This is correct. map |> Enum.map(&fun) |> Map.new is the fastest possible
way to take a map and iterate over all of its keys.
Reason being, building a new list of {k, v} pairs and calling the
`:maps.from_list` NIF always beats out N Map.put calls, which is how into:
%{} works. It also creates less garbage. Map.new is basically just
:maps.from_list if it gets passed a list.
On Thursday, July 7, 2016 at 2:48:39 PM UTC-4, Michał Muskała wrote:
>
> What do you mean by not converting to a list?
> The fastest way right now of doing a map on a map is actually to convert
> to list, map and convert back to a map.
> I’d suspect that’s the case with a lot of data structures as well,
> actually. Lists are simply really good for recursion.
> The benefit is even greater if you do multiple operations on those lists,
> as the conversion happens (ideally) only
> once.
>
> Michał.
>
> On 07 Jul 2016, at 19:35, Peter Hamilton <petergh...@gmail.com
> <javascript:>> wrote:
>
> Does the Enumerable protocol enable the performance improvement of not
> converting to a list? I don't think it does.
>
> On Thu, Jul 7, 2016, 10:24 AM Andrea Leopardi <an.le...@gmail.com
> <javascript:>> wrote:
>
>> Enum.into/3 should do what you want :)
>>
>> On Thursday, 7 July 2016, Wiebe-Marten Wijnja <w.m.w...@panache-it.com
>> <javascript:>> wrote:
>>
>>> I propose to add `into: collectable` as optional third argument to
>>> Enum.map.
>>>
>>> This would allow mapping over things without first converting it to a
>>> list and then convert it back.
>>>
>>> So:
>>>
>>> %{"a" => 1, "b" => 2}
>>> |> Enum.map(fn {k, v} -> {String.upcase(k), v} end)
>>> |> Enum.into(%{})
>>>
>>> could be written as:
>>>
>>> %{"a" => 1, "b" => 2}
>>> |> Enum.map(fn {k, v} -> {String.upcase(k), v} end, into: %{})
>>>
>>> Not having to do the list conversion in the middle might also improve
>>> performance.
>>>
>>>
>>> Right now, enumerating and collecting in one go is of course possible
>>> using `Kernel.SpecialForms.for`. `for` is however not very
>>> pipeline-friendly.
>>>
>>>
>>> What do you think?
>>>
>>>
>>> Sincerely,
>>>
>>> ~Wiebe-Marten
>>>
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>> Andrea Leopardi
>> an.le...@gmail.com <javascript:>
>>
>>
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