# Implement numbering scheme like A,B,C… AA,AB,… AAA…, similar to converting a number to radix26

I want to implement numbering scheme like Microsoft Word uses for numbering. first one gets = A,next is B, next is C, .... then AA, then AB,....and so on. as shown below

 A
B
C
.
.
AA
AB
AC
.
.
AAA
AAB
....


'=>' here means converted to.

some examples:

1 => A
26 => Z
27 => AA
52 => AZ
53 => BA


and heres the code for it:

   var convertToNumberingScheme = function(n){
var x = n-1,
r26 = x.toString(26),
baseCharCode = "A".charCodeAt(0);

var arr = r26.split(''),
len = arr.length;

var newArr =arr.map(function(val,i){
val = parseInt(val,26);

if( (i === 0) && ( len > 1)){
val = val-1;
}

return String.fromCharCode(baseCharCode + val);
});
return newArr.join('');
}


It seems to work fine, but any ideas if there are some potential bugs or ways to optimize this.

• If you're using HTML then just place ul or ol. – Larry Battle Oct 2 '12 at 21:30
• @LarryBattle Thanks. But it is a custom canvas app, can't use ul,li but good pointer nonetheless . – sbr Oct 2 '12 at 21:34

The function in the question converts to base 26, then splits the resulting string, and converts each digit back to decimal - and then to a letter. That seems roundabout.

Here's a simpler one:

function convertToNumberingScheme(number) {
var baseChar = ("A").charCodeAt(0),
letters  = "";

do {
number -= 1;
letters = String.fromCharCode(baseChar + (number % 26)) + letters;
number = (number / 26) >> 0; // quick floor
} while(number > 0);

return letters;
}


This function basically does a repeated "divmod" of the input number; getting the modulus 26 and the quotient (floor of n divided by 26). The modulus is converted to a A-Z character that's prepended to the output string, and the quotient is used as the input for the next iteration of the loop.