Group paginated messages by day

index.html.erb

<h1>Last activity</h1>
<% for day, messages in @messages_by_day -%>
  <h2><%= day %></h2>
  <ol>
  <%- for message in messages -%>
    <li><%= link_to message.title, message %></li>
  <%- end -%>
  </ol>
<% end -%>

<%= will_paginate @messages %>

messages_controller.rb

# fetch last 30 messages
@messages = Message.paginate :page => params[:page], :order => "created_at DESC"
# group them by date
@messages_by_day = @messages.group_by { |message| message.created_at.to_date }