Convert a spreadsheet cell reference (A1) to row-column (1, 1) format (overengineered draft)

cr2rc.R

cr2rc <- function(cell_ref) {

  ref_split <-
    strsplit(cell_ref, "(?<=[[:alpha:]])(?=[[:digit:]])", perl = TRUE)[[1]]

  if (length(ref_split) != 2) {
    stop(
      "You must supply a cell reference of 1 to 3 letters (the column reference) ",
      "followed by a number (the row reference), like 'A1' or 'ABC100'.",
      call. = FALSE
    )
  }

  if (
    !inherits(ref_split[1], "character") |
    !inherits(type.convert(x = ref_split[2], as.is = TRUE), "integer")
  ) {
    stop(
      "The first part (the column reference) must be a string ",
      "and the second must (the row reference) be an integer",
      call. = FALSE
    )
  }

  row_int <- as.integer(ref_split[2])

  if (!inherits(row_int, "integer") & col_num > 0) {
    stop("Row reference must be a positive integer", call. = FALSE)
  }

  col_lets <- toupper(strsplit(ref_split[1], "")[[1]])
  col_vals <- unname(sapply(col_lets, function(let) which(LETTERS == let)))

  if (length(col_vals) > 3) {
    stop("The column reference must be three letters or fewer.", call. = FALSE)
  }

  col_num <- col_vals[1]

  if (length(col_vals) == 2) {
    col_num <- (col_vals[1] * 26) + col_vals[2]
  }

  if (length(col_vals) == 3) {
    col_num <- (col_vals[1] * 26 * 26) + (col_vals[2] * 26) + col_vals[3]
  }

  col_int <- as.integer(col_num)

  if (!inherits(col_int, "integer") & col_num > 0) {
    stop("Column reference must be a positive integer", call. = FALSE)
  }

  c(col = col_int, row = row_int)

}