tap/app/views/products/index.html.erb

<h1>All products</h1>
<%= render partial: 'flash' %>

<div role="tabpanel">
  <!-- Nav tabs -->
  <ul class="nav nav-tabs" role="tablist">
    <% @categories.each do |o, i| %>
      <li role="presentation"<% if i.zero? %> class="active"<% end %>><a href="#<%= o %>" aria-controls="<%= o %>" role="tab" data-toggle="tab"><%= o.titleize %></a></li>
    <% end %>
  </ul>

  <!-- Tab panes -->
  <div class="tab-content">
    <br />
    <% @categories.each do |o, i| %>
      <div role="tabpanel" class="tab-pane<% if i.zero? %> active<% end %>" id="<%= o %>">
        <%= render @products.where(category: i) %>
      </div>
    <% end %>
  </div>

</div>