Excel column index translator with R

num.to.LETTERS.R

#Translate integer into Excel column index, such as:
# 1-26 -> A-Z
#27-52 -> AA-AZ
#53-78 -> BA-BZ
#...

num.to.LETTERS<-function(num,letter=""){
  if(num<=0){
    return(NA)
  }else if(num/26<=1){
    return(paste0(LETTERS[num],letter))
  }else{
    letter<-paste0(LETTERS[ifelse(num%%26==0,26,num%%26)],letter)
    return( num.to.LETTERS(ifelse(num%%26==0,floor(num/26-1),floor(num/26)),letter) )
  }
}

#Non-recursive
num.to.LETTERS2<-function(num){
  a<-vector()
  i=1
  rusult<-""
  while(num>0){
    n = num %% 26
    num = floor(num/26)
    if(n != 0){
      a[i]<-LETTERS[n]
    }else{
      a[i]<-LETTERS[26]
      num=num-1
    }
    i=i+1
  }
  for(i in length(a):1) rusult<-paste0(rusult,a[i]);
  return(rusult)
}