Add filter and grouping support

[haacked]

I had a case where I wanted to group a bunch of pages by a property. Here's a naive example of the type of code I would want to write:

{% for group in site.pages.filter(:enabled).group_by(:someProperty) %}
   <h2>{{ group.Name }}</h2>
   <ul>
   {% for item in group.Items %}
      <li>{{ item.FooBar }}</li>
    {% endfor %}
  </ul>
{% endfor %}

This could be a better way to handle grouping blog posts by dates too.

• group_by
• where

[benbalter]

Since jsonify dropped, the ability to filter would be absolutely killer. e.g., {{ site.pages | filter:"layout","license" | jsonify }} Perhaps a where filter would be a more Jekyll-y way?

[parkr]

This is a great idea! Would you filter only by category, or by anything in page.data?

[benbalter]

In my head, I was thinking it was similar to ruby's select behavior, or underscore's where. Iterate through an array of objects and return those objects where the given key matches the specified value.

[parkr]

@benbalter Hm, I think @haacked's idea of "group_by" would make more sense in this case, as it'd group by a key. Otherwise, we'd have to know both the key and the value. Syntax is doable, but would have to be like filter: "layout => license" and parsed as filter the given array such that only objects whose layout key is "license". I'd probably add two filters here:

• group_by
• filter (filter only by ==, or also by include??)

[haacked]

Would you filter only by category, or by anything in page.data?

Ideally anything in page.data. That'd make it much more powerful.

Also, I don't think select and where capture the group_by semantics. group_by is effectively an aggregation function. Not sure what that corresponds to in Ruby. Sorry. :)

[parkr]

@haacked #1788 has been merged.

[haacked]

Yay!

[haacked]

Someone on the twitters asked about sorting. I added it here, but should I create a new issue? Thoughts?

[parkr]

Please create a new issue :)