st: Convert Geoda .GWT to stata format

[rraciborski@stata.com]

Adiwan Fahlan <adiwan_f@yahoo.com> asks

> Could anyone help me to convert from Geoda's .GWT spatial weight matrix to a
> Stata file?

Below I describe the steps needed to accomplish this task in Stata.

Before we begin, if Adiwan does not have the user-written -spmat- command,
Adiwan should intall it by typing in Stata

  . ssc install sppack

-sppack- contains three Stata commands, -spmat-, -spreg-, and -spivreg-.
-spmat- is used for creating and managing spatial-weighting matrix objects
(spmat objects) while -spreg- and -spivreg- are used to fit
spatial-autoregressive models.

Assume Adiwan's file is named 'myfile.GWT'.  First, we use -spmat import- to
read the GeoDa file

  . spmat import myobj using myfile.GWT, geoda

-spmat import- created an spmat object named 'myobj' that contains the
spatial-weighting matrix constructed from the information contained in the
GeoDa file.

If Adiwan wants to use this spatial-weighting matrix to fit a
spatial-autoregressive model, there is no need to save the matrix to a Stata
file.  Instead Adiwan can use the spmat object 'myobj' with -spreg- or
-spivreg-.

If Adiwan still wants to store the spatial-weighting matrix to a Stata file, the
next step is to extract the spatial-weighting matrix from the spmat object and
store it as a regular Mata matrix, I call it 'W'

  . spmat getmatrix myobj W

The last step is to store that matrix as a Stata dataset.  In the example below,
the variables in the dataset will be named x1, x2, x3, ...

  . getmata (x*)=W

Finally, since spatial-weighting matrices consume a lot of memory, I would make
sure to clear 'W' and 'myobj' from memory

  . spmat drop myobj
  . mata mata drop W

--Rafal
rraciborski@stata.com
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