Loop trough collections of products - html

Question

I'm trying to loop through all the collections that a set of products is part of. This is my code:
<div class="container model-collection">
<h1>{{ collection.title }}</h1>
{% paginate collection.products by 12 %}
<div class="grid collection-products-container">
<ul>
{% for product in collection.products %}
{% for collection in product.collections %}
<li>{{ collection.title }}</li>
{% endfor %}
{% endfor %}
</ul>
</div>
{% if paginate.pages > 1 %}
{% include 'pagination' %}
{% endif %}
{% endpaginate %}
</div>
This works fine, however if two products are part of the same collection it lists that collection twice. So I need to limit the loop that it only shows each collection once.
I've tried to do it like this:
<div class="container model-collection">
<h1>{{ collection.title }}</h1>
{% assign model = collection.title %}
<div class="grid collection-products-container">
<ul>
{% for product in collection.products %}
{% assign seen_collections = "" %}
{% for collection in product.collections %}
{% unless seen_collections contains collection %}
{% assign seen_collections = seen_collections | append: "," | append: collection %}
<li>{{ collection.title }}</li>
{% endunless %}
{% endfor %}
{% endfor %}
</ul>
</div>
</div>
But this only returns one of the collections twice and none of the others. Any ideas how to do this?

Answer 1

You can get an aggregate list of nested properties by using the map filter in your Liquid code, and the map filter lets you drill into nested objects quite efficiently.
So to get an array of all the unique collection handles used by all the products in your collection, we can quickly get the info we want as:
{% assign collection_handles = collection.products | map: 'collections' | map: 'handle' | uniq %}
This creates an array of all the collection handles of all the products inside the collection, then reduces them to just the unique ones (using the uniq filter). Note: uniq needs to work with a number, string, or other simple field - which is why we needed an array of collection handles, not an array of collection objects.
So now you can do your loop as:
{% for handle in collection_handles %}
{% assign collection = collections[handle] %}
<!-- All your awesome stuff here -->
{% endfor %}
Hope this helps!