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Re: st: Loop year variable


From   emanuele mazzini <madsoenistata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Loop year variable
Date   Mon, 22 Oct 2012 11:05:28 +0200

Many thanks Nick. That worked well in the subsample I showed you.
However, in my general sample I do not get as many as changes as I
thought.

I typed the following:

bysort iso_o iso_d year: gen date_won = year if FT_A > FT_B | FT_A<FT_B
by iso_o iso_d year: replace date_won = date_won[_n-1] if missing(date_w)

that seems correct to me, but I only obtain 14 real changes, that are
a way too low. That seems actually very strange to me, why I can't get
the replace? May it be due to the structure of the dataset? I mean,
even though it is not a panel in the proper sense, because I can have
more than 1 observation per year, that should not be a matter of
concern, because the date_won variable always takes the same value,
doesn't it?

Many thanks in advance for your help,

Regards,

Emanuele.



2012/10/22 Nick Cox <njcoxstata@gmail.com>:
> See for technique here
>
> 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/missing.html
>
> bysort iso_o iso_d (year) : gen datewon = year if !missing(FT_A, FT_B)
> & FT_A > FT_B
> by iso_o iso_d : replace datewon = datewon[_n-1] if missing(datewon)
> gen yrs_won = date - datewon
>
> Nick
>
> On Sun, Oct 21, 2012 at 10:37 PM, emanuele mazzini
> <madsoenistata@gmail.com> wrote:
>> Ok, let's ignore this additional issue for the moment. I can be
>> clearer I guess with the following example:
>>
>>  +---------------------------------------------------------------------+
>>      | year   iso_o   iso_d   team_A       team_B   FT_A   FT_B   date_won |
>>      |---------------------------------------------------------------------|
>>   1. | 1982     ITA     DEU    Italy   Germany FR      3      1       1982 |
>>   2. | 1983     ITA     DEU                            .      .          . |
>>   3. | 1984     ITA     DEU                            .      .          . |
>>   4. | 1985     ITA     DEU                            .      .          . |
>>   5. | 1986     ITA     DEU                            .      .          . |
>>      |---------------------------------------------------------------------|
>>   6. | 1987     ITA     DEU                            .      .          . |
>>   7. | 1988     ITA     DEU                            .      .          . |
>>   8. | 1989     ITA     DEU                            .      .          . |
>>   9. | 1990     ITA     DEU                            .      .          . |
>>  10. | 1991     ITA     DEU                            .      .          . |
>>      |---------------------------------------------------------------------|
>>  11. | 1992     ITA     DEU                            .      .          . |
>>  12. | 1993     ITA     DEU                            .      .          . |
>>  13. | 1994     ITA     DEU                            .      .          . |
>>  14. | 1995     ITA     DEU                            .      .          . |
>>      +---------------------------------------------------------------------+
>>
>> As you can see, the variable date_won is =1982 only for the year in
>> which the match was played. Now, I would like to generate a new
>> variable that would tell me how many years have gone by since Italy's
>> last won (e.g, =0 for 1982, =1 for 1983, =2 for 1984, etc.).
>> As I said, I tried with: gen yrs_won=year-date_won but this is the result:
>>
>>   +---------+
>>      | yrs_won |
>>      |---------|
>>   1. |       0 |
>>   2. |       . |
>>   3. |       . |
>>   4. |       . |
>>   5. |       . |
>>      |---------|
>>   6. |       . |
>>   7. |       . |
>>   8. |       . |
>>   9. |       . |
>>  10. |       . |
>>      |---------|
>>  11. |       . |
>>  12. |       . |
>>  13. |       . |
>>  14. |       . |
>>      +---------+
>>
>> As you can see, such command doesn't produce the expected result. That
>> explains why I was looking for a way to expand the value of date_won
>> for all cells. I thought that was the reason for the command not to
>> work. Do you have any suggestion for overcoming my problem?
>>
>> Thank you in advance,
>>
>> Regards,
>>
>> E.M.
>>
>>
>>
>>
>> 2012/10/21 Nick Cox <njcoxstata@gmail.com>:
>>> I gathered from your original posting that you had yearly data. I
>>> understand that matches may be more frequent than yearly, but I can't
>>> advise further without seeing what your data look like as the trade
>>> data and match data are not obviously compatible.
>>>
>>> Nick
>>>
>>> On Sun, Oct 21, 2012 at 1:00 PM, emanuele mazzini
>>> <madsoenistata@gmail.com> wrote:
>>>> Dear Mr Cox,
>>>>
>>>> thank you for your reply. The point, however, is that I cannot declare
>>>> my dataset to be time-series (how would like but I cannot) due to the
>>>> fact that some matches may take place once, twice or even more times
>>>> in the same year. That is why I was looking form a manual command. I
>>>> may better handle this first? And how can I do that in your opinion?
>
>
> 2012/10/21 Nick Cox <njcoxstata@gmail.com>:
>>>>> This should yield to a treatment in terms of spells in the sense of
>>>>> -tsspell- (SSC) and of
>>>>>
>>>>> SJ-7-2  dm0029  . . . . . . . . . . . . . . Speaking Stata: Identifying spells
>>>>>         . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
>>>>>         Q2/07   SJ 7(2):249--265                                 (no commands)
>>>>>         shows how to handle spells with complete control over
>>>>>         spell specification
>>>>>
>>>>> Look at -tsspell- first; it is self-contained. That is, your panels
>>>>> are defined by country pairs (dyads) and the start of a spell is
>>>>> defined by a match taking place (or a particular result; I don't
>>>>> follow exactly what you want, e.g what about draws?). Then a variable
>>>>> defined by -tsspell- gives you sequence in spell. You may need to
>>>>> subtract 1.
>>>>>
>>>>> I don't see that loops are needed.
>>>>>
>>>>> Nick
>>>>>
>>>>> On Sun, Oct 21, 2012 at 12:07 PM, emanuele mazzini
>>>>> <madsoenistata@gmail.com> wrote:
>>>>>
>>>>>> I am not a new Stata user, but I have to admit I still encounter some
>>>>>> problems with writing loops. A loop may not be the solution to the
>>>>>> issue I am going to describe, but I thought it is tough.
>>>>>>
>>>>>> I do have a dataset where I have country-pair trade observations for
>>>>>> years 1950-2006 as well as another information, which is football
>>>>>> match result for some dyads. I therefore need to generate a variable
>>>>>> that indicates how many years are passed since the last won/lost of a
>>>>>> country versus another. Suppose FT_A and FT_B are the final results
>>>>>> for team A and B. I thought to generate a variable as follows:
>>>>>>
>>>>>> gen int date_won=year if FT_A>FT_B | FT_A<FT_B
>>>>>>
>>>>>> in order to get a variable that is = year for every observation I have
>>>>>> information about, which reports the year of the won/loss. I then
>>>>>> thought to generate another variable (let's say yrs_won) to tell me
>>>>>> how many years have gone by as follows:
>>>>>>
>>>>>> gen int yrs_won=year-date_won
>>>>>>
>>>>>> Unfortunately, I do not get what I want: the only value yrs_won
>>>>>> assumes is 0, but for all years from 1983 until 2006 I would like it
>>>>>> to be 1, 2,3 and so on.
>>>>>>
>>>>>> At the beginning I didn't realize the problem, now it may be occur due
>>>>>> to the fact that date_won = year only for the year in which the match
>>>>>> was played. I guess I need to do something such as writing a loop to
>>>>>> let it spread over all cells of such variable, but I don't really know
>>>>>> how to make it. Does anyone of you has any suggestion?
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