Ruby on Rails Tabular Data Ordered Column-wise

tabulate.rb

class Array

  # Converts a one dimensional array into a table with the given number of columns. Optionally transposes 
  # the result. Suited for output to an HTML table you want sorted vertically instead of horizontally. 
  # Pads correctly, i.e., each row/column has at most one empty cell. num_columns is the desired number 
  # of columns in the result, regardless if the table is transposed.
  def tabulate(num_columns, transpose=true)
    if transpose
      num_rows = num_columns
      num_columns = ((self.size - 1) / num_columns) + 1
    else
      num_rows = ((self.size - 1) / num_columns) + 1
    end
    num_rows_to_pad = self.size % num_columns > 0 ? num_rows - (num_columns - self.size % num_columns) : 0
    tabulated = []
    a_register = []
    # TODO: do this in chunks, not one element at a time
    self.each_with_index do |element, i|
      if a_register.size == num_columns - 1
        if num_rows_to_pad > 0 && tabulated.size + 1 > num_rows_to_pad
          a_register << nil
          tabulated << a_register
          a_register = []
          a_register << element
        else
          a_register << element
          tabulated << a_register
          a_register = []
        end
      else
        a_register << element
      end
    end
    if num_rows_to_pad > 0 && a_register.size < num_columns
      a_register << nil
      tabulated << a_register
    end
    if transpose
      tabulated.transpose
    else
      tabulated
    end
  end

end

tabulate_example.html.erb

<%# Example: turns [a, b, c, d, e, f, g, h, i, j] into %>
<%# [[a, b, c, d], [e, f, g, nil], [h, i, j, nil]] then transposes that into %>
<%# [[a, e, h], [b, f, i], [d, nil, nil]] for easy html table output into: %>
<%# a e h %>
<%# b f i %>
<%# c g j %>
<%# d %>
<%# note: in this example, i've added tabulate as method to Array class %>
<table>
  <% ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j"].tabulate(3, true).each do |row| %>
    <tr>
      <% row.each do |element| %>
        <td><%= element</td>
      <% end %>
    </tr>
  <% end %>
</table>