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RE: st: RE: marksample

From   "Nick Cox" <[email protected]>
To   <[email protected]>
Subject   RE: st: RE: marksample
Date   Thu, 11 Sep 2008 15:34:28 +0100

This is not quite correct. There is a difference between -mark- and
-marksample-. I believe that Maarten meant to type -marksample-. 

-marksample- is, primarily, for use after -syntax-, as already

-mark- implements the same idea but has as major use marking samples
during interactive work. 

[email protected] 

Maarten buis

--- Ashim Kapoor <[email protected]> wrote:
> I am reading mark from the programming manual. I get the idea of
> st_views. I do not understand what the idea behind mark is. Why is
> this variable named in a funny way like __0000 ? Is this 0 / 1 in
> each row depending on some criteria ? What is that criteria?

Often you don't want your program to apply to all observations in your
data, e.g. you want to ignore rows where at least one of the variable
you use in your data contains missing values, or want to allow users to
restrict their analysis to females only. 

-mark- is a convenience command: it collects after -syntax- the
relavant variables and marks out (gives them value 0 on the variable
`touse') observations with missing values on those. It also looks at 
-in- and -if- restrictions.

It is called __000 (though you should never refer to it that way)
because it is a temporary variable: it is removed once your program is
finished. The reason why you should never refer to it that way is that
it could also be called __001 or something else (depending on whether
you have defined other temporary variables before that). You should
refer to it as `touse'.

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