Sorting/grouping collections for an archive - html

Question

I am building my first site and am having a very difficult time grouping/sorting collections. The only success I have had is a list of files sorted alphabetically by subdirectory, then by files by their dates (seems to be the default) using:
<ul>
{% for page in site.collection_name | sort: weight %}
<h3>{{ page.title }}</h3>{{ page.category }}{{page.excerpt}}
{% endfor %}
</ul>
Weight (above) does not work. Neither did type, category, or any other variable I substituted.
My files are in subdirectories, and have permalinks as:
/collection_name/category_name/file_name/
Front matter includes:
title,
category,
layout,
type,
(tried several others)
The collection will have several file types such as:
articles,
videos,
research
What I want to accomplish is something that loops through my collection first for category, then by type. In very bad pseudo code:
<ul>
{% for page in site.{{category_name}} %}
<li><h2>{{category01}}</h2></li>
<ul>
{% for type in site.{{category_name.type}} | sort: date reverse%}
<li><h3>Articles</h3></li>
<li>{{ page.title }}{{page.excerpt}}</li>
<li><h3>Videos</h3></li>
<li>{{ page.title }}{{page.excerpt}}</li>
<li><h3>Research</h3></li>
<li>{{ page.title }}{{page.excerpt}}</li>
</uL>
<li><h2>{{category02}}</h2></li>
. . .
. . . {% endfor %}
Any help or direction will be appreciated.

Answer 1

Try to use group_by :
{% assign byCategory = site.collection_name | group_by: 'category' | sort: 'name' %}
{% for cat in byCategory %}
<h2>{{ cat.name | capitalize }}</h2>
{% assign byType = cat.items | group_by: 'type' %}
{% for type in byType %}
<h3>{{ type.name | capitalize }}</h3>
<ul>
{% for item in type.items %}
<li>{{ item.title }}</li>
{% endfor %}
</ul>
{% endfor %}
{% endfor %}
Note: this works with category: mycategory not with categories: [one, two]
If you want to specifically order types, you can do :
_config.yml
# this array determine types order
# a collection itm with non matching type will not be listed
types :
- articles
- videos
- research
code
{% assign byCategory = site.area | group_by: 'category' %}
{% for cat in byCategory %}
<h2>{{ cat.name }}</h2>
{% assign byType = cat.items | group_by: 'type' %}
{% for type in site.types %}
{% assign currentType = byType | where:"name", type | first %}
<h3>{{ currentType.name | capitalize }}</h3>
<ul>
{% for item in currentType.items %}
<li>{{ item.title }}</li>
{% endfor %}
</ul>
{% endfor %}
{% endfor %}