Of course some numbers would be great to look at here - here is a benchmark
for an implementation of Map.split_with/2 comparing the results agains a
few implementations using the current standard library
Code
```elixir
defmodule SplitWith do
def test do
map = Map.new(0..1000, fn n -> {n, n} end)
predicate = fn {x, _} -> rem(x, 2) == 0 end
Benchee.run(%{
"split_with" => fn -> split_with(map, predicate) end,
"enum_split_with" => fn -> enum_split_with(map, predicate) end,
"enum_reduce" => fn -> enum_reduce(map, predicate) end,
"map_filter_reject" => fn -> map_filter_reject(map, predicate) end
})
end
def split_with(map, fun) when is_map(map) and is_function(fun, 1) do
iter = :maps.iterator(map)
next = :maps.next(iter)
{while_true, while_false} = do_split_with({[], []}, next, fun)
{:maps.from_list(while_true), :maps.from_list(while_false)}
end
defp do_split_with(acc, :none, _fun), do: acc
defp do_split_with({while_true, while_false}, {key, value, iter}, fun) do
if fun.({key, value}) do
do_split_with({[{key, value} | while_true], while_false},
:maps.next(iter), fun)
else
do_split_with({while_true, [{key, value} | while_false]},
:maps.next(iter), fun)
end
end
def map_filter_reject(map, predicate) do
{Map.filter(map, &predicate.(&1)), Map.filter(map, fn pair -> not
predicate.(pair) end)}
end
def enum_reduce(map, predicate) do
Enum.reduce(map, {%{}, %{}}, fn {key, value} = pair, {while_true,
while_false} ->
if predicate.(pair) do
{Map.put(while_true, key, value), while_false}
else
{while_true, Map.put(while_false, key, value)}
end
end)
end
def enum_split_with(map, predicate) do
{while_true, while_false} = Enum.split_with(map, &predicate.(&1))
{Map.new(while_true), Map.new(while_false)}
end
end
```
Benchee results
```
iex(1)> SplitWith.test
Operating System: macOS
CPU Information: Intel(R) Core(TM) i9-9980HK CPU @ 2.40GHz
Number of Available Cores: 16
Available memory: 32 GB
Elixir 1.13.0
Erlang 24.0.5
Benchmark suite executing with the following configuration:
warmup: 2 s
time: 5 s
memory time: 0 ns
parallel: 1
inputs: none specified
Estimated total run time: 28 s
Benchmarking enum_reduce...
Benchmarking enum_split_with...
Benchmarking map_filter_reject...
Benchmarking split_with...
Name ips average deviation median
99th %
split_with 5.73 K 174.41 μs ±10.32% 170 μs
243 μs
enum_split_with 5.06 K 197.47 μs ±12.64% 191 μs
291 μs
enum_reduce 4.52 K 221.10 μs ±22.96% 207 μs
435 μs
map_filter_reject 4.52 K 221.15 μs ±11.35% 215 μs
313 μs
Comparison:
split_with 5.73 K
enum_split_with 5.06 K - 1.13x slower +23.06 μs
enum_reduce 4.52 K - 1.27x slower +46.69 μs
map_filter_reject 4.52 K - 1.27x slower +46.73 μs
```
So we do get some modest gains with the new implementation. Let me know
what your thoughts are on moving forward!
And as always - really appreciate your work!
On Monday, December 13, 2021 at 12:51:30 PM UTC-6 José Valim wrote:
> Hi Chris,
>
> Thanks for the proposal.
>
> I would like to first see benchmarks that show a Map implementation can be
> considerably more efficient. Otherwise, if it is about saving a couple
> Map.new calls, then I would rather not add it, as it will move to copying
> many more functions from Enum to Map.
>
> On Mon, Dec 13, 2021 at 7:42 PM Chris Miller <camil...@gmail.com> wrote:
>
>> Is there any interest in adding a `Map.split_with/2` that would take a
>> function of `{key :: any(), value :: any()} -> boolean` and returns
>> `{map_where_true :: map(), map_where_false :: map()}`?
>>
>> I know this functionality can be created easily with the functionality
>> thats already exposed, but it seems like it might be a nice addition and
>> would add greater parity between Enum and Map - it could also be added to
>> Keyword, even thought the distinction between Keyword.split_with and
>> Enum.split_with would be nominal.
>>
>>
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>>
>
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