🔗 How to sort a list of structs or maps by two dates in Elixir

In this post, you’ll learn how to sort a list of structs (or maps) by two dates.

TL;DR

Elixir official Enum.sort/2 docs tell you how to sort by a date using the Date module, for example:

iex> Enum.sort([~D[2024-05-05], ~D[2024-05-01], ~D[2024-05-03]], {:asc, Date})
[~D[2024-05-01], ~D[2024-05-03], ~D[2024-05-05]]

Using descendant order:

iex> Enum.sort([~D[2024-05-05], ~D[2024-05-01], ~D[2024-05-03]], {:desc, Date})
[~D[2024-05-05], ~D[2024-05-03], ~D[2024-05-01]]

But, what when you need to use a key from a map?

Elixir’s Enum.sort_by/3 accepts a mapper function to extract the said value. From the docs:

This function maps each element of the enumerable using the provided mapper function. The enumerable is then sorted by the mapped elements using the sorter, which defaults to :asc and sorts the elements ascendingly.