# Re: st: Indexing Question

 From Ulrich Kohler To statalist@hsphsun2.harvard.edu Subject Re: st: Indexing Question Date Mon, 29 Aug 2005 18:00:20 +0200

```. by id (date), sort: gen change = (X[_N]-X[1])/X[1] * 100

Uli

kelly johnson wrote:
> I have a question regading calculations and indexing. Below I have an
> except of a larrge data set. How can I calculate the percentage change in
> the variable X from the earliest date to the last date (e.g. in the case
> where id==1, the percentage change in X from 7/1/05-7/6/05). I want to do
> this by id for all my observations (i have thousands of obsevations and the
> date periods are of varying lengths...). I know it's of the 'by id:' type
> of statements, but I just can't get it right. Thank you.
>
> Kelly
>
>
>         date   id       X
>      7/1/05    1      .2
>      7/2/05    1      .3
>      7/3/05    1      .2
>      7/4/05    1      .1
>      7/5/05    1      .5
>      7/6/05    1      .6
>     6/16/05    2      .4
>     6/17/05    2      .4
>     6/18/05    2      .4
>     6/19/05    2      .2
>     6/20/05    2      .1
>     6/21/05    2      .3
>     6/22/05    2      .5
>     4/11/05    3      .2
>     4/12/05    3      .8
>     4/13/05    3      .7
>     4/14/05    3      .8
>     4/15/05    3      .2
>     4/16/05    3      .2
>     4/17/05    3      .3
>     4/18/05    3      .1
>     4/16/05    3      .5
> ...
>
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