From: Markus <markus@...>
Date: 2004-09-17T05:27:02+09:00
Subject: Re: 2-d arrays

I suspect method 1 doesn't do what you expect because you create one
single row and then make an array in which every element is that same
row.  Try instead:

Method 1'

cols = 10
$food_layout = Array.new
rows.times { $food_layout.push( Array.new( cols, 0 ) ) }
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 ]  # 0 

-- MarkusQ




On Thu, 2004-09-16 at 13:09, Barry Sperling wrote:
> 	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
> 
>