Thank you, Nick, for the quick help. I'm still missing something.
I decided that I didn't care, for this exercise, whether data in
memory would be lost. So I threw out the "preserve" part and I
attempted two things, with data properly xtset ahead of time:
1) xtdata, fe
2) xtdata, fe clear
Their outcomes were:
1) no; data in memory would be lost r(4); -- fair enough
2) no observations r(2000);
This is strange, because the observations are all there, I can see
them: 3660, for a strongly balanced panel with t[1:30]. Usually I get
this r(2000) error when the data set in memory is empty.
Gabi
On Thu, Dec 3, 2009 at 1:30 PM, Nick Cox <[email protected]> wrote:
> My guess is that -xtdata- has no idea that you have just typed
> -preserve-.
> I don't think -preserve- has any side-effect in terms of setting a flag
> that Stata can now be destructive willy-nilly.
>
> Why should it?
>
> -xtdata- is just being conservative in your best interests. You just
> need to spell out that you know that you are being sensible. Specify the
> -clear- option.
>
> (I answered this by looking at the help for Stata 11, but it's likely
> that the answer is the same for Gabi.)
>
> Nick
> [email protected]
>
> Gabi Huiber
>
> I have a balanced panel of weekly lottery ticket sales.
>
> I am trying to do a bit of exploratory analysis, and I attempted a
> within scatterplot as done in Micreconometrics using Stata, by Cameron
> and Trivedi, Stata Press 2009, at p. 243. But I get a strange error
> message:
>
> . preserve
> . xtdata, fe
> no; data in memory would be lost
> r(4);
>
> Why would I be warned about data loss after preserve? This is Stata
> 9.2 MP. I would appreciate any ideas.
>
>
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