> TIL: I knew about Enum.into but not Map.new.
Same here! :)
Thank you Jose, this suggestion solves the use cases I had in a very simple
and natural way! I agree there is no need to add a new function.
Le samedi 25 juillet 2020 16:34:42 UTC+9, Zach Daniel a écrit :
>
> TIL: I knew about Enum.into but not Map.new.
>
> On Sat, Jul 25, 2020 at 3:08 AM José Valim <jose...@dashbit.co
> <javascript:>> wrote:
>
>> Hi Sabiwara,
>>
>> This is very close to Map.new/2 (and Enum.into/3):
>>
>> User |> Repo.all() |> Map.new(fn user -> {user.id, user} end)
>>
>> So my suggestion is to use Map.new/2 instead of adding a new function. :)
>>
>> Thanks for the proposal!
>>
>> On Sat, Jul 25, 2020 at 5:15 AM Sabiwara Yukichi <sabi...@gmail.com
>> <javascript:>> wrote:
>>
>>> Thank you, I'm glad to see I'm not the only one finding myself needing
>>> this :)
>>>
>>> > I think that we should keep the first value found for each key
>>> I really wasn't sure about which one would be more consistent with other
>>> Elixir APIs, I actually also have a branch keeping the first occurrence
>>> https://github.com/elixir-lang/elixir/compare/master...sabiwara:enum_key_by_first?expand=1
>>>
>>> Le samedi 25 juillet 2020 11:47:55 UTC+9, Zachary Daniel a écrit :
>>>>
>>>> I like it, I write this function by hand all the time. I like the name,
>>>> and I think that we should keep the first value found for each key.
>>>>
>>>> On Friday, July 24, 2020 at 10:34:27 PM UTC-4 sabi...@gmail.com wrote:
>>>>
>>>>> Hi! I would like to propose introducing an `Enum.key_by/3` function
>>>>> (name to be discussed) that would return a map where:
>>>>> - each key is the result of the first callback applied to an item
>>>>> - the value is the result of the second callback applied to the item
>>>>> (identity by default)
>>>>>
>>>>> It would basically be a copy of Enum.group_by/3 keeping only the last
>>>>> (or first?) value for each key instead of building a list.
>>>>>
>>>>> Rationale:
>>>>>
>>>>> While it could be achieved easily enough using Enum.map/2 and
>>>>> Map.new/1, or Enum.into/3, having a function for it could help making the
>>>>> code more explicit about the intent and therefore more readable. Like
>>>>> Enum.group_by/3, I think it is a fairly common operation and it might be
>>>>> a
>>>>> natural candidate for the standard library?
>>>>>
>>>>> Example use case: from a list of Ecto records, create a map of records
>>>>> keyed by `id` for efficient lookups in future code:
>>>>>
>>>>> User |> Repo.all() |> Enum.key_by(fn user -> user.id end)
>>>>>
>>>>> If we want to build a map to lookup user names by their ids:
>>>>> User |> Repo.all() |> Enum.key_by(fn user -> user.id end, fn user ->
>>>>> user.name end)
>>>>>
>>>>>
>>>>> Further considerations:
>>>>>
>>>>> The typical use cases I have in mind would rely on some kind of unique
>>>>> key, so I'm not sure what would be the best API-wise when dealing with
>>>>> duplicate keys and have no real opinion:
>>>>> - keep the last value found for each key
>>>>> - keep the first value found for each key
>>>>> This behaviour could always be changed using `Enum.reverse/1` if
>>>>> needed.
>>>>>
>>>>> What do you think?
>>>>>
>>>>> I have a working branch for this here, happy to open a PR if you are
>>>>> interested:
>>>>> https://github.com/elixir-lang/elixir/compare/master...sabiwara:enum_key_by?expand=1
>>>>>
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