From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2011-05-25T19:32:26+09:00
Subject: Re: 2d array of hashes

On Wed, May 25, 2011 at 12:23 PM, Alex Raduca
<alexandru.raduca@gmail.com> wrote:
> Hi,
>
> I am trying to solve the Sudoku Ruby Quiz using a 2d array of hashes
> data model but I probably keep doing something wrong since the hashes
> are referenced at row level(last row of the sudoku matrix is
> referenced).
>
> Could I get a hint on where I should insert the Hash.new when dealing
> with 2d arrays. I have googled it but I could only find simple array of
> hashes examples.

So, what is the data model you want? A different hash for each cell?
Then there is a problem here:

> # creates sudoku matrix and fills it in with data
> sudoku=Array.new(9,Array.new(9))

This creates an array of size 9, pointing 9 times to the same array. Check it:

ruby-1.8.7-p334 :001 > a = Array.new(9, Array.new(9))
ruby-1.8.7-p334 :002 > a[0].object_id
 => -611740938
ruby-1.8.7-p334 :003 > a[1].object_id
 => -611740938

So, if you add a hash to that inner array, all your rows will have the
same hash.
Try this:

sudoku = Array.new(9) { Array.new(9)}

or if you want to assign an empty hash right away:

sudoku = Array.new(9) { Array.new(9) {{}}}

now, each position in the array of arrays has its own independent hash:

ruby-1.8.7-p334 :003 > sudoku[0][0][:possibilities] = [1,2,3,4,5,6,7,8,9]
 => [1, 2, 3, 4, 5, 6, 7, 8, 9]
ruby-1.8.7-p334 :004 > sudoku
 => [[{:possibilities=>[1, 2, 3, 4, 5, 6, 7, 8, 9]}, {}, {}, {}, {},
{}, {}, {}, {}], [{}, {}, {}, {}, {}, {}, {}, {}, {}], [{}, {}, {},
{}, {}, {}, {}, {}, {}], [{}, {}, {}, {}, {}, {}, {}, {}, {}], [{},
{}, {}, {}, {}, {}, {}, {}, {}], [{}, {}, {}, {}, {}, {}, {}, {}, {}],
[{}, {}, {}, {}, {}, {}, {}, {}, {}], [{}, {}, {}, {}, {}, {}, {}, {},
{}], [{}, {}, {}, {}, {}, {}, {}, {}, {}]]

Jesus.