Jekyll/Liquid Templating: How to group blog posts by year?

Question

I\'m rewriting my blog to use Jekyll. Jekyll uses the Liquid templating language so it makes it a little more difficult to learn how to customize.

I\'d like to group

Answer 1

Did not much like the other answer so here's an alternative for you. Basic logic: Display year/month only if it "new":

{% assign var currentYear = 0 %}
{% assign var currentMonth = 0 %}
{% for post in site.posts  %}
{% capture year %}{{ post.date | date: "%Y" }}{% endcapture %}
{% capture month %}{{ post.date | date: "%B" }}{% endcapture %}

{% if currentYear != year %}
<div>
  <h2>{{ year }}</h2>
</div>
{% assign var currentYear = year %}
{% endif %}
{% if currentMonth != month %}
<div>
  <h3>{{ month }}</h3>
</div>
{% assign var currentMonth = month %}
{% endif %}
<p>{{ post.title }}</p>
{% endfor %}

Answer 2

These previous solutions are fantastic but luckily in late 2016, Jekyll added a group_by_exp filter that can do this much more cleanly.

{% assign postsByYear =
    site.posts | group_by_exp:"post", "post.date | date: '%Y'" %}
{% for year in postsByYear %}
  <h1>{{ year.name }}</h1>
    <ul>
      {% for post in year.items %}
        <li><a href="{{ post.url }}">{{ post.title }}-{{ post.date }}</a></li>
      {% endfor %}
    </ul>
{% endfor %}

Documentation can be found on the Jekyll Templates page.

Answer 3

Variation of Ankit R Gadiya's answer. The inner for loop was displaying the html code. I needed to de-indent it to get it to properly render the markup. I also added the post's excerpt:

{% assign postsByYear = site.posts | group_by_exp:"post", "post.date | date: '%Y'" %}
{% for year in postsByYear %}
  <h1>{{ year.name }}</h1>
  {% assign postsByMonth = year.items | group_by_exp:"post", "post.date | date: '%B'" %}

{% for month in postsByMonth %}
<h2>{{ month.name }}</h2>
<ul>
  {% for post in month.items %}
    <li>
      <a href="{{ post.url }}">{{ post.title }}</a>
      <br>{{ post.excerpt }}
    </li>
  {% endfor %}
</ul>

{% endfor %}
{% endfor %}

Example:

Answer 4

It can be done with much, much less Liquid code than in the existing answers:

{% for post in site.posts %}
  {% assign currentdate = post.date | date: "%Y" %}
  {% if currentdate != date %}
    <li id="y{{currentdate}}">{{ currentdate }}</li>
    {% assign date = currentdate %} 
  {% endif %}
    <li><a href="{{ post.url }}">{{ post.title }}</a></li>
{% endfor %}

This will return exactly the HTML specified in your question:

<li id="y2013">2013</li>
<li><a href="/2013/01/01/foo/">foo</a></li>
<li id="y2012">2012</li>
<li><a href="/2012/02/01/bar/">bar</a></li>
<li><a href="/2012/01/01/baz/">baz</a></li>

---

However, this is not the optimal solution, because the year numbers are "only" list items as well.
It's not much more Liquid code to put the year into a headline and to begin a new <ul> for each year's posts:

{% for post in site.posts %}
  {% assign currentdate = post.date | date: "%Y" %}
  {% if currentdate != date %}
    {% unless forloop.first %}</ul>{% endunless %}
    <h1 id="y{{post.date | date: "%Y"}}">{{ currentdate }}</h1>
    <ul>
    {% assign date = currentdate %}
  {% endif %}
    <li><a href="{{ post.url }}">{{ post.title }}</a></li>
  {% if forloop.last %}</ul>{% endif %}
{% endfor %}

The generated HTML:

<h1 id="y2013">2013</h1>
<ul>
<li><a href="/2013/01/01/foo/">foo</a></li>
</ul>
<h1 id="y2012">2012</h1>
<ul>
<li><a href="/2012/02/01/bar/">bar</a></li>
<li><a href="/2012/01/01/baz/">baz</a></li>
</ul>

---

You can also group by month and year instead (so that the headlines are February 2012, January 2012 and so on).

To do this, you just need to replace date: "%Y" (in the second line of both above examples) by date: "%B %Y".
(%B is the full month name, see the documentation)

Answer 5

<ul>
  {% for post in site.posts %}
      {% assign year = post.date | date: "%Y" %}

      {% if year != prev_year %}
        <h3>{{year}}</h3>
      {% endif %}

      <li>
        <span>{{ post.date | date: "%B %e, %Y" }}</span>
        <a href="{{ post.url }}">{{ post.title }}</a>
      </li>
      {% assign prev_year = year %}
  {% endfor %}
</ul>

Answer 6

Some solutions above are very complex but then as @Trevor pointed out that we can levarage Jekyll's group_by_exp filter. Also I liked the solution but what I needed was grouped by Year and then inside that list grouped by Month. So, I tweaked it a little bit.

{% assign postsByYear = site.posts | group_by_exp:"post", "post.date | date: '%Y'" %}
    {% for year in postsByYear %}
      <h1>{{ year.name }}</h1>
      {% assign postsByMonth = year.items | group_by_exp:"post", "post.date | date: '%B'" %}

      {% for month in postsByMonth %}
        <h2>{{ month.name }}</h2>
        <ul>
          {% for post in month.items %}
            <li><a href="{{ post.url }}">{{ post.title }}-{{ post.date }}</a></li>
          {% endfor %}
        </ul>

      {% endfor %}
    {% endfor %}