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st: RE: RE: Filling upper triangle of a symetric matrix


From   "Ronnie Babigumira" <ronnie.babigumira@ios.nlh.no>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: RE: Filling upper triangle of a symetric matrix
Date   Wed, 26 Mar 2003 17:31:16 +0100

Thanks Nick
Works like a charm (can it be generalized for similar problems or is it not
worth the extra bit)

Ronnie

Ronnie wrote

> (Stata 8, win 2K) I have a correlation matrix in excel (I
> dont have the data
> from which it was obtained) and I would like to perform
> factor analysis on
> this matrix. This is possible if by using corr2data, I generate the
> underlying data and then I can perform the factor analysis.
>
> Here is my correlation matrix
> Corr Matrix
> 1
> 0.439	1
> 0.41	0.351	1
> 0.288	0.354	0.164	1
> 0.329	0.32	0.19	0.595	1
> 0.248	0.329	0.181	0.47	0.464	1
>
> If I try to read this in stata (using insheet), I get 6 new
> variables with
> missing cases
>
>   +---------------------------------------+
>   |   v1     v2     v3     v4     v5   v6 |
>   |---------------------------------------|
>   |    1      .      .      .      .    . |
>   | .439      1      .      .      .    . |
>   |  .41   .351      1      .      .    . |
>   | .288   .354   .164      1      .    . |
>   | .329    .32    .19   .595      1    . |
>   |---------------------------------------|
>   | .248   .329   .181    .47   .464    1 |
>   +---------------------------------------+
> I then convert this into a matrix using mkmat and I get
>
> a[6,6]
>           1          .          .          .          .          .
>   .43900001          1          .          .          .          .
>         .41  .35100001          1          .          .          .
>   .28799999       .354       .164          1          .          .
>        .329  .31999999        .19  .59500003          1          .
>        .248       .329  .18099999        .47  .46399999          1
>
> Question. How can I tell stata that this is a symetric
> matrix and fill in
> the missing ijs with the corresponding ji values? (or, how
> can I do this in
> excel)

forval i = 1/6 {
	forval j = 1 / 6 {
		if a[`i',`j'] == . matrix a[`i',`j']  = a[`j',`i']
	}
}

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