Number to Excel column name conversion - php

Question

In Excel, column names are characters from A to Z, if there are more columns needed, it continues with AA, AB ...
I want to write a function, that converts integers to those excel column names.
0 .... A
25 ... Z
26 ... AA
702 ... AAA
.
.
.
The solution I came up with is working up to AZ, but I want it to work further.
function indexToXlxsColumn($index, $prefix="")
{
if($index < 26)
{
return $prefix.chr($index+65);
}else{
return indexToXlxsColumn($index % 26, "A");
}
}
How to adapt this function to work for every index without producing spaghetti code?

Answer 1

Here is the probleme
return indexToXlxsColumn($index % 26, "A");
You away set the next floor prefix to A , what happends when u have
input = 53 , the resultat should be "BB"
Code on paper
function indexToXlxsColumn($index, $prefix="")
{
if($index < 26) // 53 isnt less then 26
// second loop , 1 is less then 26
{
return $prefix.chr($index+65);
// $prefix = A
// chr($index+65) = B
// return "A"."B" ;
}else{
return indexToXlxsColumn($index % 26, "A");
// indexToXlxsColumn(53 % 26, "A") -> (1, "A")
}
}
---UPDATE---
Follow the ask here is the answer
function indexToXlxsColumn($index, $suffix ="")
{
if($index < 26){
return chr($index+65).$suffix ;
}
return indexToXlxsColumn(($index - $index%26)/26-1, chr($index%26+65).$suffix );
}

Answer 2

One of the implementations:
function indexToXlxsColumn($index)
{
$name = '';
while($index > 0) {
$mod = ($index - 1) % 26;
$name = chr(65 + $mod).$name;
$index = (int)(($index - $mod) / 26);
}
return $name;
}
// echo indexToXlxsColumn(26); // Z
echo indexToXlxsColumn(33); // AG
// echo indexToXlxsColumn(800); // ADT

Answer 3

I would do it a little differently. It bothered me to work with chr(). So I once stored the alphabet in a string and iterated over it until the index was successfully resolved.
max "zz"
<?php
function getIn($i) {
$str = 'abcdefghijklmnopqrstuvwxyz';
$r = (int) floor($i / 26) ;
$c = $i % 26;
return ($r) < 1 ? $str[$c] : $str[$r-1] . $str[$c];
}
echo getIn(52); // output: "ba"
Update with max "zzz"
function getIn($i) {
$str = 'abcdefghijklmnopqrstuvwxyz';
$r = (int) floor($i / 26);
$rr = $r >= 27 ? $r - 27 : null;
$c = $i % 26;
if ( $rr !== null) {
return $str[$c] : $str[$r-1] . $str[$c];
}
return ($r) < 1 ? $str[$c] : $str[$r-1] . $str[$c];
}
echo getIn(800); // ddu
echo getIn(1377); // zzz

Answer 4

PLACEHOLDER parts of the code return squiffy values! Needs review before using in the wild!!
In case anyone wants a utility function that does this, here's a python implementation:
n2AA performs the calculation from numeric to "AA" format.
def n2AA(n):
n=n-1
alphabet=["_"] + [chr(c+65) for c in range(0,26)]
w=len(alphabet)-1
accum=[]
for e in range(5,-1,-1):
expon=w**e
s=(n//expon)
r=n%expon
n=n-(s*expon)
if e>0:
accum.append(alphabet[s])
else:
accum.append(alphabet[s+1])
return "".join([a for a in accum if a != "_"])
And AA2n performs the inverse function, starting with "AA" format and returning the column number (starting at 1).
def AA2n(AA):
alphabet=["_"] + [chr(c+65) for c in range(0,26)]
w=len(alphabet)-1
accum=[]
for c in range(0,len(AA)):
expon=w**(len(AA)-1-c)
accum.append((alphabet.index(AA[c]))*expon)
return sum(accum)