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

From   "Martin Weiss" <>
To   <>
Subject   st: RE: RE: RE: Trouble with `=`_N'-1'
Date   Mon, 1 Sep 2008 18:02:57 +0200

On that point: while writing my post, I dodged the question of how to call
_N by its name. I probably should have said "system variable", as in -h


-----Original Message-----
[] On Behalf Of Nick Cox
Sent: Monday, September 01, 2008 5:51 PM
Subject: st: RE: RE: Trouble with `=`_N'-1'

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


Martin Weiss

Stata does not know what to do about `_N', so it evaluates to nothing.
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
well defined and the expression evaluates to the desired value. Note
you could have put - in -2 - to begin with, and would have saved
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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