Convert Matrix into Symmetric in R

• require(Matrix):

forceSymmetric(dat, uplo="U"))

• Assign the lower triangular part  to the upper triangular part:

dat[upper.tri(dat)] <- t(dat)[lower.tri(dat)]

• micEcon package:

symMatrix(dat[upper.tri(dat, TRUE)], nrow=nrow(dat), byrow=TRUE)