Grouping and ordering entries by month

Question

I need to be able to group dates by their month but then order them by month too because the order they're inserted into the database in na super field table isn't always in date order.

So far, I have this:

{% set today = now|date('U') %}
{% set dates = [] %}
{% for date in entry.dates %}
    {% if date.start|date('U') >= today %}
    {% set dates = dates|merge([date]) %}
    {% endif %}
{% endfor %}

{% set datesByMonth = dates|group('start|date("F Y")') %}
{% for month, dates in datesByMonth %}
    {{ month }}
    dates stuff
{% endfor %}

which works fine except for the ordering.

I thought for the ordering, I might be able to do this:

{% for month, dates in datesByMonth|multisort(['start|date("c")']) %}
…
{% endfor %}

but that doesn't change the order. Am I doing that wrong or is there another way?

Answer 1

You could order the dates inside the for-loop, but I would order the dates before they're grouped, much simpler. You can do this in one clean pipeline, much easier to reason about and understand:

{% set datesByMonth = entry.dates
    |filter(date => date.start >= now)
    |sort((a, b) => a.start <=> b.start)
    |group(date => date.start | date('F Y'))
%}

First, the filter removes all dates before today, this means you can get rid of the first for-loop. Then, the array is sorted using the sort filter. Finally, the sorted array is grouped using the group filter. Since the array was already sorted, the grouped items will be sorted as well.

This assumes that entry.dates returns an array of DateTime objects. You can compare DateTime objects directly (both in PHP and Twig), so you don't need the date filter. If entry.dates is an array of something else (like dates string in a specific format), you can first map that to an array of DateTime objects using the map filter and the date function:

{% set datesByMonth = entry.dates
    |map(dateString => date(dateString))
    |filter(date => date.start >= now)
    |sort((a, b) => a.start <=> b.start)
    |group(date => date.start | date('F Y'))
%}