Atypical letter and number incrementation - php

Question

I'm working on something which requires unique ID numbers which are in the format of:
[A-Z][A-Z0-9][A-Z0-9][A-Z0-9][A-Z0-9][A-Z0-9]
And increment as:
AAAAAA, AAAAAB, ... AAAAAZ, AAAAA0, AAAAA1, .. AAAAA9, AAAABA, AAAABB
I know I can increment letters in PHP, but how would I do letters and numbers in such a way?
Special note, baseconvert isn't an option, because it must always be exactly 6 characters and fit the noted format incrementally. Further, baseconvert starts at 0, not A, so if I do start at "621937810" (AAAAAA) the next jump will be after AAAAAZ and on to AAAAB0. It seemed like the quickest solution, but it doesn't work.

Answer 1

you could try base_convert from 36 to 10, increment then 10 to 36. I didn't have any trouble with the larger numbers like ZZZZZW+1, however as it says in the php manual, there could be problems with larger numbers due to float/double precision.
<?php
echo "<pre>";
//orig string
$test = 'ZZZZZW';
//convert from base36 to number.
$test = base_convert($test, 36, 10);
var_dump($test);
//increment
$test++;
var_dump($test);
//convert back (and upper case)
$test = strtoupper(base_convert($test, 10, 36));
var_dump($test);
?>
outputs:
string(6) "ZZZZZW"
string(10) "2176782332"
float(2176782333)
string(6) "ZZZZZX"
example can be see here
Other than that, you can do some custom increment or even check out the base_convert comments in the php manual on converting some larger bases and values.
Edit after clarification:
Taken from the php comments page:
<?php
function intToAlphaBaseN($n,$baseArray) {
$l=count($baseArray);
$s = '';
for ($i = 1; $n >= 0 && $i < 10; $i++) {
$s = $baseArray[($n % pow($l, $i) / pow($l, $i - 1))].$s;
$n -= pow($l, $i);
}
return $s;
}
$base=array_merge(range('A','Z'), range(0,9));
$zero = $base[0];
//an integer number
$r=rand(0, 999999);
echo "$r converts to :".str_pad(intToAlphaBaseN($r,$base), 6, $zero, STR_PAD_LEFT)."\n";
//an integer number
$r++;
echo "$r converts to :".str_pad(intToAlphaBaseN($r,$base), 6, $zero, STR_PAD_LEFT)."\n";
//an integer number
$r++;
echo "$r converts to :".str_pad(intToAlphaBaseN($r,$base), 6, $zero, STR_PAD_LEFT)."\n";
?>
working example
As for incrementing from the string ID, I would suggest either saving the integer value, increment that and convert or write a similar function to convert to integer, increment, convert back. The former probably being easier.
And as far as forcing the same 6 character format, the only time this should be a problem is when you pass the Z99999 which according to your format, is the max.

Answer 2

You are basically describing a 36-ary notation (as opposed to binary, decimal, or hexadecimal). I.e. the last letter represents (int value) mod 36, the second-but last letter represents (value/36)%36. Transform an integer into an array of six numbers from 0 to 35. Then map the resulting values such that 0=A, 25=Z, 26=0 and so on. Incrementing is just achieved by starting with an int value of 0, incrementing it, and transforming it into such a string after each increment. Yea you can probably also set up a 36-ary arithmetic such that you don't waste time between i and i+1, but I'd rather go with a brute force approach like that to begin with.