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Re: st: Allocating values from a matrix to a new variable in Stata


From   Nick Winter <nw53@cornell.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Allocating values from a matrix to a new variable in Stata
Date   Tue, 03 May 2005 13:48:55 -0400

Assuming you have the distance matrix in a Stata matrix called "D", then this should do it:

. generate distance = D[x,y]

(I am assuming that the diagonal of the distance matrix contains zeros, so there is no need to deal with x==y as a separate step.

If you have missing values for either x and/or y, you might need to modify:

. generate distance = D[x,y] if !missing(x) & !missing(y)

--Nick WInter


At 01:41 PM 5/3/2005 -0400, you wrote:

Hi,

I'm using Intercooled Stata 8, and am not an experienced user.
It will be great if someone can help me out with this.

I have a dataset where I have about 18,000 records each having a value for X
and another for Y that ranges from 1 to 32.
I have another 32*32 matrix that gives the distances between all X and Y
pairs.

Whenever a record has X=Y, I want to introduce a new variable distance =
zero.
Otherwise, I want to assign distance = the appropriate distance value for
(X,Y) from this matrix I have.

For example, if X=1 and Y=1, distance = 0.
If X=1 and Y=2, distance = 25 (value obtained from the distance matrix)
If X=2 and Y=1, distance = 25 (same as above)
If X =1 and Y=3, distance = 15 ...... And so on.

Can someone please suggest the most efficient way to do this in Stata?

Many thanks,
Anjali

------------------------------
Anjali Mahendra
Doctoral student
Department of Urban Studies and Planning
Massachusetts Institute of Technology
------------------------------

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