The stream version is by far the slowest, which isn't surprising since
streams bring some overhead. Didn't measure memory usage though
https://gist.github.com/joladev/2b51260107078a1fc7f9d4504916fe21
Honestly, I tend to agree it would be nice to add it, for feature
completeness, even if it doesn't improve performance hugely. I understand
the desire to avoid unnecessary clutter in the core language, but this is a
core erlang function that we're explicitly not wrapping, when most of the
other ones are wrapped. And most likely just because it wasn't around from
the start. It's quite a bit more ergonomic to use `Map.filter` rather than
`for` or `map|>Enum.filter(pred)|>Enum.into({})`. Much cleaner.
Not too hard to implement your own version of `Map.filter` though, so I
don't feel too strongly about it.
On Thu, Aug 15, 2019 at 11:12 AM Alexei Sholik <alcosho...@gmail.com> wrote:
> The simplest alternative is to use :maps.filter(). It's not as easy to
> pipe into, but that's a minor concern for me.
>
> As another alternative, this should be faster and have lower memory
> footprint than using Enum, although you'd need to benchmark it as well to
> be sure:
>
> map
> |> Stream.filter(predicate)
> |> Map.new()
>
> Personally, I would love to see an extension for Map.new() that would
> allow filtering the first argument in addition to the currently supported
> transformation. So instead of the current
>
> Map.new(enumerable, fn thing -> {key, val} end)
>
> we could have
>
> Map.new(enumerable, map: fn thing -> {key, val} end, filter: fn {_key,
> val} -> predicate(val) end)
>
> Such an extension is unlikely to be added though because it would be
> another way of doing what is already possible with Enum, Stream, and Map.
>
> On Thu, Aug 15, 2019 at 10:29 AM Roman Smirnov <pom...@gmail.com> wrote:
>
>> Since OTP 18 there is a pretty convenient function :maps.filter
>> <http://erlang.org/doc/man/maps.html#filter-2>.
>>
>> I think it would be nice to have Map.filter(map, predicate) in Elixir as
>> well instead of doing
>>
>>
>> map|> Enum.filter(predicate)|> Enum.into(%{})
>>
>>
>> or
>>
>> for {key, value} <- map, some_filter(key, value), into: %{}, do: {key, value}
>>
>> The first one alternative is slower, b/c of 2-step transformation, and
>> the second one consume more memory, could not be piped and has a lack
>> of expressiveness (too imperative way to do a simple filtration).
>> There were benchmarks and a small discussion in PR:
>> https://github.com/elixir-lang/elixir/pull/9292, but the discussion
>> should be moved to this mailing list.
>>
>>
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