Algorithm to get the excel-like column name of a number

Question

I\'m working on a script that generate some Excel documents and I need to convert a number into its column name equivalent. For example:

1 => A
2 => B
         


        

Answer 1

Late answer, but here's what I did (for 1==A indexed):

function num_to_letters($num, $uppercase = true) {
    $letters = '';
    while ($num > 0) {
        $code = ($num % 26 == 0) ? 26 : $num % 26;
        $letters .= chr($code + 64);
        $num = ($num - $code) / 26;
    }
    return ($uppercase) ? strtoupper(strrev($letters)) : strrev($letters);
}

Then if you want to convert the other way:

function letters_to_num($letters) {
    $num = 0;
    $arr = array_reverse(str_split($letters));

    for ($i = 0; $i < count($arr); $i++) {
        $num += (ord(strtolower($arr[$i])) - 96) * (pow(26,$i));
    }
    return $num;
}

Answer 2

I'd never use this in production because it's not readable, but for fun... Only does up to ZZ.

<?php
    $col = 55;
    print (($n = (int)(($col - 1) / 26)) ? chr($n + 64) : '') . chr((($col - 1) % 26) + 65);
?>

Answer 3

<?php
function numberToColumnName($number){
    $abc = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    $abc_len = strlen($abc);

    $result = "";
    $tmp = $number;

    while($number > $abc_len) {
        $remainder = $number % $abc_len;
        $result = $abc[$remainder-1].$result;
        $number = floor($number / $abc_len);
    }
    return $abc[$number-1].$result;
}

echo numberToColumnName(1)."\n";
echo numberToColumnName(25)."\n";
echo numberToColumnName(26)."\n";
echo numberToColumnName(27)."\n";
echo numberToColumnName(28)."\n";
echo numberToColumnName(14558)."\n";
?>

Answer 4

This will do to conversion (assuming integer arithmetic), but I agree with the other posters; just use base_convert

function numberToColumnName($number)
{
    $abc = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    $len = strlen($abc);

    $result = "";
    while ($number > 0) {
       $index  = $number % $len;
       $result = $abc[$index] . $result;
       $number = floor($number / $len);
    }

    return $result;
}

Answer 5

Here's a nice simple recursive function (Based on zero indexed numbers, meaning 0 == A, 1 == B, etc)...

function getNameFromNumber($num) {
    $numeric = $num % 26;
    $letter = chr(65 + $numeric);
    $num2 = intval($num / 26);
    if ($num2 > 0) {
        return getNameFromNumber($num2 - 1) . $letter;
    } else {
        return $letter;
    }
}

And if you want it one indexed (1 == A, etc):

function getNameFromNumber($num) {
    $numeric = ($num - 1) % 26;
    $letter = chr(65 + $numeric);
    $num2 = intval(($num - 1) / 26);
    if ($num2 > 0) {
        return getNameFromNumber($num2) . $letter;
    } else {
        return $letter;
    }
}

Tested with numbers from 0 to 10000...

Answer 6

Using PhpSpreadsheet (PHPExcel is deprecated)

// result = 'A'
\PhpOffice\PhpSpreadsheet\Cell\Coordinate::stringFromColumnIndex(1);

Note index 0 results in 'Z'

https://phpspreadsheet.readthedocs.io/en/develop/

---

The correct answer (if you use PHPExcel Library) is:

// result = 'A'
$columnLetter = PHPExcel_Cell::stringFromColumnIndex(0); // ZERO-based! 

and backwards:

// result = 1
$colIndex = PHPExcel_Cell::columnIndexFromString('A');