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Re: st: reshape and overtime variation


From   DTA <[email protected]>
To   [email protected]
Subject   Re: st: reshape and overtime variation
Date   Wed, 13 Nov 2013 21:53:34 +0100

Thank you! Your response is - as always- very much appreciated and helpful!


-------- Original Message --------
Subject: Re: st: reshape and overtime variation
From: Nick Cox <[email protected]>
To: [email protected] <[email protected]>
Date: Wed Nov 13 2013 20:44:32 GMT+0100
This FAQ is also relevant

http://www.stata.com/support/faqs/data-management/listing-observations-in-group/
Nick
[email protected]


On 13 November 2013 19:15, Nick Cox <[email protected]> wrote:
Suppose you have a bundle of variables, that may or may not be
constant over time. Then

gen isconstant = .
gen ismissing = .

foreach v of var <varlist> {
     replace ismissing = missing(`v')
     bysort ismissing panel_id (`v') : replace isconstant = `v'[1] == `v'[_N]
     su isconstant, meanonly
     if r(min) == 1 {
            local NOTFIX `NOTFIX' `v'
    }
}

If variables are constant, then the first and last are always
identical after sorting. But you need to segregate missings. (This
assumes all missings are system missing, not any of .a ... .z.)

Or

foreach v of var <varlist> {
    egen panel_sd = sd(`v'), by(panel_id)
    su panel_sd, meanonly
    if r(min) == 0 {
         local NOTFIX `NOTFIX' `v'
    }
    drop panel_sd
}

If variables are constant, then their SD will be 0.


Nick
[email protected]


On 13 November 2013 18:54,  <[email protected]> wrote:
Der Stata-list-users,

I am working with a balanced panel dataset in long format (that also includes missing values). The dataset has more than 200 variables. Some of these variables vary over time, others do not.

I want to reshape the dataset into a wide format without loosing any information. For this purpose I would like to create a local -NOTFIX- which should only contain all variable names of variables that are (within all observation units) constant over time.

My ultimate aim is then to type: reshape wide `NOTFIX', i(unit_id) j(year)

My question: Can anyone provide a suggestion on how to create NOTFIX?

Many thanks!
Darjusch Tafreschi




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