<div>
  <% @assignments.group_by(&:user).each do |user, assignments| %>
  <h4><%= user.name %></h4>
  <ul>
  <% assignments.each do |assignment| %>
    <li><%= link_to assignment.session.title, assignment.session %></li>
  <% end %>
  </ul>
  <% end %>
</div>