How to specify multiple authors for a single post, then count the posts each author is related to?

Question

What I'm trying to do:

I'm trying to create a list for the posts each author has written. This is a problem since each post should be able to specify multiple authors.

Let's say we have 3 posts in total and 3 authors in total.

Edit 1: as suggested in the answers this is best done by listing the authors in a front matter list instead of a CSV string. So,

Like this

Post:

---
title: post
authors:
  - foo
  - bar
---

instead of like this:

Post:

---
title: post
authors: [foo, bar]
---

Problem setup:

(edited, according to Edit 1)

Post 1:

---
title: post1
authors:
  - foo
  - bar
---

Post 2:

---
title: post2
authors:
  - foo
  - bar
---

Post 3:

---
title: post3
authors:
  - john doe
  - bar
---

Out:

bar (3) 
john doe (1)
foo (2)

A click on the author should then result in all posts getting displayed.

Alternatively an array can be displayed like this, but it's not helping the case, just an equivalent style.

What I tried

I did the same with categories and tags and this algorithm worked like a charm. However, replacing site.categories with site.authors is somehow not supported.

returns:

Liquid Exception: 0 is not a symbol nor a string in authors.html

I suppose this is due to the nature of categories and tags being arrays by default. I think it would help to be able to set the front matter tag authors as an array somehow. I suppose this is done in _config.yml, but I busted by head in with it.

As of now I got as far as coming up with a way to target individual authors in an array, but I'm far from being able to list them individually and counting them up. I suppose I'm limited due to the nature of authors not being an array by default, otherwise implementations like this one would work with custom front matter variables like authors, but they don't.

What I meant (when I said "As of now"):

{% for post in site.posts %}
    <li><a href="{{ SITEURL }}/{{ author.url }}">{{ post.authors }}</a> ({{ post.authors[0] }})</li>
{% endfor %}

Out:

foobar (foo)
foobar (foo)
john doebar (john doe)

Afterall, I think I'm missing something here. I'm probably not the first one who tried this but the only documentation I found was from people who attempted what I'm trying but didn't really get there.

This user for example created a way to count users, but when used with site.authors

it returns the array size == 0-if clause:

No author

It seems like a simple thing, but for some reason isn't. At least for me.

Edit 2:

based on Kieths answer I came closer to getting there, but I have issues with creating an emphty array. According to this issue in Jekyll this seems to be a problem in general. However a workaround seems to be to assign a variable and split it with an emphty tag. Currently I struggle with adding authors to the array so I can assess it's size.

{% assign authors = site.posts | map: 'authors' | uniq %}
{% assign authorCount = '' | split: '' %}

  <div class="softwaretitle">
    {% for author in authors %}
      <a>{{ author }}</a>


      {% for post in site.posts %}
        {% for post_author in post.authors %}
          {% if post_author == author %}

            {% assign authorCount = authorCount | push author %}
            <a>({{ page.authorCount | size }})</a>

          {% endif %}
        {% endfor %Edit 2:}
      {% endfor %}
    {% endfor %}
  </div>

Out:

Error: Liquid error (.../_includes/authors.html line 14): wrong number of arguments (given 1, expected 2) included Error: Run jekyll build --trace for more information.

Line 14:

{% assign authorCount = authorCount | push author %}

Edit 3:

At last, the final result (without link to the post list, but thats details)

<!-- Get a list of unique authors -->
  {% assign authors = site.posts | map: 'authors' | uniq | sort%}
  {% assign author_post_count = 0 %}
  {% for author in authors %}
          {% assign author_post_count = 0 %}

    <div class="">
      <li><a>{{ author }}
      {% for post in site.posts %}

        {% for post_author in post.authors %}
          {% if post_author == author %}
          {% assign author_post_count = author_post_count | | plus: 1 %}

          {% endif %}

        {% endfor %}
      {% endfor %}
      <span>&nbsp ({{ author_post_count }})</span></a></li>
    </div>
{% endfor %}

Out:

bar (3) 
john doe (1)
foo (2)

Answer 1

Updated answer:

To get a list of authors (without duplicates) and including the total number of posts the author has contributed to, together with a list of posts' titles and a link to the posts.

  {% assign authors = site.posts | map: 'authors' | uniq %}

  {% for author in authors %}
  {% assign author_post_count = 0 %}
   {% for post in site.posts %}
    {% if post.authors %}
     {% for post_author in post.authors %}
      {% if post_author == author %}
        {% assign author_post_count = author_post_count | plus: 1 %}
      {% endif %}
     {% endfor %}
    {% endif %}
  {% endfor %}
      <h2>{{ author }} - {{ author_post_count }}</h2>
      {% for post in site.posts %}
       {% if post.authors %}
        {% for post_author in post.authors %}
          {% if post_author == author %}
           {% assign author_url_query =  author | replace: ' ', '-' %}
            <a href="{{ post.url }}" title="A posts {{ author }}">
             {{ post.title }}
            </a>
          {% endif %}
        {% endfor %}
        {% endif %}
      {% endfor %}
  {% endfor %}

If instead, you want to have a page per author that includes a list of posts written by them (automatically generated), you will need to extend Jekyll through a custom plugin. This is very possible if you have experience with the Ruby programming language. This is a very close example: https://github.com/avillafiorita/jekyll-datapage_gen and you can simply remove the _config data requirements and hardcode the directory names and permalinks :)

Answer 2

Problem :

• on a post : print author(s) + number of posts written and link to the authors page
• on an author's page : print author's datas + list written posts

Solution

We already have posts that are described like this :

---
title: post2
authors: [foo, bar]

# or with the alternate YAML array syntax
authors:
  - foo
  - bar

---

For authors, we can user a specific collection that will automatically generate author's page.

In _config.yml :

collections:
  authors:
    output: true

defaults:
  - scope:
      type: authors
    values:
      layout: authors

An author's page can be described like this :

_authors/foo.md

---
uid : foo
firstname: John
lastname: Foo
---

Some bio here ...

Posts List (index or any page):

{% assign posts = site.posts %}
{% comment %}
or {% assign posts = paginator.posts %} if you use pagination
{% endcomment %}

<ul>
{% for post in posts %}
  <li>
    <a href="{{ site.baseurl }}{{ p.url }}">{{ p.title }}</a>
    <br>{% include authors.html post=post %}
  </li>
{% endfor %}
</ul>

We will also use our authors include in _layouts/post.html

...
    <h1 class="post-title" itemprop="name headline">{{ page.title | escape }}</h1>
    <p>{% include authors.html post=page %}</p>
...

Now the magic : _includes/authors.html

{% assign post = include.post %}

{% comment %}## if we have a least one author in post authors array {% endcomment %}
{% if post.authors and post.authors != empty %}

  {% comment %} ## We will build a string for each author,
                   store it in authorsArray
                   then reassemble it at the end {% endcomment %}
  {% assign authorsArray = "" | split: "" %}

  {% for author in post.authors %}

    {% comment %}## Count posts for current author {% endcomment %}
    {% assign authorsPostsCount = site.posts | where_exp: "post", "post.authors contains author" | size %}

    {% comment %}## Get authors data based on uid matching in the collection {% endcomment %}
    {% assign authorsDatas = site.authors | where: "uid", author | first %}

    {% if authorsDatas %}
      {% capture authorString %}
      <a href="{{ site.baseurl }}{{ authorsDatas.url }}">{{ authorsDatas.firstname }} {{ authorsDatas.lastname }} ({{ authorsPostsCount }}) </a>
      {% endcapture %}

    {% else %}
      {% comment %}## No entry for this author in the collection
                   ## or author spelling is wrong {% endcomment %}
      {% capture authorString %}
        {{ author | capitalize }} ({{ authorsPostsCount }})
      {% endcapture %}
    {% endif %}

    {% comment %}## Push result in authorsArray {% endcomment %}
    {% assign authorsArray = authorsArray | push: authorString %}
  {% endfor %}
  {% comment %}## Create a sentence with array elements {% endcomment %}
  by {{ authorsArray | array_to_sentence_string }}
{% endif %}

_layouts/author.html

---
layout: default
---

<h1>{{ page.firstname }} - {{ page. lastname }}</h1>

{% assign authorsPosts = site.posts | where_exp: "post", "post.authors contains page.uid" %}

<ul>
  {% for p in authorsPosts %}
    <li><a href="{{ site.baseurl }}{{ p.url }}">{{ p.title }}</a></li>
  {% endfor %}
</ul>