From: Barry Sperling <barry@...>
Date: 2004-09-17T05:09:56+09:00
Subject: 2-d arrays


	Reading the recent posts about ant-wars, I thought that, as a nuby, it 
would be interesting to try to recreate the ant-wars engine.  I looked 
at their code a little, and then started in.  I appreciate that James 
Edward Gray II provided us with his code, but I'll look at it after I've 
made more progress.
	I decided to create 2-d arrays to hold the data for given positions ( 
hexagonal blocks ).  One would hold the amount of food at a position, 
another would hold the traversability of it, etc.  My first attempt 
failed in a strange way and the point of this email is: why?

Method 1

cols = 10
empty_row_int = Array.new( cols, 0 )
$food_layout = Array.new
rows.times { $food_layout.push( empty_row_int ) }
puts $food_layout[ 0 ][ 0 ]  # 0
$food_layout[ 0 ][ 0 ] = 6   # SET FOOD ITEMS IN HEXAGON
puts $food_layout[ 0 ][ 0 ]  # 6
puts $food_layout[ 1 ][ 0 ]  # 6   WRONG!

	Then I read some archived emails from the group and found Matrix 
mentioned, but a matrix couldn't be changed by assignment.  However, it 
COULD be converted into an array, and so we get:

Method 2

require 'matrix'
maf = Matrix.zero( 10 )       # A SQUARE MATRIX, 10X10, INITIALIZED TO 0
$food2_layout = maf.to_a      # MATRIX TO ARRAY
puts $food2_layout[ 0 ][ 0 ]  # 0
$food2_layout[ 0 ][ 0 ] = 6   # SET FOOD ITEMS IN HEX
puts $food2_layout[ 0 ][ 0 ]  # 6
puts $food2_layout[ 1 ][ 0 ]  # 0

	Then I found another method was mentioned as listed in The Ruby Way:

Method 3

matrix = ( 0..9 ).map { ( 0..9 ).map { 0 } }

and when I use puts with the code as above, it works.
I understand Method 2, I "sort of" understand Method 3, but I don't know 
why "my" Method 1 doesn't work.
Thanks,
Barry