Re: st: RE: Looping with -qreg-

[Nick Cox <njcoxstata@gmail.com>]

So it seems you want a set of quantile regressions for fractions 0.01 
(0.01)0.99 but with the same intercept. Wow!

I would suggest being clearer on what you tried with -constraint- and  
why it didn't solve the problem.

Nick

On 19 Jan 2012, at 12:03, "STANEVA A. (497186)" <A.V.STANEVA.497186@swansea.ac.uk 
> wrote:

> Thanks Nick for your comments.
> I did try with constraint option but didn't get what I need.  
> Basically my problem is to estimate the last qreg with the new  
> constant term  (u99) 'plug' in the model. There is not noncons  
> option in qreg.
> Best wishes
> Anita
>
> ________________________________________
> From: owner-statalist@hsphsun2.harvard.edu [owner- 
> statalist@hsphsun2.harvard.edu] on behalf of Nick Cox  
> [njcoxstata@gmail.com]
> Sent: 19 January 2012 11:52
> To: statalist@hsphsun2.harvard.edu
> Subject: Re: Looping with -qreg- [was: Re: st: Thread-Index:  
> AczWnG9bfd8mYxtIRa2sdn3BOpo1xA==]
>
> Also, it sounds as if you want to constrain your -qreg-, which makes
> me feel queasy even contemplating the idea from a distance, but if so
> that implies trying -constraint-.
>
> Nick
>
> On Thu, Jan 19, 2012 at 11:45 AM, Nick Cox <njcoxstata@gmail.com>  
> wrote:
> > Please use informative titles (subjects) for your postings. Many
> > people delete posts unread if they have weird titles.
> >
> > There are problems at various levels with your code.
> >
> > 1. The line
> >
> > local `b' = scalar(u99)
> >
> > looks like a mistake. If local b _was_ previously defined, then you
> > need to refer to what this line defines as ``b''.
> >
> > 2. But you don't refer either to `b' or to ``b'' after defining it,  
> > so
> > all you have done is defined something but never used it.
> >
> > 3. If local b was not previously defined, this line would not work.
> > But that is not what you are reporting, so my guess is that a "local
> > b" is defined earlier in your code.
> >
> > 4. If you have a scalar, there is no obvious need to put it into a
> > local for what you want to do.
> >
> > 5. I don't understand what you want to do, but you are changing
> > results, not instructions. Later runs of -qreg- pay no attention to
> > e(b) produced by earlier runs of -qreg-.
> >
> > 6. -matrix b- and -local b- are completely different entities.
> >
> > Nick
> >
> > On Thu, Jan 19, 2012 at 11:21 AM, STANEVA A. (497186)
> > <A.V.STANEVA.497186@swansea.ac.uk> wrote:
> >
> > > Can someone help me with this loop in a qreg?
> > > This first line works ok!
> > >
> > > forval i = 1/99 {
> > > local q = `i'/100
> > > quietly qreg $y $x if public==0, quantile(`q') nolog
> > > matrix b = e(b)
> > > matrix b[1, colnumb(b,"_cons")] = scalar(u99) /*I get the constant  
> > > and replace it with the scalar u99, that I want/
> > > }
> > >
> > > The problem comes here. I want the replaced u99 to be included in  
> > > my qreg and then to get the predictions based on that regression:
> > >
> > > forval i = 1/99 {
> > > local q = `i'/100
> > > local `b’= scalar (u99)
> > > quietly qreg $y $x if public==0, quantile (`q') nolog
> > > predict xb if public==0
> > > preserve
> > > keep if xb~=.
> > > restore
> > > }
> > > However, there is a problem in the line local`b'=scalar(u99), it  
> > > seems stata doesn’t replace the _cons with the u99. It runs norm 
> > > al qreg, ignoring all this manipulations.

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