# Re: Fwd: st: Matrix transformation

 From "Susan Olivia" To statalist@hsphsun2.harvard.edu Subject Re: Fwd: st: Matrix transformation Date Fri, 03 Apr 2009 16:57:42 -0700

```Thanks heaps Glenn for the programming tips. It's doing
exactly what I after.

Susan

----- Original Message Follows -----
From: Susan Olivia <susan.olivia@gmail.com>
To: Susan Olivia <olivia@primal.ucdavis.edu>
Subject: Fwd: st: Matrix transformation
Date: Fri, 3 Apr 2009 16:40:23 -0700

> ---------- Forwarded message ----------
> From: Glenn Goldsmith <glenn.goldsmith@gmail.com>
> Date: Fri, Apr 3, 2009 at 4:08 PM
> Subject: st: Matrix transformation
> To: statalist@hsphsun2.harvard.edu
>
>
> Hi Susan,
>
> As far as I'm aware Stata/Mata don't really do sparse
> matrix storage, but you can otherwise replicate the
> behavior of sparse() with the following mata function:
>
> ********* Begin code **************
> mata:
> real matrix sparse(real matrix x)
> {
>  real matrix y
>  real scalar k
>
>  y = J(colmax(x[,1]),colmax(x[,2]),0)
>  for (k=1; k<=rows(x); k++) {
>    y[x[k,1],x[k,2]] = y[x[k,1],x[k,2]] + x[k,3]
>  }
>
>  return(y)
> }
> end
> ********* End code ****************
>
> You can then call this either from within mata:
>
>  y = sparse(x)
>
> or within stata:
>
>  mata : st_matrix("y",sparse(st_matrix("x")))
>
> (in both cases assuming that your input matrix is called x
> , and output matrix is called y).
>
> HTH,
>
> Glenn
>
>
> "Susan Olivia" <olivia@primal.ucdavis.edu> wrote:
>
> Dear all,
>
> I would like to transform a say 4272 x 3 matrix (this
> matrix basically tells us the distance between each pairs
> of observation) onto 1068 x 1068.
>
> In MATLAB, this can be transformed using the following
> command:
>
> W4NN = sparse(GIS_4NN(:,1), GIS_4NN(:,2), GIS_4NN(:,3));
>
> Is there any equivalent command like the above in STATA?
>
> Any tips on this much appreciated.
>
> Thanks,
>
> Susan
>
> *
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>
*
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```