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Re: st: First visit to clinic


From   Neil Shephard <[email protected]>
To   [email protected]
Subject   Re: st: First visit to clinic
Date   Mon, 20 Sep 2010 13:28:36 +0000

On Mon, Sep 20, 2010 at 1:24 PM, Paul O'Brien <[email protected]> wrote:
> i want to create a new variable with the date of the first visit of each patient:
>
> id              date            date_of_first_visit
> N-00-3558       07/04/2008      07/04/2008
> N-00-3558       09/04/2008      07/04/2008
> N-00-3558       14/05/2008      07/04/2008
> N-00-3563       05/06/2007
> N-00-3563       31/03/2010
> N-00-3565       05/06/2007
> N-00-3565       13/06/2008
> N-00-3565       13/06/2008
> N-00-3565       05/05/2009
> N-00-3565       04/03/2010
> N-00-3583       09/09/2008
> N-00-3583       27/05/2009
>
> i know this should be easy by i am having trouble using n_1
>
> i have tried:
> .sort date
> .by id, sort: gen visit=_n==1
>
> but the latter does not have the date in order, only id.

bysort id (date) gen date_of_first_visit = date[1]

should do the trick.

Neil

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