Jekyll - Get all posts that are in multiple categories

Question

I want to loop over all posts that are assigned category "foo" and category "bar" ..

{% for post in site.categories.foo and in site.categories.bar %}

Is this possible?

In my case "foo" as a "parent" category to "bar" ... /foo/bar/_posts

Thanks

Workable

Answer 1

Instead of looking through every post and matching with an or, you can filter by the first tag and then look for the second (and third, fourth, fifth...) tags:

{% for post in site.categories.fizz%}
    {% if post.categories contains "buzz" and post.categories contains "bang" %}
         <!--post has categories fizz AND buzz AND bang-->
        <li><a href="{{ post.url }}">{{ post.title }}</a></li>
    {% endif %}
{% endfor %}

This is a little more efficient than iterating over every single post, and it sets up an and relationship instead of an or relationship.

Hordein

Answer 2

It is fully possible: loop over all posts, and then select the wanted posts:

{% for post in site.posts %}
    {% if post.categories contains "foo" or post.categories contains "bar" %}
        <li><a href="{{ post.url }}">{{ post.title }}</a></li>
    {% endif %}
{% endfor %}

Equipage

I tried this but then my forloop.index gets off which I'm using to write some separator elements. – Workable

And in my use case it would be an "and" not an "or" – Workable

Could you please discribe how your posts are actually stored, and how your categories are defined? – Equipage

I did. They are organized by path as shown in the original question. – Workable

Yes, but how your YALM looks like? Is there something specific in your _config.yml about url ? – Equipage

Answer 3

Using the Where Expression filter in Jekyll.

Jekyll Liquid Filter Docs

Where Expression, Select all the objects in an array where the expression is true. 3.2.0

{{ site.members | where_exp:"item", "item.projects contains 'foo'" }}

So on my site I did:

_includes/clippings.html
...
{% capture _filter %}item.tags contains '{{ include.tag }}'{% endcapture %}

{% for clip in site.clippings | where_exp: 'item', _filter %}
  {{ clip.do_stuff }}
  # more html and stuff
{ endfor }

{% include clippings.html tag='foo' %}

In this case I need to specify the filter tag dynamically. And clippings is just a collection like posts.

If you want to filter by multiple static tags you could do something like:

{% for post in site.posts | where_exp: 'item', "item.tags contains 'foo'" | where_exp: 'item', "item.tags contains 'bar'" %}
  {{ post.do_stuff }}
{ endfor }

If you want to do multiple dynamic filter tags then you will need to do something similar to the capture stuff I did above.

I have not tested this, but it should filter posts by an arbitrary amount of filter tags.

{% assign posts = site.posts %}
{% filter_tags = 'foo, bar, buzz' | slipt: ', ' %}

{% for tag in filter_tags %}
  {% capture _filter %}item.tags contains '{{ tag }}'{% endcapture %}
  {% assign posts = posts | where_exp: 'items', _filter %}
{% endfor %}

{% for post in posts %}
  {{ post.do_stuff }}
{% endfor %}

However looping over the whole thing once and checking each post might be more efficient at that point.

Kehoe