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Re: st: Creating a new variable with information from other observations


From   "Davide Cantoni" <davide.cantoni@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Creating a new variable with information from other observations
Date   Mon, 19 May 2008 13:38:30 +0200

Thank you, Teresio. That works fine.

More generally, could I ask you statalisters again about the last
doubt I expressed in my previous email, i.e.:

:: is there a way to run a "foreach" over all (numeric) values that a
given variable takes, without having to specify exactly the values
that this variable takes? Ok, I see, in most cases this would be a job
for "by(sort)", but I cannot help thinking that there are some cases
in which bysort does not help me -- for example when I want to run
more than one command, as I would do within the braces of
"foreach...", or when the units the loop runs over (the `X' in
"foreach X", so to speak) are used in some logical condition.

In brief: is there a way to create a numlist from the unique values
that a variable takes? Or how would you proceed?

Thanks,

Davide



2008/5/18 Teresio Poggio <terlist@gmail.com>:
> Dear Davide,
>
> from your dataset I'd build a just capitals dataset:
> - select just the capitals (drop if cityid !=capitalid)
> - in the new dataset keep just capitalid and latitude
> - rename latitude into latitude_capital
> - sort the data by capitalid and save it
>
> then open you original data set and sort it by capitalid,
> merge it with the new "just capital dataset" using capitalid as a key
> and the option uniqmaster
> (help merge for details)
>
> Hope this helps.
>
> Teresio
>
> On Sun, May 18, 2008 at 2:22 PM, Davide Cantoni
> <davide.cantoni@gmail.com> wrote:
>> Hello,
>>
>> I am having a rather intricate problem in creating a new variable in a
>> panel dataset, and I appreciate any help you could offer. I hope the
>> problem can potentially be of general interest.
>>
>> I have a panel dataset of cities and their characteristics in
>> different countries. I know the latitude of each one of these cities,
>> but now I want to create an additional variable reflecting the
>> latitude of the capital city of the country a given city lies in. So
>> for example: for the cities of New York, Chicago, etc., I want this
>> new variable to contain the latitude of Washington, DC.
>>
>> Here is a description of the dataset's structure: it is a panel in
>> long form, with cities in different countries, observed over different
>> years. Each city has a unique numeric identifier, "cityid". Then there
>> is a country identifier, called "countryid". Finally, there is a
>> variable that repeats the capital city's cityid for each city in a
>> given country, "capitalid". For instance, if the cityid of London was
>> 135, all cities in the dataset that are in the UK would get a value of
>> 135 in the variable "capitalid". Finally, there is a variable called
>> "latitude" that refelcts the latitude of each city.
>>
>> How would I now proceed to create this new variable, call it
>> "latitude_capital", by using the variables above?
>>
>> Basically, the problem I'm having is
>> - tell stata to look up for each city its capitalid
>> - browse the dataset until you find a city that has the cityid equal
>> to this capitalid
>> - find out the latitude of this capital city
>> - go back to the original city and replace "latitude_capital" with the
>> latitude you've just retrieved
>>
>> The additional problem I encounter while trying to construct something
>> with "foreach..." (that, at least, is what I was trying so far) is
>> that the values that the capitalid variable takes are of course not a
>> clean numlist (like "1(1)100"), but rather a sequence of numbers
>> without any regularity, such as 11 12 50 54 60 131... and so on.
>> Thanks for your suggestions!
>>
>> Davide Cantoni
>> *
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>>
>
>
>
> --
> ____________________________________________________
> dr. Teresio Poggio
> LaboR - Dipartimento di Sociologia e ricerca sociale
> UniversitÓ degli studi di Trento
> Piazza Venezia, 41
> 38100 Trento, Italy
> Tel +39 0461/881406
> fax: +39 0461/881348
>
> *
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>

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