Adding a class to a post in Jekyll - jekyll

Question

I've got the following Jekyll index
---
layout: default
title: My favourite sandwiches
---
<section class="home">
{% for post in site.posts %}
<article class="column">
<img src="{{ post.image }}">
{{ post.title }}
</article>
{% endfor %}
</section>
My site will have 3 articles (blocks) next to each other, like tiles.
However, I would like to add a class on the first and third article tag so I can add different styling.
I wanted to know how to add this behaviour and if there is a way to index something eg. class="first" if index == 3/1
The html I wanted is to look something like this
<section class="home">
<article class="column first">
<img src="images/bigsandwich.jpg">
My big sandwich
</article>
<article class="column">
<img src="images/icecreamsandwich.jpg">
Icecream sandwich
</article>
<article class="column last">
<img src="images/sushisandwich.jpg">
Sushi sandwich
</article>
</section>
Thanks you for your patience and time.

Answer 1

Liquid's for loops have helper variables available, like forloop.first and forloop.last. See documentation here.
In your case, I would try:
---
layout: default
title: My favourite sandwiches
---
<section class="home">
{% for post in site.posts %}
{% if forloop.first %}
<article class="column first">
{% elsif forloop.last %}
<article class="column last">
{% else %}
<article class="column">
{% endif %}
<img src="{{ post.image }}">
{{ post.title }}
</article>
{% endfor %}
</section>