问题
I have a lower triangular of a matrix that I'm trying to convert to a dissim matrix and thus it needs to be symmetric.
print(rdf)
X0 X1 X2 X3 X4
0 0.0000000 NA NA NA NA
1 0.5340909 0.0000000 NA NA NA
2 0.5340909 0.0000000 0.0000000 NA NA
3 0.3200000 0.5227273 0.5227273 0.0000000 NA
4 0.6263736 0.4945055 0.4945055 0.5384615 0
library(gdata)
upperTriangle(rdf) <- lowerTriangle(rdf)
isSymmetric(rdf)
X0 X1 X2 X3 X4
0 0.0000000 0.5340909 0.5340909 0.6263736 0.4945055
1 0.5340909 0.0000000 0.3200000 0.0000000 0.5227273
2 0.5340909 0.0000000 0.0000000 0.5227273 0.4945055
3 0.3200000 0.5227273 0.5227273 0.0000000 0.5384615
4 0.6263736 0.4945055 0.4945055 0.5384615 0.0000000
[1] FALSE
What is going on? Note, I don't need to use gdata
回答1:
You need to make sure that the elements you're copying are ordered correctly:
m <- matrix(NA,4,4)
m[lower.tri(m,diag=TRUE)] <- 1:10
[,1] [,2] [,3] [,4]
[1,] 1 NA NA NA
[2,] 2 5 NA NA
[3,] 3 6 8 NA
[4,] 4 7 9 10
makeSymm <- function(m) {
m[upper.tri(m)] <- t(m)[upper.tri(m)]
return(m)
}
makeSymm(m)
Or you can use the built-in
Matrix::forceSymmetric(m,uplo="L")
来源：https://stackoverflow.com/questions/33026183/r-make-symmetric-matrix-from-lower-diagonal