From: Martin DeMello <martindemello@...>
Date: 2008-07-30T06:26:28+09:00
Subject: Re: the old sorting ip addresses problem

On Tue, Jul 29, 2008 at 2:19 PM, matu <m@t.u> wrote:
> i am sure there has to be some ruby way of doing this in a really simple way...
> i came up with this, but i am sure there is some other way that is much cleaner.
>
>>> a = ["5.100.200.50", "10.150.50.1", "10.150.50.2", "10.150.51.1", "19.18.16.15", "192.168.0.1"]
> => ["5.100.200.50", "10.150.50.1", "10.150.50.2", "10.150.51.1", "19.18.16.15", "192.168.0.1"]
>>> a.sort {|a1, a2| y = [a1, a2].map {|addr| x = 0; addr.split('.').reverse.each_with_index {|n, i| x = x + n.to_i * (256 ** (i))}; x}; y.last <=> y.first}
> => ["192.168.0.1", "19.18.16.15", "10.150.51.1", "10.150.50.2", "10.150.50.1", "5.100.200.50"]

a.sort_by {|x| x.split(/\./).map {|i| i.to_i}}.reverse

=> ["192.168.0.1", "19.18.16.15", "10.150.51.1", "10.150.50.2",
"10.150.50.1", "5.100.200.50"]

This relies on the fact that ruby has built-in array sorting, where
it'll sort by the first element, then break ties on the second
element, and so on, and a built-in sort_by function, that transforms a
collection according to the block given, and sorts by the transformed
values.

martin