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st: RE: New command in SSC: -checkfor2-

From   "Nick Cox" <>
To   <>
Subject   st: RE: New command in SSC: -checkfor2-
Date   Mon, 19 Sep 2005 18:05:54 +0100

Note that -checkfor2- runs the user-written command -nmissing- 
which would need to be installed separately if a user had 
not previously installed that. The help file makes 
a cross-reference to this program but does not spell out 
that it is required. 

As it happens, it is not clear why -nmissing- is used at 
all, as it is only employed to pick up the number of 
missings which could, and indeed should, be done much 
more efficiently and directly with a -count-. 

Another detail that is worthy of note is that -checkfor2- 
-sort-s on each variable in turn. This is not documented, 
appears unnecessary for what the program does, and is 
indeed a misfeature as in general -checkfor2- will 
change the sort order of your data. I think it is a 
good principle that Stata commands should only change 
the sort order of your data when that is a purpose 
of the command and is also explicitly documented. 

> Thanks to Prof. Baum, a new Stata command is available from the SSC
> archives:
> -checkfor2- A Stata module to check whether a variable exists 
> or not in a
> dataset.
> Description:
> checkfor2 is a routine to check for existence of a list of 
> variables within a
> (usually big) data set.
> checkfor2 searchs through the data whether the variable 
> exists. If it does not,
> a message is issued.
> If it does, the program looks for missings structure. 
> Finally, if requested, the
> program stores the
> available variables in a macro for future use. A tolerance 
> level for missings
> could also be set.
> To install the package, type:
>    .ssc install checkfor2

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