问在R中创建一个顺序字母列表，如excel标题中的

EN

num2let <- function(n, lets = LETTERS) {
  base <- length(lets)
  if (length(n) > 1) return(sapply(n, num2let, lets = lets))
  stopifnot(n > 0)
  out <- ""
  repeat {
    if (n > base) {
       rem <- (n-1) %% base
       n <- (n-1) %/% base
       out <- paste0(lets[rem+1], out)
    } else return( paste0(lets[n], out) )
  }
}

let2num <- function(x, lets = LETTERS) {
  base <- length(lets)
  s <- strsplit(x, "")
  sapply(s, function(x) sum((match(x, lets)) * base ^ seq(length(x) - 1, 0)))
}

lets <- num2let(1:40)
lets
## [1] "A"  "B"  "C"  "D"  "E"  "F"  "G"  "H"  "I"  "J"  "K"  "L"  "M"  "N"  "O" 
## [16] "P"  "Q"  "R"  "S"  "T"  "U"  "V"  "W"  "X"  "Y"  "Z"  "AA" "AB" "AC" "AD"
## [31] "AE" "AF" "AG" "AH" "AI" "AJ" "AK" "AL" "AM" "AN"


let2num(lets)
## [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
## [26] 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

num2let(599)
## [1] "WA"

let2num("WA")
## [1] 599