Ruby multidimensional array

Question

Maybe it\'s just my lack of abilities to find stuff here that is the problem, but I can\'t find anything about how to create multidimensional arrays in Ruby.

Could s

Answer 1

I had to reproduce PHP-style multidimensional array in Ruby recently. Here is what I did:

# Produce PHP-style multidimensional array.
#
# Example
#
# arr = Marray.new
#
# arr[1][2][3] = "foo"
# => "foo"
#
# arr[1][2][3]
# => "foo"

class Marray < Array
  def [](i)
    super.nil? ? self[i] = Marray.new : super
  end
end

Answer 2

Actually this is much quicker than the block method given above:

arr = Array.new(n, Array.new(n, Array.new(n,0.0))) 

arr[0][1][2] += 1

Answer 3

The method given above don't works.

n = 10
arr = Array.new(n, Array.new(n, Array.new(n,0.0))) 
arr[0][1][2] += 1
puts arr[0][2][2]

is equivalent to

n = 10
a = Array.new(n,0.0)
b = Array.new(n,a)
arr = Array.new(n, b) 
arr[0][1][2] += 1
puts arr[0][2][2]

and will print 1.0, not 0.0, because we are modifiyng array a and printing the element of array a.

Answer 4

Strictly speaking it is not possible to create multi dimensional arrays in Ruby. But it is possible to put an array in another array, which is almost the same as a multi dimensional array.

This is how you could create a 2D array in Ruby:

a = [[1,2,3], [4,5,6], [7,8,9]]

---

As stated in the comments, you could also use NArray which is a Ruby numerical array library:

require 'narray'
b = NArray[ [1,2,3], [4,5,6], [7,8,9] ]

---

Use a[i][j] to access the elements of the array. Basically a[i] returns the 'sub array' stored on position i of a and thus a[i][j] returns element number j from the array that is stored on position i.

Answer 5

It might help to remember that the array is an object in ruby, and objects are not (by default) created simply by naming them or naming a the object reference. Here is a routine for creating a 3 dimension array and dumping it to the screen for verification:

def Create3DimensionArray(x, y, z, default)
    n = 0                       # verification code only
    ar = Array.new(x)
    for i in 0...x
        ar[i] = Array.new(y)
        for j in 0...y
            ar[i][j] = Array.new(z, default)
            for k in 0...z      # verification code only
                ar[i][j][k] = n # verification code only
                n += 1          # verification code only
            end                 # verification code only
        end
    end
    return ar
end

# Create sample and verify
ar = Create3DimensionArray(3, 7, 10, 0)

for x in ar
    puts "||"
    for y in x
        puts "|"
        for z in y
            printf "%d ", z
        end
    end
end

Answer 6

you can pass a block to Array.new

Array.new(n) {Array.new(n,default_value)}

the value that returns the block will be the value of each index of the first array,

so..

Array.new(2) {Array.new(2,5)} #=> [[5,5],[5,5]]

and you can access this array using array[x][y]

also for second Array instantiation, you can pass a block as default value too. so

Array.new(2) { Array.new(3) { |index| index ** 2} } #=> [[0, 1, 4], [0, 1, 4]]