RE: st: Re: [question on -gammafit- and -pgamma-]

["Kieran McCaul" <Kieran.McCaul@uwa.edu.au>]

(1) get rid of the comma after the gammafit and put the -if- on the same line.
    gammafit y if group == `i'
(2) the matrix "results" is not the same as the matrix "Results".  Pick one name or the other.
(3) You need to preface the matrix assignments with the command -matrix-.

 

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Peter Maclean
Sent: Sunday, 6 March 2011 9:27 AM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: Re: [question on -gammafit- and -pgamma-]

I tried use the following commnds:

matrix results=J(10,3,.)
egen group = group(n) 
su group, meanonly 
forval i = 1/`r(max)' { 
  gammafit y, 
    if group == `i' 
    Results(`i',1)=e(alpha)
    Results(`i',2)=e(beta)
    results(`i',3)=e(alpha)*e(beta)
}

I am still getting the following error

{ required
r(100); and it the results is for all observations. 
Peter Maclean
Department of Economics
UDSM 



----- Original Message ----
From: Nick Cox <njcoxstata@gmail.com>
To: statalist@hsphsun2.harvard.edu
Sent: Sat, March 5, 2011 5:14:01 PM
Subject: Re: st: Re: [question on -gammafit- and -pgamma-]

Start with

-help foreach-

-help forval-

If necessary, continue with

SJ-2-2  pr0005  . . . . . .  Speaking Stata:  How to face lists with fortitude
        . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
        Q2/02  SJ 2(2):202--222                                (no commands)
        demonstrates the usefulness of for, foreach, forvalues, and
        local macros for interactive (non programming) tasks

FAQ    . . . . . . . . . . Making foreach go through all values of a variable
        . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
        8/05    Is there a way to tell Stata to try all values of a
                particular variable in a foreach statement without
                specifying them?
                http://www.stata.com/support/faqs/data/foreach.html

On Sat, Mar 5, 2011 at 10:25 PM, Peter Maclean <pmaclean2011@yahoo.com> wrote:
> Thanks Nick.
> My question was actually setting up a loop over a group and save the results.
> The number of group (n) is 600.
> Hope you can help on that.
> Peter Maclean
> Department of Economics
> UDSM
>
>
>
> ----- Original Message ----
> From: Nick Cox <njcoxstata@gmail.com>
> To: statalist@hsphsun2.harvard.edu
> Sent: Sat, March 5, 2011 1:16:33 PM
> Subject: st: Re: [question on -gammafit- and -pgamma-]
>
> It is always helpful to specify a subject for your email.
>
> This question refers to -gammafit- and -pgamma- from SSC, which are
> user-written programs.
> Statalist etiquette is to explain where user-written programs referred
> to come from.
>
> Peter quotes the syntax
>
> by n:gammafit y, level(95)
>
> which -gammafit- supports. However, as is standard with -by:- support,
> this syntax is of limited use for _saving_ results, as after the
> first, each invocation of -gammafit- stomps over the previous set of
> saved results, so although parameter estimates are displayed in turn,
> only the last such set is present in memory once all are done.
>
> Peter correctly reports that -pgamma- does not support the -by()-
> option (nor does it support the -by:- prefix).
>
> I am not aware that Stata supports doubly subscripted variables.
> Perhaps Peter means a Stata or Mata matrix.
>
> To get results for different groups and put them together, Peter has
> to arrange that himself. But this code shows that the steps are
> simple.
>
> sysuse auto, clear
> matrix results = J(2,2,.)
> gammafit mpg if foreign
> matrix results[1,1] = e(alpha)
> matrix results[1,2] = e(beta)
> pgamma mpg if foreign, gen(tp1 ep1)
> gammafit mpg if !foreign
> matrix results[2,1] = e(alpha)
> matrix results[2,2] = e(beta)
> pgamma mpg if !foreign, gen(tp2 ep2)
> matrix rownames results = Foreign Domestic
> matrix colnames results = alpha beta
> matrix li results
> scatter tp1 ep1 || scatter tp2 ep2 , legend(order(1 "Foreign" 2 "Domestic"))
>
> For a group variable with many more than 2 classes, it would be better
> to set up a loop over the groups.
>
> The help for -gammafit- includes a link to the help for -maximize-,
> which explains how to set initial values.
>
> Nick
>
> On Sat, Mar 5, 2011 at 4:47 PM, Peter Maclean <pmaclean2011@yahoo.com> wrote:
>
>> I am new is Stata modelling.
>> I am running the following model:
>>
>> by n:gammafit y, level(95)
>> pgamma y, gen(g_p e_p)
>>
>> where n is  a group variable.
>> I would like to save the estimated parameters by gammafit
>>(alpha,beta,alpha+beta
>> and lower and upper limit of both alpha and beta) in a variable 
'result(n,j).'
>>
>>
>> Also, I would like pgamma to estimate the probabilities (g_p and e_p) by
>> variable n.
>> The pgamma module does not accept the 'by' option. In addition, is there a 
way
>> to give starting values for the gammafit module?
>

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