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

 From "Nick Cox" To 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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