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st: RE: Generating grouped variable list of xi'd variables via column names

From   "Maarten Buis" <>
To   <>
Subject   st: RE: Generating grouped variable list of xi'd variables via column names
Date   Fri, 13 Jul 2007 13:47:45 +0200

--- K Jensen wrote:
> I would like to generate lists of groups of variables that have been
> generated via xi from the column names of the vector e(b) after
> regression commands.
> It's probably easier to explain with an example...
>   sysuse cancer
>   stset studytime, fail(died)
>   gen randcat=1
>   replace randcat=2 if uniform()>1/3
>   replace randcat=3 if uniform()>2/3
>   xi:stcox i.drug age i.randcat
>   . matrix list e(b)
>   e(b)[1,5]
>          _Idrug_2     _Idrug_3          age  _Irandcat_2  _Irandcat_3
>   y1   -1.7300519   -3.2313217    .12791436   -.93457115   -.77850524
> I would like to take the column names from e(b) to generate a varlist
> of the xi-generated variable groups, something like:
>_Idrug* _Irand*

With the -unab- command you can get a list of all variable names 
starting with _I, with the -indeplist- command (downloadable from ssc) 
you can get a list of all independent variables in your model, and 
with the list extended macro function you combine these two list to 
create a list of all _I variables that are in your model. See the 
example below:

*-------------- begin example -----------
sysuse cancer, clear
stset studytime, fail(died)
gen randcat= ceil(3*uniform())
xi:stcox i.drug age i.randcat

indeplist, local
di "`X'"
unab all_I : _I*
local model_I : list all_I & X
di "`model_I'"
*-------------- end example -------------
(For more on how to use examples I sent to the Statalist, see )

Hope this helps,

Ps. Notice that I created the variable randcat differently. You
created it by calling the function uniform() twice. That way 
-uniform()>1/3- and -uniform()>2/3- can both be true since they
refer to different random numbers. More on this in Stata Tip 48
which will appear in the next Stata Journal. A pre-publication
draft is downloadable from my website.

Maarten L. Buis
Department of Social Research Methodology 
Vrije Universiteit Amsterdam 
Boelelaan 1081 
1081 HV Amsterdam 
The Netherlands

visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434 

+31 20 5986715

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