From: Shawn W_ <shawnw@...>
Date: 2009-09-16T20:33:46+09:00
Subject: Re: Making an array wrap, where last index + 1 = first index

Aldric Giacomoni wrote:
> def class Array2D < Array
>   def []( index )
>     super [] index % self.length
>   end
> end
> 
> How about that?

I thought there might be a neat mathematical way to do this but never 
would have found it by myself. Finding the remainder (% in Ruby) of:

array index / array size

works nicely.

I couldn't plug that code directly into my program and make it work, but 
I used the % technique. In my case it's a 2D array. I'm using the code 
by James Gray from the thread 
http://www.ruby-forum.com/topic/77572#850992, namely:

01 class Array2D
02
03   def initialize(width, height)
04   @data = Array.new(width) { Array.new(height) }
05   end
06
07  def [](x, y)
08    @data[x][y]
09  end
10
11  def []=(x, y, value)
12    @data[x][y] = value
13  end
14
15 end

I modified it to incorporate 'wrapping' like so:

01 class Array2D
02
03  attr_accessor :width, :height
04
05  def initialize(width, height)
06    @width = width
07    @height = height
08    @data = Array.new(@width) { Array.new(@height) }
09  end
10
11  def [](x, y)
12    x = x % @width
13    y = y % @height
14    @data[x][y]
15  end
16
17  def []=(x, y, value)
18    x = x % @width
19    y = y % @height
20    @data[x][y] = value
21  end
22
23 end

I'm not sure how impressed Rubyists would be with the neatness of this 
solution but it works.

Thx very much.
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