excelCols.R

# taken from the fifer package
# https://github.com/dustinfife/fifer

excelCols <- function (n) 
{
  vec1 = LETTERS
  if (n <= 26) {
    res = vec1[seq_len(n)]
  }
  else if (n > 26 & n <= 702) {
    res = c(vec1, apply(expand.grid(vec1, vec1)[, 2:1], 
      1, paste, collapse = ""))[1:n]
  }
  else if (n > 702 & n <= 18278) {
    res = c(vec1, apply(expand.grid(vec1, vec1)[, 2:1], 
      1, paste, collapse = ""), apply(expand.grid(vec1, 
      vec1, vec1)[, 3:1], 1, paste, collapse = ""))[1:n]
  }
  else {
    res = NA
  }
  res
}