Translate a column index into an Excel Column Name

Question

Given a columns\' index, how can you get an Excel column name?

The problem is trickier than it sounds because it\'s not just base-26. The columns

Answer 1

The php version, thank's to this post to help me figure it out ! ^^

/**
 * Get excel column name
 * @param index : a column index we want to get the value in excel column format
 * @return (string) : excel column format
 */
function getexcelcolumnname($index) {
    //Get the quotient : if the index superior to base 26 max ?
    $quotient = $index / 26;
    if ($quotient >= 1) {
        //If yes, get top level column + the current column code
        return getexcelcolumnname($quotient-1). chr(($index % 26)+65);
    } else {
        //If no just return the current column code
        return chr(65 + $index);
    }
}

Answer 2

This JavaScript version shows that at its core it's a conversion to base 26:

function colName(x)
{
    x = (parseInt("ooooooop0", 26) + x).toString(26);
    return x.slice(x.indexOf('p') + 1).replace(/./g, function(c)
    {
        c = c.charCodeAt(0);
        return String.fromCharCode(c < 64 ? c + 17 : c - 22);
    });
}

The .toString(26) bit shows that Joel Coehoorn is wrong: it is a simple base conversion.

(Note: I have a more straight-forward implementation based on Dana's answer in production. It's less heavy, works for larger numbers although that won't affect me, but also doesn't show the mathematical principle as clearly.)

P.S. Here's the function evaluated at important points:

0 A
1 B
9 J
10 K
24 Y
25 Z
26 AA
27 AB
700 ZY
701 ZZ
702 AAA
703 AAB
18276 ZZY
18277 ZZZ
18278 AAAA
18279 AAAB
475252 ZZZY
475253 ZZZZ
475254 AAAAA
475255 AAAAB
12356628 ZZZZY
12356629 ZZZZZ
12356630 AAAAAA
12356631 AAAAAB
321272404 ZZZZZY
321272405 ZZZZZZ
321272406 AAAAAAA
321272407 AAAAAAB
8353082580 ZZZZZZY
8353082581 ZZZZZZZ
8353082582 AAAAAAAA
8353082583 AAAAAAAB

Answer 3

in python, with recursion. translated from Joey's answer. so far, it's tested to work up to GetExcelByColumn(35) = 'AI'

def GetExcelColumn(index):

    quotient = int(index / 26)

    if quotient > 0:
        return GetExcelColumn(quotient) + str(chr((index % 26) + 64))

    else:
        return str(chr(index + 64))