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st: Re: Extracting specific elements from a matrix


From   Dani Tilley <tilleydani@yahoo.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Re: Extracting specific elements from a matrix
Date   Mon, 5 Jul 2010 14:23:53 -0700 (PDT)

Awesome. Thanks so much for the help.



----- Original Message ----

<>


Vectors are not really part of Stata parlance, I am afraid, which may 
well
be a shock for those who previously used other products.

When you say -generate-, you create a new column of data. If you want 
only
the first ten rows to be filled with data, as for the "y" variable in 
the
example, you can do that, but the rest (11 to _N) must contain 
something,
they cannot just be blank, as in some spreadsheet software products.

***
clear*
set obs 15
gen byte x=_n
gen byte y=_n in 1/10
l
***



You may also want to look at the -el()- function, btw.


HTH
Martin
From: Dani Tilley <tilleydani@yahoo.com>
To: statalist@hsphsun2.harvard.edu
Sent: Mon, July 5, 2010 5:10:15 PM
Subject: Re: Extracting specific elements from a matrix

Much appreciated Martin. Incidentally, how do you go about creating an empty vector in Stata? I noticed that -generate- creates a new variable of length N,but what if I want a variable of length 10? I tried macro and local but they appear to hold strings rather than floats. 



----- Original Message ----

<>

Either talk to the coeff as "_b" (-help _variables-) or define a 
-matrix-
and extract from it:

***********
sysuse auto, clear
reg price weight length rep78

di _b[weight]

mat A=e(b)
di A[1,1]
***********


HTH
Martin
From: Dani Tilley <tilleydani@yahoo.com>
To: statalist@hsphsun2.harvard.edu
Sent: Mon, July 5, 2010 4:36:25 PM
Subject: Extracting specific elements from a matrix

Hi,

I need to extract the first element of a matrix of coefficients and store it on a variable, and repeat the process i times. I can set up the for loop and do the storing, but I don't know how to access element [i,j] of a matrix A.

In particular, my matrix is e(b), the vector of coefficients from a regression with k explanatory variables. I tried -e(b)[1,1]- but that didn't take me far.

Any help is appreciated.

Thanks,
DF Tilley


      
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