[R] Symmetric matrix

Dimitris Rizopoulos d.rizopoulos at erasmusmc.nl
Sun Sep 21 19:58:44 CEST 2008

try the following

a <- matrix(rnorm(36), 6)
ind <- lower.tri(a)
a[ind] <- t(a)[ind]

I hope it helps.


Megh Dal wrote:
> I have following matrix :
> a = matrix(rnorm(36), 6)
> Now I want to replace the lower-triangular elements with it's upper-triangular elements. That is I want to make a symmetric matrix from a. I have tried with lower.tri() and upper.tri() function, but got desired result. Can anyone please tell me how to do that?
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Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus Medical Center

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