Removing duplicates from Liquid array

duplicates.html

{% assign array = 'c|c|b|b|a|a' | split: '|' %}
{% assign tags = array[1] %}

{% for item in array %}
    {% unless tags contains item %}
        {% capture tags %}{{ tags }}|{{ item }}{% endcapture %}
    {% endunless %}
{% endfor %}

{{ tags | split: '|' | sort | join: ', ' }}

keep_unique.rb

module Jekyll
    module KeepUnique
        def keep_unique(input)
            input.to_s.split('|').uniq
        end
    end
end

Liquid::Template.register_filter(Jekyll::KeepUnique)