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st: RE: RE: Trouble with `=`_N'-1'


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: RE: Trouble with `=`_N'-1'
Date   Mon, 1 Sep 2008 16:50:37 +0100

Just to underline Martin's analysis: the reference `_N' would be
appropriate if _N were the name of a local macro, but _N is not a local
macro. 

Nick 
n.j.cox@durham.ac.uk 

Martin Weiss

Stata does not know what to do about `_N', so it evaluates to nothing.
The
whole -in- statement evaluates to - in -1 - which denotes the last
observation. Say -replace line = 5 in `=_N-1'- and it works fine. Now _N
is
well defined and the expression evaluates to the desired value. Note
that
you could have put - in -2 - to begin with, and would have saved
yourself
the trouble...

Ashim Kapoor

I wish to make a change in the 2nd last observation.

so I have : replace line = 5 in `=`_N'-1'

But this change the LAST observation! Am I doing something wrong?

funnily replace line = 5 if _n==_N-1 works fine!


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