Elixir理解效率

Question

我有一个大型数据集，我正在执行以下操作：

data = %{
  city: ["Chiselhurst", "Saskatchewan", "Boston"],
  day: [1, 2, 3, 4, 5, 6, 7],
  transportation: ["plane", "train", "automobile"]
}

defmodule Make do
  def combos(data) do
    for city <- data[:city],
        day <- data[:day],
        transportation <- data[:transportation] do
          List.flatten([city, day, transportation])
        end
  end

  def filter_map(data) do
    data
    |> Enum.filter_map(fn(x) -> x[:day] > 5 end, &(%{:trip => &1}))
  end

  def combos_filter(data) do
    data
    |> combos
    |> filter_map
  end
end

有没有办法让理解（Make.combos）更有效率？

有没有办法异步过滤？我一直在使用Task.async / Task.await，但我们无法将其与Enum.filter一起使用。

更新

day_range = for n <- 1..5_000_000, do: n

data = %{
  city: ["Chiselhurst", "Saskatchewan", "Boston"],
  day: day_range,
  transportation: ["plane", "train", "automobile"]
}


defmodule Make do
  def combos(data) do
    for city <- data[:city],
        day <- data[:day],
        transportation <- data[:transportation] do
          [city, day, transportation]
        end
  end

  def combos_async(data) do
    chiselhurst = Task.async(fn -> partial_combos("Chiselhurst", data) end)
    saskatchewan = Task.async(fn -> partial_combos("Saskatchewan", data) end)
    boston = Task.async( fn -> partial_combos("Boston", data) end)

    Task.await(chiselhurst, 1000000) ++ Task.await(saskatchewan, 1000000) ++ Task.await(boston, 1000000)

  end

  defp partial_combos(city, data) do
    for day <- data[:day],
        transportation <- data[:transportation] do
          [city, day, transportation]
        end
  end

end