st: RE: Looping with -qreg-

["STANEVA A. (497186)" <A.V.STANEVA.497186@swansea.ac.uk>]

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 normal qreg, ignoring all this manipulations.
>>

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