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Editorial Team
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Asked: 2026-06-15T23:48:58+00:00

Using R, what is the best way to read a symmetric matrix from a

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Using R, what is the best way to read a symmetric matrix from a file that omits the upper triangular part. For example,

1.000
.505  1.000
.569  .422  1.000
.602  .467  .926  1.000
.621  .482  .877  .874  1.000
.603  .450  .878  .894  .937  1.000

I have tried read.table, but haven’t been successful.

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1 Answer

  1. Editorial Team

    Here’s a read.table and loopless and *apply-less solution:

    txt <- "1.000
.505  1.000
.569  .422  1.000
.602  .467  .926  1.000
.621  .482  .877  .874  1.000
.603  .450  .878  .894  .937  1.000"
 # Could use clipboard or read this from a file as well.
mat <- data.matrix( read.table(text=txt, fill=TRUE, col.names=paste("V", 1:6))  )
mat[upper.tri(mat)] <- t(mat)[upper.tri(mat)]
> mat
        V1    V2    V3    V4    V5    V6 
[1,] 1.000 0.505 0.569 0.602 0.621 0.603
[2,] 0.505 1.000 0.422 0.467 0.482 0.450
[3,] 0.569 0.422 1.000 0.926 0.877 0.878
[4,] 0.602 0.467 0.926 1.000 0.874 0.894
[5,] 0.621 0.482 0.877 0.874 1.000 0.937
[6,] 0.603 0.450 0.878 0.894 0.937 1.000
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