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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 13:21:07 +0100

Your understanding is not correct. 

In your example of st_view()-, -touse- contains the name of one
variable. This is explained in the help. 

Nor does -marksample- produce a list of variable names. It produces a
single variable containing 1s or 0s as appropriate. As already explained
in my previous message, it marks observations. 

I continue to think your strategy here ill-advised. You would need to
write a special Mata program or think up special Stata code for almost
every row-wise task you envisage. 

[email protected] 

Ashim Kapoor

Hello Nick,

Thank  you for your time. Also thank you for your note on sortrows.
Currently I am working on making " sortkeyrows" an ado file which will
sort using a key. I will email the ado file to the list once I am
done. I came across marksample while examining the code for sortrows.

Let me rephrase my question.

In the ado file for sortrows. we say " marksample touse".
Later on we say st_view(X,., tokens(varlist), touse)

Now if I understand st_view correctly touse should be a string of
variable names which should be non zero for selection of values. But
marksample is NOT producing is list of variable names.

Where am I wrong?

On 9/11/08, Nick Cox <[email protected]> wrote:
> -marksample- is not part of Mata. It is a Stata command.
> It marks observations, not variables.
> It produces a new temporary variable, not a matrix.
> It is possible to use -marksample- independently of -syntax-:
> . sysuse auto
> (1978 Automobile Data)
> . local if "2 == 2"
> . marksample touse, novarlist
> . su `touse'
>    Variable |       Obs        Mean    Std. Dev.       Min        Max
> -------------+--------------------------------------------------------
>    __000000 |        74           1           0          1          1
> However, it is usual to use -marksample- after -syntax-, or after a
> of commands that produced similar results. I can't think up a
> kind of situation in which -marksample- is the command of choice.
> Nick
> [email protected]
> Ashim Kapoor
> I am trying to learn MATA. I have a query. What is marksample ? Does
> it  return a matrix  with 0's in place of variables which are NOT
> marked. Is it ONLY used after syntax ?
> I did not find the help very useful. Can someone please shed some
> light on this ?

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