From: Stefano Crocco <stefano.crocco@...>
Date: 2007-10-17T20:51:12+09:00
Subject: Re: 2 dimensional array

Alle mercoledì 17 ottobre 2007, Shuaib Zahda ha scritto:
> Dear all
>
> I worked for quite some hours and i googled the two dimensional array in
> ruby and yet my problem is partially solved
>
> I want to declare 2-dimensional arrays it has 6 columns but uknow number
> of columns.
> i tried this way
> array = [][] # did not work
> array = [[],[]] # it works but only for two elements.
>
> another question I believe the answer is no but i want to confirm
> can we have multi-dimensional hash? :)
>
> any one has any idea to share
> Regards
> Shuaib

Ruby doesn't have 2-dimensional arrays, but you can use nested arrays to 
achieve the same effect. If you want an array with 6 columns and any number 
of rows, you can do something like:

a = Array.new(6){[]}

This creates an array of 6 elements, each of one contains an array. Each 
element represents a column. The entries of the column are stored into the 
nested array.

You can store entries like this:

a[2][3] = 1

This sets the element 3 of the row 2 to be one. 

Of course, this approach allows you to have columns with different sizes. For 
example, since each clumn is an array, you can do this:

a[1] << 2

This increases the size of the column 1 by one, by appending an element to it. 
If you want to avoid this, you can wrap the 2d array in a class:

class Array2D

  def initialize cols, default = nil
    @data = Array.new(cols){[]}
    @default = default
  end

  def append_row
    @data.each{|c| c << @default}
  end

  def [](col, row=nil)
    if row then @data[col][row]
    else @data[col].dup
    end
  end

  def []=(col, row, value)
    raise IndexError if col >= @data.size or row >= @data[0].size
    @data[col][row]=value
  end

  def each_col
    @data.each{|c| yield c.dup}
  end

  def each
    @data.each do |c|
      c.each{|i| yield i}
    end
  end

end

USAGE:

a = Array2D.new 3, :a
3.times{a.append_row}
a[0, 0] = :b
a[1, 2] = :c
p a[0]
p a[1]
p a[2]

Regarding your second question, what do you mean by "multidimensional hash"?

Stefano