# Convert this python code into elixir

**URL:** <https://forum.elixirforum.com/t/convert-this-python-code-into-elixir/21834>\
**Category:** Questions\
**Tags:** list-comprehension\
**Created:** [April 23, 2019, 12:09am UTC](https://forum.elixirforum.com/t/convert-this-python-code-into-elixir/21834 "2019-04-23T00:09:43Z")\
**Posts on this page:** 1\
**Showing post:** 2

<div class="post-metadata">

**Author:** ![Eiji](https://forum.elixirforum.com/user_avatar/forum.elixirforum.com/eiji/32/36743_2.png) [@Eiji](https://forum.elixirforum.com/u/Eiji)\
**Post date:** [April 23, 2019, 1:33am UTC](https://forum.elixirforum.com/t/convert-this-python-code-into-elixir/21834/2 "2019-04-23T01:33:04Z")

</div>

How about this one:

```elixir
defmodule Example do
  @spec sample(list(), list(), non_neg_integer()) :: list()
  # ensures that parameters are in correct types
  # calculates evenly spacing
  def sample(first, second, rotation \\ 0)
      when is_list(first) and is_list(second) and is_integer(rotation) and rotation >= 0 do
    first_length = length(first)
    second_length = length(second)

    if first_length > second_length do
      every = div(first_length, second_length)
      do_sample(first, second, every, rotation)
    else
      every = div(second_length, first_length)
      do_sample(second, first, every, rotation)
    end
  end

  # make sure that rotation does not conflicts with evenly spacing
  defp do_sample(first, second, every, rotation) when rotation > every do
    corrected_rotation = rem(rotation, every)
    do_sample(first, second, every, corrected_rotation)
  end

  # for each indexed element
  # in reversed order (important for inserting index conflicts)
  # call custom insert with index calculated by index of second list, every and rotation
  defp do_sample(first, second, every, rotation) do
    second
    |> Enum.with_index()
    |> Enum.reverse()
    |> Enum.reduce(first, &custom_insert(&1, &2, every, rotation))
  end

  # small pattern-matching optimization
  defp custom_insert({element, 0}, acc, _every, rotation),
    do: List.insert_at(acc, rotation, element)

  # small pattern-matching optimization
  defp custom_insert({element, 1}, acc, every, rotation),
    do: List.insert_at(acc, every + rotation, element)

  defp custom_insert({element, index}, acc, every, rotation),
    do: List.insert_at(acc, every * index + rotation, element)
end

a = Enum.to_list(1..4) # range to list: [1, 2, 3, 4]
b = String.graphemes("ab") # string to grapheme list: ["a", "b"]
Example.sample(a, b) # ["a", 1, 2, "b", 3, 4]
Example.sample(a, b, 0) # ["a", 1, 2, "b", 3, 4]
Example.sample(a, b, 1) # [1, "a", 2, 3, "b", 4]
Example.sample(a, b, 2) # [1, 2, "a", 3, 4, "b"]
Example.sample(a, b, 3) # [1, "a", 2, 3, "b", 4]
Example.sample(a, b, 4) # ["a", 1, 2, "b", 3, 4]
Example.sample(a, b, 5) # [1, "a", 2, 3, "b", 4]

```

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