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Re: st: RE: A query about min in stata


From   "Ashim Kapoor" <ashimkapoor@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: A query about min in stata
Date   Fri, 22 Aug 2008 21:27:58 +0530

Thank you,

I really appreciate this tip.

Ashim.

On 8/22/08, Nick Cox <n.j.cox@durham.ac.uk> wrote:
> Yes, the = sign has to be there. See help on -macro-. A generic example
> is `= exp' where exp is an expression to be evaluated on the fly.
> Without the = sign, Stata expects a local macro name.
>
> Consider
>
> `=`i'+9'
>
> The exp is `i' + 9.
>
> Consider now
>
> ``i'+9'
>
> Without the equals sign, Stata would see in this case 1+9, 2+9, etc. but
> they are not macro names, so the thing would fail.
>
> Nick
> n.j.cox@durham.ac.uk
>
> Martin Weiss
>
> Well, it calculates the endpoint of the rolling min calculation,
> depending
> on the index "i". To make Stata calculate, you put the equal sign in
> front
> of the mathematical expression. Not sure whether it has to be there, but
> I
> want to err on the safe side here...
>
> Ashim Kapoor
>
> What is that = doing in that statement starting with " qui " doing. It
> works. But why ?
>
> On Fri, Aug 22, 2008 at 4:30 PM, Martin Weiss
>
> > If that is supposed to be some kind of "rolling" estimation,
> >
> > *************
> > sysuse auto , clear
> > g rollingmin=.
> > forv i =1/65{
> > qui su mpg in `i'/`=`i'+9'
> > di in red "min in `i' to `=`i'+9': " r(min) _n
> > qui replace rollingmin = r(min) in `i'
> > }
> >
> > l rollingmin
> > *************
>
> Ashim Kapoor
>
> > I am trying to do the following : -
> >
> > I have a variable r. I want to create a variable m=min( r, r[_n-1],
> > ... ,r[_n-9])
> >
> > I guess I can use a while loop to do this but that is quite slow. An
> > alternative would be to define r0=r,r1=r[_n-1],..,r9=r[_n-9]
> > and then say m=rmin ( r0 r1 ... r9).
> >
> > My question is that is there a built in way in stata to do this ? like
> > say by using egen ?
>
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