RE: st: gsort issue

["Brian P. Poi" <bpoi@stata.com>]

On Thu, 5 Jul 2007, Fred Wolfe wrote:

...

> I remember (from the old days) that -gsort- didn't set the sort order. But 
> sometime ago it was changed, or was it? gsort help says that it "... differs 
> from sort in that sort produces ascending-order arrangements only."
>
> However, the following code produces ?unexpected results:
>
> . sort age duration
> . local sortorder : sort
> . di "sort order is `sortorder'"
> sort order is age duration
>
> . gsort -age duration
> . local sortorder : sort
> . di "sort order is `sortorder'"
> sort order is
...
> So it seems that gsort sets the sort order only in ascending sorts. Either 
> that or the reported output is wrong.
-gsort- will only set the sort order flag when it sorts in ascending 
order.  Internally Stata considers the data to be sorted in ascending 
order or not sorted at all.  Stata commands that require sorted data need 
the data to be in ascending order.  For example, the -by:- prefix requires
that the data be sorted in ascending order of the by variable(s).

If you -gsort- a variable or variables in ascending order, the sort order 
flag gets set because other Stata commands and features that rely on the 
data being sorted can then work.

But if you -gsort- in descending order, as far as Stata commands that 
require the data be sorted are concerned, your data are not sorted because 
they are not sorted in ascending order.  So in this case -gsort- does not 
set the sort order flag.

   -- Brian Poi
      bpoi@stata.com


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