I'm looking for a nice way to have a variable alpha that would increment as follow: when x=0 -> alpha = "A"; x=1 -> alpha = "B"; ... x=25 -> alpha = "Z"; x=26 -> alpha = "AA"; x=27 -> alpha = "AB"

I'm looking for a nice way to have a variable alpha that would increment as follow: when x=0 -> alpha = "A"; x=1 -> alpha = "B"; ... x=25 -> alpha = "Z"; x=26 -> alpha = "AA"; x=27 -> alpha = "AB"

• javascript

Share Improve this question Follow edited Jan 13, 2017 at 9:48 Nate asked Jan 12, 2017 at 11:08 NateNate 7,8862323 gold badges7676 silver badges129129 bronze badges

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4 Answers 4

Sorted by: Reset to default 6

You could use toString with base 36 for converting to the wanted letters.

function convert(n) {
    var result = '';
    do {
        result = (n % 26 + 10).toString(36) + result;
        n = Math.floor(n / 26) - 1;
    } while (n >= 0)
    return result.toUpperCase();
}

//           A  B   Z  AA  AB   CZ   DXH
console.log([0, 1, 25, 26, 27, 103, 3335].map(convert));

.as-console-wrapper { max-height: 100% !important; top: 0; }

EDITED

OK sorry I just didn't understand your need at first. Here is a working code.

Try this:

var x = 807;
var alpha = '';
var alphabetLength = 26;


var y = x.toString(alphabetLength);
chars = y.split('');
for (var i=0; i < chars.length; i++ ) {
	var charFactor = 65;
	var curChar = chars[i];
	if (isNaN(curChar)) {
	
		alpha += String.fromCharCode(curChar.toUpperCase().charCodeAt() + 10);
	} else {
		if ( i < chars.length-1) {
			charFactor--;
		}
		alpha += String.fromCharCode(parseInt(curChar) + charFactor);
	}
}

console.log(alpha)

Use String.fromCharCode method and generate string using char code.

// initialize as empty string
var alpha = '';
// iterate upto value is reaching -1 since index starts from 0
while (x > -1) {
  // get charactor by finding remainder 
  // and concatenate it with alpha
  alpha = String.fromCharCode(65 + x % 26) + alpha;
  // update value of variable x 
  // decrement by 1 since index starts from 0
  x = Math.floor(x / 26) - 1;
}

[1, 28, 25, 26, 27, 3335, 12, 10, 3, 6, 0].forEach(function(x) {
  var alpha = '';
  while (x > -1) {
    alpha = String.fromCharCode(65 + x % 26) + alpha;
    x = Math.floor(x / 26) - 1;
  }
  console.log(alpha);
});

I ended up with a one liner for this:

(alpha).toString(26).split('').map((b26) => (parseInt(b26,26) + 10).toString(36)).join('').toUpperCase()

The basic idea is to convert your number into base 26, which means 0-9a-p, and then add 10 so that the output range is a-z.

Here's a quick test showing that it works for the first 100 numbers.

for (let i = 0; i < 100; i++) {
  console.log(i, (i).toString(26).split('').map((b26) => (parseInt(b26,26) + 10).toString(36)).join('').toUpperCase())    
}