Re: [PHP] Too many arrays! My head is exploding!

On 29 May 2012 18:15, Gary <listgj-phpgene...@yahoo.co.uk> wrote:

> Okay, let's assume I have three "things", A, B, and C. I need to produce
> an array with a list of all possible combinations of them, however many
> there might be in those combinations: e.g. A, B, C, D, AB, AC, AD, BC,
> ABC (not sure if I've missed any!). Normally I'm pretty good at working
> this stuff out, but to be honest I'm struggling with this one, at least
> to do it in any kind of elegant way. Does anyone have any ideas?

Sure, but what you are asking for is a permutation and not a combination.

Here's a good read on the subject:

http://www.mathsisfun.com/combinatorics/combinations-permutations.html

Here's the deciding difference:

* If the order doesn't matter, then it's a combination.
* If the order does matter, then it's a permutation.

A combination of ABC is ABC.

However, the permutation of ABC is:

ABC
ACB
BAC
BCA
CAB
CBA

Oddly enough, a "combination lock" is a misnomer -- it should be a "permutation
lock" because the order of the "combination" does matter.

In any event, here's the code for as large a permutation as you may want:

http://www.webbytedd.com/b1/permutation/

Cheers,

tedd

_____________________
tedd.sperl...@gmail.com
http://sperling.com

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