class Roo::Base

def to_matrix(from_row = nil, from_column = nil, to_row = nil, to_column = nil, sheet = default_sheet)
  require 'matrix'
  return Matrix.empty unless first_row
  from_row ||= first_row(sheet)
  to_row ||= last_row(sheet)
  from_column ||= first_column(sheet)
  to_column ||= last_column(sheet)
  Matrix.rows(from_row.upto(to_row).map do |row|
    from_column.upto(to_column).map do |col|
      cell(row, col, sheet)
    end
  end)
end