From: Christopher Swasey <christopher.swasey@...>
Date: 2008-02-20T10:51:19+09:00
Subject: Re: IP Address to Decimal - is an one-liner possible?

On 2/19/08, Tiago Pinto <thpinto@gmail.com> wrote:
> Hi guys,
>
> A friend of mine needs to convert a string containing an IP Address
> (such as "127.0.0.1") to a decimal (that example would translate to
> 2130706433, <http://www.allredroster.com/iptodec.htm> said).
>
> We got a solution (that can easily be written in 2 lines):
>
> ip_d = 0 # let's start with zero
> ip_s = "127.0.0.1" # this our ip address as a string
> ip_a = ip_s.split(".") # now it's an array
> ip_i = ip_a.map{|i| i.to_i} # an array of ints
> ip_i.reverse! # let's reverse so we can use the array's indexes as the
> exponents when translating from base 256 to base 10)
> ip_i.each_with_index{|e,i| ip_d += e*(256**i)} # this is pure math,
> we're just changing bases here
>
> Our challenge (between me and my friend) was getting an one-liner for
> this. I think it'd be easy with something like Array#map_with_index or
> Array#inject_with_index because we use the indexes, here.
>
> What do you think? There's a way to do this? Is this just a silly question?

Use #inject, and instead of indexes rely on the size of the memo array:

"127.0.0.1".split(".").map { |i| i.to_i }.reverse.inject([]) { |memo,
part| memo << part * (256 ** memo.size) }.inject(0) { |memo, part|
memo += part }

Christopher