How can I keep duplicate elements from displaying?

I have a timeline page that has dates displayed based on time stamps from activities I have created. The activities are made with the Public Activity Rails gem. Example:

As seen in the example there are multiple dates that are displayed on the left in green. These dates are taken from the created_at time stamps for the activities and displayed in a user friendly format.

What is the best way to keep the duplicates from displaying. For example there are multiple June 3rd dates that I would like to display only once.

HTML for date elements (displayed in a loop):

<li class="time-label">
  <span class="bg-red">
   <%= activity_date(activity) %>
  </span>
</li>

Ruby Method to format the date:

  def activity_date(activity)
   local_date(activity.created_at)
  end

I was thinking of maybe having a conditional in Ruby or Javascript to limit the duplicates from displaying. Any suggestions?