st: recording the first/last non-missing/missing values position

[Qunzi Zhang <zhangqunzi@googlemail.com>]

Dear All,
I have a dataset as below

date          firm 1   firm2    firm3 .....(permno as identifer index for firm)
1970Jan01   1         2      nan
1970Jan02   1         2      nan
..........................................
1990Jan01   1        2        4
1990Jan02   1        2        4

.........................................
1990Jan01   1      nan       nan
1990Jan02   1      nan       nan


I would like to store the time/row index for the first(last) nan value and
the first(last) non-nan value in this data set. Can anyone give me an
example about how to do this in the do file?

Thanks
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