If Tyson Buzza don't mind, I would love to write this as my first PR as I
had used Elixir in work for two years and want to do a contribution. : P
On Thu, Oct 10, 2019 at 4:29 PM José Valim <jose.va...@plataformatec.com.br>
wrote:
> 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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Regards,
YongHao Hu
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