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

Perhaps you can simulate your multidimensional Array with a Hash. The Hash-key can by any Ruby object, so you could also take an array.

Example:

marray = {}
p marray[[1,2]]   #-> nil
marray[[1,2]] = :a
p marray[[1,2]]   #-> :a

Based on this idea you could define a new class.

Just a quick scenario:

=begin rdoc
Define a multidimensional array.

The keys must be Fixnum.

The following features from Array are not supported:
* negative keys (Like Array[-1])
* No methods <<, each, ...
=end
class MArray
  INFINITY = Float::INFINITY
=begin rdoc
=end
  def initialize(dimensions=2, *limits)
    @dimensions = dimensions
    raise ArgumentError if limits.size > dimensions
    @limits = []
    0.upto(@dimensions-1){|i|
      @limits << (limits[i] || INFINITY)
    }
    @content = {}
  end
  attr_reader :dimensions
  attr_reader :limits
=begin rdoc
=end
  def checkkeys(keys)
    raise ArgumentError, "Additional key values for %i-dimensional Array" % @dimensions if keys.size > @dimensions
    raise ArgumentError, "Missing key values for %i-dimensional Array" % @dimensions if keys.size != @dimensions
    raise ArgumentError, "No keys given" if keys.size == 0
    keys.each_with_index{|key,i|
      raise ArgumentError, "Exceeded limit for %i dimension" % (i+1) if key > @limits[i]
      raise ArgumentError, "Only positive numbers allowed" if key < 1

    }
  end
  def[]=(*keys)
    data = keys.pop
    checkkeys(keys)
    @content[keys] = data
  end
  def[](*keys)
    checkkeys(keys)
    @content[keys]
  end
end

This can be used as:

arr = MArray.new()
arr[1,1] = 3
arr[2,2] = 3

If you need a predefined matrix 2x2 you can use it as:

arr = MArray.new(2,2,2)
arr[1,1] = 3
arr[2,2] = 3
#~ arr[3,2] = 3  #Exceeded limit for 1 dimension (ArgumentError)

I could imagine how to handle commands like << or each in a two-dimensional array, but not in multidimensional ones.

Answer 2

Here is an implementation of a 3D array class in ruby, in this case the default value is 0

class Array3
 def initialize
   @store = [[[]]]
 end

 def [](a,b,c)
  if @store[a]==nil ||
    @store[a][b]==nil ||
    @store[a][b][c]==nil
   return 0
  else
   return @store[a][b][c]
  end
 end

 def []=(a,b,c,x)
  @store[a] = [[]] if @store[a]==nil
  @store[a][b] = [] if @store[a][b]==nil
  @store[a][b][c] = x
 end
end


array = Array3.new
array[1,2,3] = 4
puts array[1,2,3] # => 4
puts array[1,1,1] # => 0

Answer 3

There are two ways to initialize multi array (size of 2). All the another answers show examples with a default value.

Declare each of sub-array (you can do it in a runtime):

multi = []
multi[0] = []
multi[1] = []

or declare size of a parent array when initializing:

multi = Array.new(2) { Array.new }

Usage example:

multi[0][0] = 'a'
multi[0][1] = 'b'
multi[1][0] = 'c'
multi[1][1] = 'd'

p multi # [["a", "b"], ["c", "d"]]
p multi[1][0] # "c"

So you can wrap the first way and use it like this:

@multi = []
def multi(x, y, value)
  @multi[x] ||= []
  @multi[x][y] = value
end

multi(0, 0, 'a')
multi(0, 1, 'b')
multi(1, 0, 'c')
multi(1, 1, 'd')

p @multi # [["a", "b"], ["c", "d"]]
p @multi[1][0] # "c"

Answer 4

Use can also use the XKeys Gem.

require 'xkeys'

regular = [].extend XKeys::Auto
regular[1,2,3] = 4
# [nil, [nil, nil, [nil, nil, nil, 4]]]
regular[3,2,1, :else=>0] # 0
# Note: regular[1,2] is a slice
# Use regular[1,2,{}] to access regular[1][2]

sparse = {}.extend XKeys::Hash
sparse[1,2,3] = 4
# {1=>{2=>{3=>4}}}
path=[1,2,3]
sparse[*path,{}] # 4

Answer 5

Just a clarification:

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

is not at all the same as:

arr = Array.new(2, Array.new(2, 5))

in the later case, try:

arr[0][0] = 99

and this is what you got:

[[99,5], [99,5]]