difficulty modifying two dimensional ruby array

Question

Excuse the newbie question. I'm trying to create a two dimensional array in ruby, and initialise all its values to 1. My code is creating the two dimensional array just fine, but fails to modify any of its values.

Can anyone explain what I'm doing wrong?

  def mda(width,height)
     #make a two dimensional array
     a = Array.new(width)
     a.map! { Array.new(height) }

     #init all its values to 1
     a.each do |row|
       row.each do |column|
          column = 1
       end
     end
     return a
  end

Answer 1

It the line row.each do |column| the variable column is the copy of the value in row. You can't edit its value in such way. You must do:

def mda(width,height)
  a = Array.new(width)
  a.map! { Array.new(height) }
  a.each do |row|
    row.map!{1}
  end
  return a
end

Or better:

def mda(width,height)
  a = Array.new(width)
  a.map! { Array.new(height) }

  a.map do |row|
    row.map!{1}
  end
end

Or better:

def mda(width,height)
  a = Array.new(width){ Array.new(height) }
  a.map do |row|
    row.map!{1}
  end
end

Or better:

def mda(width,height)
  Array.new(width) { Array.new(height){1} }
end