[Proposal] Enum.sort for Dates

[Josh Crews]

Current behavior:

iex(3)> [~D[2017-01-04], ~D[2017-04-03], ~D[2017-01-05]] |> Enum.sort

[~D[2017-04-03], ~D[2017-01-04], ~D[2017-01-05]]

Proposed:

iex(3)> [~D[2017-01-04], ~D[2017-04-03], ~D[2017-01-05]] |> Enum.sort

[~D[2017-01-04], ~D[2017-01-05], ~D[2017-04-03]]

What I'm currently doing is:

iex(4)> [~D[2017-01-04], ~D[2017-04-03], ~D[2017-01-05]] |> Enum.map(&(Date.to_erl/1)) |> Enum.sort |> Enum.map(&(Date.from_erl!/1))

[~D[2017-01-04], ~D[2017-01-05], ~D[2017-04-03]]

which is working great, but would be cool to have Enum.sort work on Date types too.

[Paul Schoenfelder]

Probably easier to use `Enum.sort_by(dates, &DateTime.to_unix/1)`, no?

Paul

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[Josh Crews]

Hi. I love Timex so much!

Regarding work around... I guess?

What do you think of the main thread question, "should Enum.sort work on Date types"?

On Friday, January 20, 2017 at 1:42:20 PM UTC-6, Paul Schoenfelder wrote:

Probably easier to use `Enum.sort_by(dates, &DateTime.to_unix/1)`, no?

Paul

On Fri, Jan 20, 2017 at 1:39 PM, Josh Crews <crews...@gmail.com> wrote:

Current behavior:

iex(3)> [~D[2017-01-04], ~D[2017-04-03], ~D[2017-01-05]] |> Enum.sort

[~D[2017-04-03], ~D[2017-01-04], ~D[2017-01-05]]

Proposed:

iex(3)> [~D[2017-01-04], ~D[2017-04-03], ~D[2017-01-05]] |> Enum.sort

[~D[2017-01-04], ~D[2017-01-05], ~D[2017-04-03]]

What I'm currently doing is:

iex(4)> [~D[2017-01-04], ~D[2017-04-03], ~D[2017-01-05]] |> Enum.map(&(Date.to_erl/1)) |> Enum.sort |> Enum.map(&(Date.from_erl!/1))

[~D[2017-01-04], ~D[2017-01-05], ~D[2017-04-03]]

which is working great, but would be cool to have Enum.sort work on Date types too.

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[José Valim]

Sorting in Elixir is based on the structure so there is no way Enum.sort can be made to work for DateTime. You need to give a sorter or an operation, like Paul described, if you would like to change its behaviour.

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

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[Paul Schoenfelder]

Sorry Josh, I should have replied to your original proposal. What I was getting at is that you can already use the existing Enum sorting functions with Dates, just by providing a sorter function, you don't have to convert to/from. As José mentioned though, there isn't any way to make Enum.sort/1 itself work on structs, it's up to the struct implementor to define functions which can be easily used with `Enum.sort_by` to make them sortable, such as `DateTime.to_unix`. There have been previous conversations on the mailing list about this subject, but I don't believe any of them got to a point where there was a viable implementation.

Paul

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[Ben Wilson]

See an earlier discussion on a similar idea: https://groups.google.com/forum/#!topic/elixir-lang-core/eE_mMWKdVYY