more_efficient.rb

require 'pp'
class Jimmy

  def gencolumns
    a = []
    (0..8).each do |i|
      a[i] = []
    end
    base = 0
    (0..8).each do |i|
      (0..8).each do |j|
        a[i][j] = base + j
      end
      base += 9
    end
    pp a
  end
end

new = Jimmy.new
new.gencolumns