From: Todd Benson <caduceass@...>
Date: 2008-03-01T03:57:59+09:00
Subject: Re: Beginner Help with code example from book

On Fri, Feb 29, 2008 at 10:58 AM, Joseph L. Casale
<jcasale@activenetwerx.com> wrote:
> > > def continent_size world, x, y
>  > > if world[y][x] != ' land'
>  > > # Either it' s water or we already
>  > > # counted it, but either way, we don' t
>  > > # want to count it now.
>  > > return 0
>  > > end
>  > > :
>  > > world[y][x] = ' counted land'
>  >
>  > The world is changed.  When ' land' is counted, it turns into ' counted
>  > land' so on iteration, the "if" sees that it is not land and returns 0.
>  >
>  > --
>  > Posted via http://www.ruby-forum.com/.
>
>  Appreciate the pointer, thanks for bearing with me :)
>  Why has the author reversed the "X" and "Y"? on a square world it would not matter, but... Was there any significance to this?

I'm pretty sure it doesn't matter on any surface as long all tiles are
described in 2 dimensions (which they would have to, if you use a grid
of x's and y's.)  Think, for example, the surface of a 3-D globe cut
up into 4-sided tiles of different size.  The only drawback is that
you have to pick poles to topologically shrink a sphere into a surface
(this is often done by turning it into a torus/donut, but doesn't have
to be)

I haven't read Pine's book, but the x's and y's switcheroo can be
explained, I suppose, like this...

On a mathematical graph, a larger x means further right, and a larger
y means further up.  In a computer image, you have to remember, of
course, larger y usually means further down.

So, think of [0,3].  On an xy grid, that point would lie 3 units up on
the vertical axis.

For a multi-dimensional array [0,3] refers to the zeroth array, third
item (or, first array and fourth item, depending on how your mind
works).

In your visual multi-dimensional array world map, that would be the
fourth tile to the right, which would -- at least for most people --
be the x dimension, and not the y.

Hope that makes some sense,
Todd