I love this. My suggestion is to add earliest(date, date) and
earliest(list_of_dates) and the same for latest. We need to add it to Time,
Date, NaiveDateTime and DateTime.
A PR is very appreciated.
*José Valim*
www.plataformatec.com.br
Skype: jv.ptec
Founder and Director of R&D
On Thu, Oct 10, 2019 at 5:15 AM Tyson Buzza <tyson.bu...@gmail.com> wrote:
> I have been using DateTime and NaiveDateTime alot over the last year and
> have found that using the compare function to involves some mental
> gymnastics. When using compare you often just want the most recent or
> oldest timestamp, or else you want to sort a list of timestamps.
>
> I am proposing four new functions for each module: earliest/2, latest/2,
> sort_earliest/2, and sort_latest/2. earliest/2 and latest/2 each take two
> DateTime structs and return the first/last time respectively. The
> sort_earliest/2 and sort_latest/2 functions take a list and an optional
> mapper, similar to the Enum.sort_by/2 function. sort_earliest/2 and
> sort_latest/2 will return the list in ascending/descending chronological
> order respectively.
>
> Example usage:
>
> ```
> start_time = DateTime.earliest(datetime1, datetime2)
> start_time = Enum.reduce(datetime_list, &DateTime.earliest/2)
> sorted_times = DateTime.sort_earliest(datetime_list)
> sorted_records = DateTime.sort_earliest(records, &(&1.timestamp))
> ```
>
> This example is a function that uses sort_earliest to check if a time is
> inside a given time range:
>
> ```
> def in_range(time_stamp, {start_time, end_time} = _range) do
> case sort_earliest([time_stamp, start_time, end_time]) do
> [^start_time, ^time_stamp, ^end_time] ->
> true
>
> _ ->
> false
> end
> end
> ```
>
> The implementation would be something simple like this:
>
> ```
> def sort_earliest(list, mapper \\ fn x -> x end) do
> Enum.sort_by(list, mapper, fn x, y ->
> :lt == DateTime.compare(x, y)
> end)
> end
>
> def earliest(%DateTime{} = datetime1, %DateTime{} = datetime2) do
> case DateTime.compare(datetime1, datetime2) do
> :gt ->
> datetime2
>
> _ ->
> datetime1
> end
> end
> ```
>
> Might need to make sure sort_earliest is an in place sort.
>
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