Untitled notebook

Mix.install([{:benchee, "~> 1.1"}, {:extrace, "~> 0.5.0"}])

Section

defmodule Uniq do
  @a [
    %{id: 1},
    %{location: 2, user: %{id: 1}},
    %{location: 3, user: %{id: 1}},
    %{location: 2, user: %{id: 2}},
    %{location: 3, user: %{id: 3}},
    %{location: 3, user: %{id: nil}}
  ]
  def map_filter_uniq do
    @a
    |> Enum.map(&Map.get(&1, :user))
    |> Enum.map(fn
      nil -> nil
      x -> Map.get(x, :id)
    end)
    |> Enum.filter(& &1)
    |> Enum.uniq()
  end

  def for_uniq do
    for %{user: %{id: id}} <- @a, is_integer(id), uniq: true, do: id
  end

  def user(:get, user, next) do
    Enum.map(user, next)
  end

  def get_in_filter_uniq do
    @a
    |> get_in([&amp;user/3, :user, :id])
    |> Enum.filter(&amp; &amp;1)
    |> Enum.uniq()
  end

  def reduce do
    Enum.reduce(@a, {[], %{}}, fn
      %{user: %{id: id}}, {_uniq, set} = acc when is_map_key(set, id) -> acc
      %{user: %{id: id}}, {uniq, set} when is_integer(id) -> {[id | uniq], Map.put(set, id, true)}
      _no_user_id_found, acc -> acc
    end)
    |> elem(0)
  end
end

Benchee.run(%{
  "for_uniq" => &Uniq.for_uniq/0,
  "get_in_filter_uniq" => &Uniq.get_in_filter_uniq/0,
  "map_filter_uniq" => &Uniq.map_filter_uniq/0,
  "reduce" => &Uniq.reduce/0
})

Extrace.calls({Uniq, :_, :return_trace}, 100, scope: :local)
[Uniq.reduce(), Uniq.for_uniq(), Uniq.get_in_filter_uniq(), Uniq.map_filter_uniq()]