Re: st: reshape and overtime variation

[DTA <altruist81@gmx.de>]

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


-------- Original Message --------
Subject: Re: st: reshape and overtime variation
From: Nick Cox <njcoxstata@gmail.com>
To: statalist@hsphsun2.harvard.edu <statalist@hsphsun2.harvard.edu>
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
> njcoxstata@gmail.com
>
>
> On 13 November 2013 19:15, Nick Cox <njcoxstata@gmail.com> 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
> > njcoxstata@gmail.com
> >
> >
> > On 13 November 2013 18:54,  <altruist81@gmx.de> 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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