st: "no; data in memory would be lost" warning after preserve?

[Gabi Huiber <ghuiber@gmail.com>]

Hello all,

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.

Thank you,

Gabi Huiber
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