A solution for grouping items in loop with Timber and Twig - twig

Question

Often i need to do some tricky layout on dynamic elements like galleries.
Here's one example:
<ul>
<li class="slide">
<img src="img_01.jpg">
<img src="img_02.jpg">
</li>
<li class="slide">
<img src="img_03.jpg">
<img src="img_04.jpg">
</li>
<li class="slide">
<img src="img_05.jpg">
<img src="img_06.jpg">
</li>
</ul>
I've managed to do it with the following snippet. But i wanted some suggestions if possible about how to make it more flexible or more simple, like grouping by any number. Maybe using cycle() or any other method. I was getting strange results using the slice() or array[1:2] notation.
<ul>
{% for image in gallery %}
{% set current = loop.index %}
{% set next = current + 1 %}
{% if current is odd %}
<li class="slide">
{% for image in gallery %}
{% if loop.index in [current,next] %}
{% set th = TimberImage(image) %}
<img src="{{th.src}}">
{% endif %}
{% endfor %}
</li>
{% endif %}
{% endfor %}
</ul>
Any suggestions are welcomed.
Timber becomes very handy for quick in and out fixes with Timber::compile or custom themes with full routing. The purpose of the question is to create some snippet that can be reused.
Kudos to creators.
https://github.com/timber/timber

Answer 1

You can approach with the rest of the division with the following code (Here a working solutions):
{# number of element for every section #}
{% set section = 2%}
<ul>
{% for image in gallery %}
{% if loop.index % section == 1 %}
<li class="slide">
{% endif %}
{% set th = TimberImage(image) %}
<img src="{{th.src}}">
{% if loop.index % section == 0 or loop.last %}
</li>
{% endif %}
{% endfor %}
</ul>
You can easily reuse this code making a Twig macro using as parameter the gallery and the number of element for section (highlighted with the variable section

Answer 2

Here's the final result taking the suggestion of #Matteo for a macro:
https://gist.github.com/lithiumlab/5ee0454b0a77b1cc26fc0ce8ba52fd80
views/single.twig:
{% import 'utils.twig' as utils %}
{{utils.group_collection(gallery,3)}}
views/utils.twig:
{% macro group_collection(collection, groupby) %}
{% set section = groupby|default(2) %}
<ul>
{% for element in collection %}
{% if loop.index % section == 1 %}
<li class="group">
{% endif %}
{% set th = TimberImage(element) %}
<img src="{{th.src}}">
{% if loop.index % section == 0 or loop.last %}
</li>
{% endif %}
{% endfor %}
</ul>
{% endmacro %}