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st: RE: Indexing Question


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Indexing Question
Date   Mon, 29 Aug 2005 17:04:27 +0100

Dear Kelly: 

A very similar question was asked by Fuaad last 
week from the same email address. 

With no missing values, this sounds like 

bysort (date) : gen pc_change = 100 * (X[_N] - X[1]) / X[1] 

Nick 
n.j.cox@durham.ac.uk 

kelly johnson
 
> 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.
> 
>         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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