From: Robert Klemme <shortcutter@...>
Date: 2010-07-19T16:43:50+09:00
Subject: Re: Return nothing when looking outside the bounds of 2D array?

2010/7/14 Shawn W_ <shawnw@internode.on.net>:
> I have a 2D Array. I have written a method
> Array2D.adjacent(x,y,direction) that returns the adjacent cell to x,y in
> the direction given. How do I deal with the boundary conditions without
> receiving an error message.
>
> For example, if I refer to a cell on the top row, and look north there
> will be nothing there, and my program falls over.
>
> I will be creating methods that run over the whole 2D array, replacing
> things in random directions, so when it randomly hits a boundary I need
> my program to ignore cells outside the boundary.
>
> How can I do this? Thx

Did anybody suggest modulo operator so far?  I only glanced over
replies so I might actually have overseen something.  Anyway, you can
see it working here:

irb(main):001:0> a = Array.new(10){|row| Array.new(10) {|col|
"#{row},#{col}"}};nil
=> nil
irb(main):002:0> a.size
=> 10
irb(main):003:0> a[0].size
=> 10

irb(main):012:0> 15.times {|i| printf "%2d %p %p\n",i,a[0][i % 10],a[i % 10][0]}
 0 "0,0" "0,0"
 1 "0,1" "1,0"
 2 "0,2" "2,0"
 3 "0,3" "3,0"
 4 "0,4" "4,0"
 5 "0,5" "5,0"
 6 "0,6" "6,0"
 7 "0,7" "7,0"
 8 "0,8" "8,0"
 9 "0,9" "9,0"
10 "0,0" "0,0"
11 "0,1" "1,0"
12 "0,2" "2,0"
13 "0,3" "3,0"
14 "0,4" "4,0"
=> 15

Kind regards

robert


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