From: w_a_x_man <w_a_x_man@...>
Date: 2010-07-15T23:35:08+09:00
Subject: Re: Return nothing when looking outside the bounds of 2D array?

On Jul 15, 5:49 am, w_a_x_man <w_a_x_...@yahoo.com> wrote:
> On Jul 14, 6:07 pm, w_a_x_man <w_a_x_...@yahoo.com> wrote:
>
> > On Jul 14, 3:56 pm, Shawn W_ <sha...@internode.on.net> wrote:
>
> > > 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
> > > --
> > > Posted viahttp://www.ruby-forum.com/.
>
> > Yields nil if out of bounds:
>
> > if ary[y]
> >   ary[y][x]
> > else
> >   nil
> > end
>
> def get2d ary, x, y
>   if ary[y]
>     ary[y][x]
>   else
>     nil
>   end
> end
>
> ary = [
>   %w(Z Z Z Z),
>   %w(Z H H Z),
>   %w(Z X Z Z) ]
>
> puts get2d( ary,2,1 )
> puts get2d( ary,1,2 )
> puts get2d( ary,3,3 )
> puts get2d( ary,4,0 )
>
> --- output ---
> H
> X
> nil
> nil

def get2d ary, x, y
  if ![x,y].include?(-1) and ary[y]
    ary[y][x]
  else
    nil
  end
end

ary = [
  %w(Z Z Z Z),
  %w(Z H H Z),
  %w(Z X Z Z) ]

puts get2d( ary,2,1 )
puts get2d( ary,1,2 )
puts get2d( ary,3,3 )
puts get2d( ary,4,0 )
puts get2d( ary,4,-1 )

--- output ---
H
X
nil
nil
nil