Undefined method for matrix, string to matrix - ruby-on-rails

Question

I am trying to work with matrixes; I have a model that has an attribute called "board", and its just a 4x4 matrix. I display this board in my view. So far so good. When I click a button, I send the param "board" with, for example, this structure:
{"utf8"=>"✓", "game_master"=>{"board"=>"Matrix[[0, 0, 0, 0], [0, 0, 1, 1], [0, 0, 1, 0], [1, 1, 0, 0]]"}, "commit"=>"Yolo"}
On the other side, in the controller, I try to recreate this board by creating a new gamemaster with board = Matrix[[0, 0, 0, 0], [0, 0, 1, 1], [0, 0, 1, 0], [1, 1, 0, 0]]. So far so good (NOT, I know that the param[:board] is just a string, that's my problem). Then, later on, when trying to iterate the matrix, I get this error:
undefined method `each_with_index' for "Matrix[[0, 0, 0, 0], [0, 0, 1, 1], [0, 0, 1, 0], [1, 1, 0, 0]]":String
Clearly, I bound :board to a string NOT a matrix. How would I go around converting that string into the corresponding matrix?
Thanks
UPDATE:
game_masters_controller.rb
def step
#game_master = GameMaster.new(game_master_params)
#game_master.step
respond_to do |format|
format.js
end
end
And:
private
def game_master_params
params.require(:game_master).permit(:board)
end
game_master.rb
def initialize(attributes = {})
attributes.each do |name, value|
send("#{name}=", value)
end
if(self.board == nil)
self.board = get_new_board
end
end

Answer 1

Simply do:
arr = params[:game_master][:board].split(',').map(&:to_i).each_slice(4).to_a
# => [[0, 0, 0, 0], [0, 0, 1, 1], [0, 0, 1, 0], [0, 1, 0, 0]]
require 'matrix'
matrix = Matrix[*arr]
# => Matrix[[0, 0, 0, 0], [0, 0, 1, 1], [0, 0, 1, 0], [0, 1, 0, 0]]

Answer 2

Quick and dirty and not very secure:
class GameMaster
...
def board=(attr)
#board = eval attr
end
end

Answer 3

I would not run eval on something that gets submitted via a form. If the matrix is always 4x4, I would probably just submit the values in one long comma separated string like 0,0,0,1,1,1,0 .... Then I would use String#split to turn the large string into an array. Once you have one big array you could loop through it to generate an array of arrays that you can send to Matrix.new
string_params = 0,1,1,0,0,1
array_of_string = string_params.split(',')
array_of_arrays = array_of_string.each_slice(4).to_a
matrix = Matrix.new(array_of_arrays)
That should point you in the right direction.
Good luck!

Answer 4

Try this code:
(as the other answers mentioned, it's not secure to eval code coming from an input)
require 'matrix'
m = eval "Matrix[[0, 0, 0, 0], [0, 0, 1, 1], [0, 0, 1, 0], [1, 1, 0, 0]]"
=> Matrix[[0, 0, 0, 0], [0, 0, 1, 1], [0, 0, 1, 0], [1, 1, 0, 0]]
m.transpose
=> Matrix[[0, 0, 0, 1], [0, 0, 0, 1], [0, 1, 1, 0], [0, 1, 0, 0]]
Requiring the matrix.rb file will give you access to a lot of useful methods, check the documentation for further information.
http://ruby-doc.org/stdlib-2.1.0/libdoc/matrix/rdoc/Matrix.html