Deduplicating stash output

Question

I'm trying to create a dropdown filter based off a custom field in channel entries.

{exp:channel:entries channel="events"}

  {!-- Build the complete listing --}
  {exp:stash:append name="listing"}
    <li><a href="{title_permalink='events/detail'}">{title}</a></li>
  {/exp:stash:append}

  {!-- Build the dropdown filter options. This is what I want to contain unique values --}
  {exp:stash:append name="locations"}
    <option>{event_location}</option>
  {/exp:stash:append}

{/exp:channel:entries}

<select>
  {exp:stash:get name="locations"}
</select>

<ul>
  {exp:stash:get name="listing"}
</ul>

This might output something like:

<select>
  <option>USA</option>
  <option>USA</option>
  <option>Australia</option>
  <option>Canada</option>
</select>

<ul>
  <li><a href="...">First US Event</a></li>
  <li><a href="...">Second US Event</a></li>
  <li><a href="...">Australian Event</a></li>
  <li><a href="...">Canadian Event</a></li>
</ul>

However, I want the values in the {exp:stash:get name="locations"} to only be output once.
ie. USA once, not twice.
Is this possible?

Edit:
Turns out it does what I wanted on its own in the code I posted.
However my actual code had a {count} variable thrown in for testing.

{exp:stash:append name="locations"}
  <option>{count} - {event_location}</option>
{/exp:stash:append}

The {count} made each row unique.

Answer 1

If you can use the {exp:stash:get_list} tag pair you have access to the unique="yes" parameter. Might try it on the exp:stash:get tag.

Answer 2

You can use a query to do this instead of the channel:entries tag:

{exp:query sql="SELECT DISTINCT field_id_1 as location FROM exp_channel_data WHERE channel_id = '2'"}
    {exp:stash:append name="locations"}
            <option>{location}</option>
    {/exp:stash:append}
{/exp:query}

Change channel_id to match the ID of your events channel and field_id_1 to match your location field ID

Answer 3

Stash will automatically deduplicate the values if you are setting the exact same value more than once.