Filtering an array in a Liquid/Jekyll template

Question

Most Liquid "filters" are actually "map"s in the functional programming sense: you take an array, you apply a function to each element and return the transformed array. I'd like instead to "filter": I want to return only those items in the array that match a certain condition. How can I do that?

Specifically, I'm trying to improve this template:

Authors: 
{% for c in site.data["contributors"] %}
  {% assign contributor = c[1] %}{% if contributor.role contains "author" %}{{contributor.name.given}} {{contributor.name.family}}{% endif %}{% endfor %}

which, prettified, looks like this:

Authors: 
{% for c in site.data["contributors"] %}
  {% assign contributor = c[1] %}
  {% if contributor.role contains "author" %}
    {{contributor.name.given}} {{contributor.name.family}}
  {% endif %}
{% endfor %}

where its data looks like this:

ianbarber:
  name:
    given: Ian
    family: Barber
  org:
    name: Google
    unit: Developer Relations
  country: UK
  role:
    - engineer
  homepage: http://riskcompletefailure.com
  google: +ianbarber
  twitter: ianbarber
  email: [email protected]
  description: "Ian is a DRE"

samdutton:
  name:
    given: Sam
    family: Dutton
  org:
    name: Google
    unit: Developer Relations
  country: UK
  role:
    - author
  google: +SamDutton
  email: [email protected]
  description: "Sam is a Developer Advocate"

(example taken from here).

The problem with this approach is that a newline is output if the current element doesn't match the condition, as you can see in https://developers.google.com/web/humans.txt.

How can I fix this?

Answer 1

Jekyll 2.0 has a where filter. See docs. Example - from doc:

{{ site.members | where:"graduation_year","2014" }}
{{ site.members | where_exp:"item", "item.graduation_year == 2014" }}

Answer 2

If you want to get rid of the newline if the condition doesn't match, try to remove the unwanted newlines in the if and for clauses:

{% for c in site.data["contributors"] %}{% assign contributor = c[1] %}{% if contributor.role contains "author" %}
  {{contributor.name.given}} {{contributor.name.family}}{% endif %}{% endfor %}

That may not look nice in the source, but it will probably get rid of the newline in the output.

Note: I didn't try this, but similar rearranging helped me get rid of unwanted newlines. You may even have to put the {% if ... on the extreme left, so the indentation does not get included.