From: Stefano Crocco <stefano.crocco@...>
Date: 2008-04-07T01:18:38+09:00
Subject: Re: Problem while printing the content of an array, which is pointed by a variable

On Sunday 06 April 2008, Victor Reyes wrote:
> Team,
>
> I am trying to print the content of array, which is "addressed?" by a
> variable.
> Instead of getting the content of the array, I am getting its name.
> I think it is better to take a look at the code bellow. PLEEEEEEEEEEEEEASE
> Do not laugh at my code, I'm still a beginner!
>
> For example, for array @a1h, I expected to see: 1,0,0,0,7,0,0,0,4 but
> instead I see: @a1h.
>
> class SudokuBrute
>     def initialize
>
>     # The following sudoku is from:
> http://www.life.com/Life/sudoku/0,26379,,00.html
>     # This puzzle is rated as: easy
>     @a1h = [1,0,0,0,7,0,0,0,4]
>     @a2h = [0,0,0,6,0,4,0,5,0]
>     @a3h = [0,0,8,0,9,0,0,0,0]
>     @a4h = [6,0,0,9,0,0,0,1,5]
>     @a5h = [0,1,9,0,0,0,7,4,0]
>     @a6h = [5,3,0,0,0,1,0,0,8]
>     @a7h = [0,0,0,0,4,0,3,0,0]
>     @a8h = [0,7,0,5,0,8,0,0,0]
>     @a9h = [4,0,0,0,6,0,0,0,1]
>     end # End method initialize
>
>   def pGrid
>      for
>       x in 1..9 do
>         for
>           i in 1..9 do
>             arr = "@a" + i.to_s + "h"
>             puts arr
>         end
>     end
>   end  # End of method pGrid
> end    # End Class
>
> class Array
>   include Comparable
> end
>
> ##################
> ms = SudokuBrute.new
>
> # Output initial settings
> ms.pGrid

Well, it's doing what you're asking it to do. arr is not an array, it's a 
string like "@a1h". To achieve what you want, you can use 
instance_variable_get, which returns the content of the instance variable 
whose name is passed as argument:

arr = "@a" + i.to_s + "h"
puts instance_variable_get(arr)

The above suggestion works and only requires a small change in your code. Most 
likely, though, you should rethink the design of your class, replacing the 
nine instance variables with a single hash or array variable, like this:

@a = {
  :a1h => [1,0,0,0,7,0,0,0,4],
  :a2h => [0,0,0,6,0,4,0,5,0],
  :a3h => [0,0,8,0,9,0,0,0,0],
  :a4h => [6,0,0,9,0,0,0,1,5],
  :a5h => [0,1,9,0,0,0,7,4,0],
  :a6h => [5,3,0,0,0,1,0,0,8],
  :a7h => [0,0,0,0,4,0,3,0,0],
  :a8h => [0,7,0,5,0,8,0,0,0],
  :a9h => [4,0,0,0,6,0,0,0,1]
} 

This stores the content of the grid into a hash, where each entry represents a 
row. The keys are symbols (you can replace them with strings, if you like) and 
correspond to the names you gave to your instance variables. You can access a 
row with:

row = @a[:a3h]

The downside of using a hash is that entries aren't ordered. If you need to 
iterate on all the rows in order, this isn't the best solution. In this case, 
I'd use an array:

@a = [
  [1,0,0,0,7,0,0,0,4],
  [0,0,0,6,0,4,0,5,0],
  [0,0,8,0,9,0,0,0,0],
  [6,0,0,9,0,0,0,1,5],
  [0,1,9,0,0,0,7,4,0],
  [5,3,0,0,0,1,0,0,8],
  [0,0,0,0,4,0,3,0,0],
  [0,7,0,5,0,8,0,0,0],
  [4,0,0,0,6,0,0,0,1]
]

This way, rows can be accessed sequentially in the correct order, using 
@a.each or the for ... in syntax you used above . You can also access them 
using the [] syntax:

@a[3]

The downside is that you can no longer associate a key with the items.

I hope this helps

Stefano