Oh, I see why you called it sort_earliest, because you also want to allow a
function to be given, in the style of sort_by. I am not a big fan of
sort_earliest though.
What if we add only: DateTime.earliest(list_of_dates) and
DateTime.earliest(list_of_dates, fun)? You can always get the earliest of
two dates by passing it a list with two elements.
*José Valim*
www.plataformatec.com.br
Skype: jv.ptec
Founder and Director of R&D
On Thu, Oct 10, 2019 at 5:26 AM José Valim <jose.va...@plataformatec.com.br>
wrote:
> 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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>>
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