R/vec2symMat.R

In metaSEM: Meta-Analysis using Structural Equation Modeling

vec2symMat <- function (x, diag=TRUE, byrow=FALSE) {
  m <- length(x)
  d <- if (diag) 1 else -1
  n <- floor((sqrt(1 + 8*m) - d)/2)
  if (m != n*(n + d)/2) 
    stop("Cannot make a square matrix as the length of \"x\" is incorrect.")
  mat <- Diag(n)

  ## Row major
  if (byrow) {
    mat[upper.tri(mat, diag=diag)] <- x
    index <- lower.tri(mat)
    mat[index] <- t(mat)[index]  
  } else {
  ## Column major: default behavior
    mat[lower.tri(mat, diag=diag)] <- x
    # Just mirroring the matrix, exclude the diagonals
    ## mat[upper.tri(mat, diag=FALSE)] <- mat[lower.tri(mat, diag=FALSE)]
    ## Corrected a bug
    index <- upper.tri(mat)
    mat[index] <- t(mat)[index]  
  }
  mat
}