grouped.erb

<%- array = [1,2,3,4,5,6,7] %>
<%- grouped = array.in_groups(3) %>
<table>
  <% grouped.first.each_with_index do |first_col, index| %>
    <tr>
      <td><%= first_col %></td>
      <td><%= grouped[1][index] %></td>
      <td><%= grouped[2][index] %></td>
    </tr>
  <% end %>
</tabl>