# Sorting DateTime lists with Enum.sort/2

`Enum.sort/1` puts January 31 after February 1:

```elixir
dates = [~U[2026-02-01 09:00:00Z], ~U[2026-01-31 09:00:00Z], ~U[2025-12-15 09:00:00Z]]

Enum.sort(dates)
#=> [~U[2026-02-01 09:00:00Z], ~U[2025-12-15 09:00:00Z], ~U[2026-01-31 09:00:00Z]]

Enum.sort(dates, DateTime)
#=> [~U[2025-12-15 09:00:00Z], ~U[2026-01-31 09:00:00Z], ~U[2026-02-01 09:00:00Z]]
```

Without a sorter, Elixir compares `DateTime` structs as plain maps, field by field, and `:day` comes before `:month` and `:year`. That's why the first result is ordered 1, 15, 31.

Passing the module makes `Enum` use `DateTime.compare/2`. The same works for `Enum.max/2`, `Enum.min_by/3` and friends, and `{:desc, DateTime}` flips the order. `Date`, `NaiveDateTime` and `Time` have the same problem and the same fix.

Mind you, `>` and `<` compare the same way, and the compiler didn't warn about `a > b` on two datetimes in Elixir 1.20.2. Use `DateTime.after?/2` and `DateTime.before?/2` for those checks.

https://hexdocs.pm/elixir/Enum.html#sort/2


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Created by: almirsarajcic
Date: September 23, 2026
URL: https://elixirdrops.net/d/fFwUcmbe