> . tsset sunday, w
>        time variable:  sunday, 2274w20 to 2275w24, but with gaps
>                delta:  1 week
>
> I found a solution, however, not ellegant, but it runs. After the
> -collapse- line:
>
> ************
> local year=year(sunday[1])
> local week=week(sunday[1])
> gen time=w(`year'w`week')+_n-1
> format time %tw
>
> tsset time, w
> ***************
>
> Best Regards,
>
> Joao Lima
>
>
>
>
>
> Em 7 de março de 2012 06:01, Nick Cox <njcoxstata@gmail.com> escreveu:
>> Another way is to aggregate into weeks using date functions. The
>> easiest way I know to do this is to classify weeks by their starting
>> Sundays. -dow()- returns 0 for Sundays
>>
>> . di dow(mdy(3,4,2012))
>> 0
>>
>> and so
>>
>> gen dailydate = date(date, "DMY")
>> gen Sundays = dailydate - dow(dailydate)
>>
>> collapse ... , by(Sundays)
>>
>> The last presumes that what you in mind is something like averaging in
>> each week.
>>
>> Weeks have puzzled some users of Stata, even to the accusation of that
>> the implementation is  buggy in
>>
>> http://www.stata.com/statalist/archive/2012-02/msg01023.html
>>
>> For the good news, see
>>
>> http://www.stata.com/statalist/archive/2012-02/msg01027.html
>>
>> http://www.stata.com/statalist/archive/2012-02/msg01030.html
>>
>> and in turn the references they give, and so on.
>>
>> Nick
>>
>> On Wed, Mar 7, 2012 at 3:10 AM, William Pratt <williamrpratt@gmail.com> wrote:
>>> It depends on what your goal is. You can use tsfill to create weekend
>>> values, though you will have no data for those days. The other method
>>> is to use the group function within the egen command. This will create
>>> a value that you can use to ts or xt set your data, as well as
>>> generation lag variables.
>>>
>>> tsfill
>>>
>>> egen (new var) = group ( )
>>>
>>> On Tue, Mar 6, 2012 at 6:43 PM, Joao Ricardo F. Lima
>>> <jricardofl@gmail.com> wrote:
>>>> Dear Statalisters,
>>>>
>>>> I'm working with a time series of guava price like this:
>>>>
>>>> input str11 date preco_goi
>>>> 7-Oct-2004      9.00
>>>> 10-Oct-2004     8.00
>>>> 12-Oct-2004     8.00
>>>> 14-Oct-2004     7.00
>>>> 17-Oct-2004     6.00
>>>> 19-Oct-2004     6.00
>>>> 21-Oct-2004     7.00
>>>> 24-Oct-2004     7.00
>>>> 26-Oct-2004     8.00
>>>> 28-Oct-2004     9.00
>>>> 31-Oct-2004     9.00
>>>> 2-Nov-2004      9.00
>>>> 4-Nov-2004      10.00
>>>> 9-Nov-2004      10.00
>>>> 11-Nov-2004     10.00
>>>> 14-Nov-2004     10.00
>>>> 16-Nov-2004     9.00
>>>> 18-Nov-2004     8.00
>>>> 21-Nov-2004     8.00
>>>> 23-Nov-2004     7.00
>>>> 25-Nov-2004     7.00
>>>> 28-Nov-2004     7.00
>>>> 30-Nov-2004     7.00
>>>> end
>>>>
>>>> The time series is daily but with gaps. Thus, I can´t use the -dfgls-
>>>> command, for example and others TS commands.
>>>>
>>>> What can I do in this case? Can I convert the daily data with gaps to
>>>> weekly? Is there a better procedure to do the trick?
>
> *
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-- 
---------------------------------------------------------
João Ricardo F. de Lima
Pesquisador A - Economia Aplicada
Embrapa Semiárido
e-mail: joao.ricardo@cpatsa.embrapa.br
fone: +55 (87) 3866-3667
home-page: www.cpatsa.embrapa.br
----------------------------------------------------------

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