. 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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