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st: RE: access subsets of a matrix


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: access subsets of a matrix
Date   Wed, 27 Apr 2005 22:30:50 +0100

In the current version of Stata, there 
is a Mata solution for this. 

In Stata 8, which I guess you 
are using, I don't think there is 
an exact equivalent to the Matlab construct. 

You would need a loop, something like this: 

forval i = 1/`=rowsof(lambda)' { 
	<calculate whatever> 
	if z[`i'] == 0 lambda[`i'] = -normden(<whatever>) 
} 



Nick 
n.j.cox@durham.ac.uk 

> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of Jens
> Hainmueller
> Sent: 27 April 2005 22:08
> To: statalist@hsphsun2.harvard.edu
> Subject: st: access subsets of a matrix
> 
> 
> Hi,
> 
> I am new to Stata programming so I have a problem to 
> translate the following
> line of mathlab code into Stata code.
> 
> lambda(z==0) = - normpdf(X(z==0,:)*gamma)
> 
> Here lambda is an (nx1) matrix, X is (nxk), gamma is (kx1), z 
> is (nx1), and
> for example X(z==0) denotes subset of the matrix X for which 
> (z==1), i.e.
> the condition in parenthesis holds true.
> 
> In Stata, how can I access this subset of my X matrix? It should be
> something like:
> 
> matrix lambda = -normde(X[if z==1]*gamma)
> 
> but I can't Stata to access the matrix subsets as I need it. 
> Thanks for your
> help.
> 
> Best,
> Jens
> 
> 
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