Re: st: Calculating an Index

["Pavlos C. Symeou" <p.symeou@gmail.com>]

Dear Nick,

thank you the advice. I 've just ordered Kit Baum's book and 
started looking into the Mata reference manual that comes with 
Stata. But before I manage to reach a satisfactory level of 
programming competence that will allow me to deal with this and 
future problems I would appreciate it if for this time you could 
help me with the solution. Hopefully, this will be the last time I 
have to ask for assistance:)

Best wishes,

Pavlos

On Δευτέρα, 23 Ιανουάριος 2012 11:51:50 πμ, Nick Cox wrote:
> This has the same flavour as the previous problem so you should be
> able to adapt the previous solutions, or whichever one you adopted.
>
> My own view implicit in
>
> http://www.stata.com/statalist/archive/2012-01/msg00428.html
>
> is that your problem is very awkward without Mata and much less
> awkward with it. So, that advice would require you to learn more 
> about
> Mata and I really can't give enough detail in a posting to 
> explain all
> that you need to know. I'd recommend that you study Kit Baum's
> excellent book
>
> http://www.stata.com/bookstore/stata-programming-introduction
>
> and William Gould's authoritative columns on Mata matters in the 
> Stata
> Journal in addition to [M].
>
> Nick
>
> On Sun, Jan 22, 2012 at 9:05 PM, Pavlos C. 
> Symeou<p.symeou@gmail.com> wrote:
> > Dear Statlisters,
> >
> > Nick and Antonios kindly responded to a similar problem I 
> > encountered last
> > week. I hope I can also find some assistance with the following 
> > problem
> > which is a bit more complex. I don't know much about programming 
> > (e.g. using
> > mata) I would appreciate it if you could explain your code so 
> > that I can
> > adjust it in future problems. This way I will avoid to annoy you 
> > with
> > similar problems.
> >
> > Here it goes. I have data for a number of firms for multiple 
> > years per firm.
> > Each firm operates in a number of markets each year. A market's 
> > identifier
> > is denoted by a 3-digit number. I want to calculate a new 
> > variable "index"
> > as follows:
> >
> > 1) for each company-year I take the sales_ratio of each market 
> > and multiply
> > it with each other market's sales ratio:
> >
> > a) If the identifiers of the two markets are the same, then I 
> > multiply their
> > product with 1.
> > b) If the identifiers of the two markets have the same first 2 
> > digits (i.e.
> > they differ in the 3rd digit), then I multiply their product with 2.
> > c) If the identifiers of the two markets have the same first 
> > digit but
> > differ in all others, then I multiply their product with 3.
> > d) If the identifiers of the two markets differ in the first 
> > digit, then I
> > multiply their product with 4.
> >
> > The "index" variable equals the sum of a, b, c, and d.
> >
> > From the example data below, the Index for Firm 1 in Year 1996 
> > should be:
> > (0.071 * 0.14 * 4) + (0.071 * 0.071 * 4) + (0.071 * 0.29 * 4) + 
> > (0.14 *
> > 0.071 * 3) + (0.14 * 0.29 * 3) +(0.071 * 0.29 * 2) = 0.335
> >
> > firm_id year market sales_ratio
> > 1 1996 262 .071
> > 1 1996 349 .14
> > 1 1996 353 .071
> > 1 1996 357 .29
> > 1 1997 382 .36
> > 1 1997 733 .071
> > 1 1997 262 .5
> > 1 1997 353 .5
> > 1 1998 349 .15
> > 1 1998 357 .31
> > 1 1998 365 .077
> > 1 1998 382 .38
> > 1 1998 733 .077
> > 2 1996 349 .13
> > 2 1996 357 .27
> > 2 1996 365 .067
> > 2 1996 366 .067
> > 2 1996 371 .067
> > 2 1996 382 .33
> > 2 1996 733 .067
>
>
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