Organize filtered entries by a specific category

Question

I have an array of products that has already been filtered by a brand category. I want to display them in a list ordered by a size category. This is working, but I think there must be a better way:

{% set productList = craft.entries(params) %} 
  {# where params includes a relatedTo parameter already #}

    {% for size in sizes %}
        {% for product in productList %}
            {% if product.sizeCategory.first.id == size.id %}
                {{ product.title }}<br />
            {% endif %}
        {% endfor %}
    {% endfor %}

Answer 1

First, grab the list of your products, filtered by category:

{% set productList = craft.entries(...).relatedTo(...) %}

Group all products by size using the group filter

{% set productList = productList | group('sizeCategory.first.whatever')

Now you have an array of arrays. The keys in the array hold the various values of the size variable, and the values of the array hold the arrays of entries within those size groups. (Within the groups, any ordering parameters you set on the original ElementCriteriaModel should be retained.)

To sort the groups according to the array size, you can use SuperSort's ksort functionality:

{% set productList = productList | supersort('ksort', false, SORT_NUMERIC) %}

To finish, just loop through this list of lists, outputting them in whatever style/markup you want:

{% for size, products in productList %}

    {{ size }}

    {% for product in products %}

        {{ size }}
        {{ product.whatever }}

    {% endfor %}

{% endfor %}

Answer 2

You should be able to order them using a combination of the order method (if needed) and group twig filter.

{% set productList = craft.entries.(params).order('title')|group('myCategoriesField.first().title') %}

The problem here is that the products might end up being displayed in the order that the size categories were created (i.e. postDate) and not the category 'size' title. If this is a problem then your solution may in fact be the only way. Have a look at this question for alternative answer and discussion of some of the issues.