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RE: st: RE: Changing positive values to negative in Stata


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: RE: Changing positive values to negative in Stata
Date   Thu, 20 Apr 2006 22:17:55 +0100

Now, joking aside, you are setting a bad 
example here. The condition 

scott == exp(1)^c(pi) 

is, in practice, only going to catch values of -scott- 
that were calculated that way. Equality means exactly 
identical values, down to the last bit. It's on 
a level with "I will marry someone nice who owns 2,345
books." The conditions, meant to specify a sweet scholar, 
in practice narrow the field rather too much. An 
inequality would be a better idea. 

Nick 
n.j.cox@durham.ac.uk 

Maarten buis
 
> Lets call this other variable which captures the common 
> charecteristics scott, and suzy has to be
> negative if scott is larger than 2 and less than pi or is 
> equal to e to the power pi. Than you
> would code:
> 
> replace suzy = -suzy if suzy > 0 & ( scott > 2 & scott < 
> c(pi) ) | scott == exp(1)^c(pi)
 
> --- Suzy <scott_788@wowway.com> wrote:
> 
> > Thanks Nick - I neglected to state that  have over 600 
> observations with 
> > all different positive values (as well as negative values 
> and missing 
> > values) within the subgroup of total observations of the 
> variable, so 
> > this code could be somewhat inefficient.  Also,  it is difficult to 
> > specify which observations, for example, by id  - thus  the 
> next best 
> > thing in this instance seems to be to sort by their common 
> > characteristic - which  is captured by another variable.
> > 
> > Nick Cox wrote:
> > 
> > >replace suzy = -suzy if suzy > 0 & <whatever> 
> > >
> > >So if suzy is positive, it is negated. The 
> > >crunch is specifying the extra condition <whatever> 
> > >that catches just the observations desired. 
> > >
> > >Sorting is a red herring here. So long as you 
> > >can specify which observations you want, sort order
> > >is immaterial. 
> > >
> > >Nick 
> > >n.j.cox@durham.ac.uk 
> > >
> > >Suzy
> > > 
> > >  
> > >
> > >>I have a continuous variable with positive, negative, and 
> zero values 
> > >>and also missing values(.). 
> > >>I would like to know if anyone has an easy Stata code/command 
> > >>to change 
> > >>just the positive values to a negative (change the sign: 
> 4.4567 to 
> > >>-4.4567) for just a particular subgroup of the total (n=661 
> > >>out of over 
> > >>N=4,000). Within this subgroup (which I can sort, but not by 
> > >>id) there 
> > >>already are a few appropriately negative values in place.

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