groupby complex attributes

[tcurdt]

I have a list of objects. These objects have a date attribute. I want to group by year.
Something along the lines of the following would be nice.

for year, posts in collections.post | groupby("date.year")

But it begs the question how to deal with transforms that need to happen before the grouping.
Is there a way to use groupby like this?

[mattradford]

Oh man, this is exactly the problem I'm trying to solve.

[mattradford]

@tcurdt This may help: https://stackoverflow.com/questions/12764291/jinja2-group-by-month-year

[tcurdt]

@mattradford That's exactly what I was referring to with date.year above ;) Unfortunately that does not work (for me).

[justinfagnani]

Looking at the underlying groupBy code here: https://github.com/mozilla/nunjucks/blob/master/nunjucks/src/lib.js#L172

It takes a function, so you can write a generic getPath function that returns a function to get the value you want to group on. Just verified that this works. Here's my getPath:

    const getPath = (path) => {
      const parts = path.split('.');
      return (value, i) => {
        let o = value;
        for (const p of parts) {
          if (o == null) {
            return;
          }
          o = o[p];
        }
        return o;
      };
    }

[tcurdt]

@justinfagnani The function is straight forward - but the question is how this should look like in the expression.

[justinfagnani]

The depends on how you get the function as data into your template. I'm using eleventy, and putting the function into a docs object. My template looks like:

{% for group, examples in collections.examples | groupby(docs.getPath('data.group')) %}
...
{% endfor %}

[anaurelian]

This is a filter I'm using for Nunjucks in Eleventy:

groupByEx: function (arr, key) {
    const result = {};
    arr.forEach(item => {
        const keys = key.split('.');
        const value = keys.reduce((object, key) => object[key], item);

        (result[value] || (result[value] = [])).push(item);
    });
    return result;
}

Sample (actual) usage:

for categoryName, articles in productArticles | groupByEx("data.categoryName")

Acknowledgement: Code based on whatterz/includes.js

[tcurdt]

@anaurelian that's already pretty slick - but it would need a special case for dates I guess.