Liquid: Can I get a random element from an Array?

You may be able to do that just in Liquid, but it could less of generic solution like the one provided by @Brendan. According to this article, you can generate a random liquid number between min & max. So simply:

• Assign the min to 0 and max to your array's length.
• Loop over the array till you find your random number and pick you element.

Here is an example, get your random array index:

{% assign min = 0 %}
{% assign max = prefix.size %}
{% assign diff = max | minus: min %}
{% assign randomNumber = "now" | date: "%N" | modulo: diff | plus: min %}

Then find your random value:

{{ prefix[randomNumber] }}

You can create a plugin to get a random element. Something like this:

module Jekyll
  module RandomFilter
    # Use sample to get a random value from an array
    #
    # input - The Array to sample.
    #
    # Examples
    #
    #   random([1, 2, 3, 4, 5])
    #   # => ([2])
    #
    # Returns a randomly-selected item out of an array.
    def random(input)
      input.sample(1)
    end
  end
end

Liquid::Template.register_filter(Jekyll::RandomFilter)

Then do something like this in your template to implement:

{% assign myArray = '1|2|3|4|5 | split: '|' %}
{% assign myNumber = myArray | random %}

Liquid doesn't have a filter for picking a random element from an array or an integer interval.

If you want Jekyll to do that, you would have to create an extension to add that liquid filter.

However, I must point out that doing so would pick a random element every time the page is generated, but not every time the page is viewed.

If you want to get different random values every time you visit a page, your best option is using javascript and letting the client pick a random value. You can use liquid to generate the relevant javascript though.

The 2018 answer is

{% assign prefix = page.prefix | sample: 2 %}
{{ prefix[0] }}

As the OP asked about Jekyll, this can be found at: https://jekyllrb.com/docs/templates/