Re: st: funny behaviour of _N

[Philip Ryan <philip.ryan@adelaide.edu.au>]

Ashim

Funny perhaps, but logical to Stata.

In code fragment 2. below you are using the -in- qualifier.  -help 
in- explicitly states that -in- is followed by a range and gives 
allowable syntax for that range.
_N is not allowable syntax. Essentially it is not a number; it is 
what Stata calls a system variable. But its content as a number can 
be exposed by evaluation "on the fly".  Try:

replace a=b in `=_N'

In code fragment 1. below you have forced the evaluation of the 
*expression* _N by using the "=".  The number represented by _N now 
resides in local macro num.  When num is subsequently expanded it 
presents to -in- as a syntactically correct range.

Probably about now, or shortly thereafter, you should read the User's 
Guide and at least selected parts of the Data Management volume of 
the documentation.  It will repay the effort.

Phil



 At 03:53 PM 28/08/2008, you wrote:

> Hello everyone,
>
> Please compare the following 2 code snippets : -
>
> 1.
>
> local num=_N
> replace a=b in `num'
>
> 2.
>
> replace a=b in _N
>
> Surprisingly only the 1st one works ! Could some one tell me why ?
>
> Thank you,
> Ashim
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