[ruby] Create two-dimensional arrays and access sub-arrays in Ruby

I wonder if there's a possibility to create a two dimensional array and to quickly access any horizontal or vertical sub array in it?

I believe we can access a horizontal sub array in the following case:

x = Array.new(10) { Array.new(20) }

x[6][3..8] = 'something'

But as far as I understand, we cannot access it like this:

x[3..8][6]

How can I avoid or hack this limit?

Here's a 3D array case

class Array3D
   def initialize(d1,d2,d3)
    @data = Array.new(d1) { Array.new(d2) { Array.new(d3) } }
   end

  def [](x, y, z)
    @data[x][y][z]
  end

  def []=(x, y, z, value)
    @data[x][y][z] = value
  end
end

You can access subsections of each array just like any other Ruby array. @data[0..2][3..5][8..10] = 0 etc

I'm quite sure this can be very simple

2.0.0p247 :032 > list = Array.new(5)

 => [nil, nil, nil, nil, nil] 

2.0.0p247 :033 > list.map!{ |x| x = [0] }

 => [[0], [0], [0], [0], [0]] 

2.0.0p247 :034 > list[0][0]

  => 0

Here is the simple version

 #one
 a = [[0]*10]*10

 #two
row, col = 10, 10
a = [[0]*row]*col

a = Array.new(Array.new(4))

0.upto(a.length-1) do |i|
  0.upto(a.length-1) do |j|
    a[i[j]] = 1
  end
end

0.upto(a.length-1) do |i|
  0.upto(a.length-1) do |j|
    print a[i[j]] = 1 #It's not a[i][j], but a[i[j]]
  end
  puts "\n"
end

You didn't state your actual goal, but maybe this can help:

require 'matrix'  # bundled with Ruby
m = Matrix[
 [1, 2, 3],
 [4, 5, 6]
]

m.column(0) # ==> Vector[1, 4]

(and Vectors acts like arrays)

or, using a similar notation as you desire:

m.minor(0..1, 2..2) # => Matrix[[3], [6]]

x.transpose[6][3..8] or x[3..8].map {|r| r [6]} would give what you want.

Example:

a = [ [1,  2,  3,  4,  5],
      [6,  7,  8,  9,  10],
      [11, 12, 13, 14, 15],
      [21, 22, 23, 24, 25]
    ]

#a[1..2][2]  -> [8,13]
puts a.transpose[2][1..2].inspect   # [8,13]
puts a[1..2].map {|r| r[2]}.inspect  # [8,13]

rows, cols = x,y  # your values
grid = Array.new(rows) { Array.new(cols) }

As for accessing elements, this article is pretty good for step by step way to encapsulate an array in the way you want:

How to ruby array

Here is an easy way to create a "2D" array.

2.1.1 :004 > m=Array.new(3,Array.new(3,true))

=> [[true, true, true], [true, true, true], [true, true, true]]