R/contr.simplex.R

In skpr: Design of Experiments Suite: Generate and Evaluate Optimal Designs

#'@title Orthonormal Contrast Generator
#'
#'@description Generates orthonormal (orthogonal and normalized) contrasts. Each row is the vertex of an N-dimensional simplex. The only exception are contrasts for the 2-level case, which return 1 and -1.
#'
#'@param n The number of levels in the catagorical variable. If this is a factor or character vector, `n` will be `length(n)`
#'@param size Default `1`. The length of the simplex vector.
#'@return A matrix of Orthonormal contrasts.
#'@export
#'@examples contr.simplex(4)
contr.simplex = function(n, size=NULL) {
  if(is.factor(n) || is.character(n)) {
    n = length(n)
  }
  results = matrix(nrow = n - 1, ncol = n)
  if (n == 1) {
    stop("skpr: Too few dimensions for contrast generation")
  }
  if (n == 2) {
    results[, 1] = 1
    results[, 2] = -1
    return(t(results))
  }
  if (is.null(size)) {
    size = sqrt(n - 1)
  }
  results[1, ] = c(size, rep(-size / (n - 1), n - 1))
  results[-1, 1] = 0
  for (i in 2:(n - 1)) {
    results[i:(n - 1), i] = 0
    results[i, i] = sqrt(size ^ 2 - sum(results[1:(i - 1), i] ^ 2))
    results[i, (i + 1):n] = -results[i, i] / length( (i + 1):n)
  }
  return(t(results))
}