Implement group_by in with_scope?

[danielmyasnikov]

Looking for something that has functionality:

{% with_scope group_by: category_id %}
    {% for group in content.posts %}
       {% for post in group %}
         {% post.title %}
       {% endfor %}
    {% endfor %}
{% endwith_scope %}

I have seen that it doesn't exist, however how would you implement it?

[danielmyasnikov]

group_by can be similar to Array#group_by method