Is there a better way to traverse a tree structure and accumulate leaves than this code?

  def traverse_start(value, acc_list) when is_list(value) do
    for v <- value, reduce: acc_list do
      acc -> acc ++ traverse(v, acc_list)
    end
    |> Enum.uniq()
  end

  def traverse_start(value, acc_list) when is_map(value) do
    for {k, v} <- value, reduce: acc_list do
      acc -> acc ++ traverse([k], v, acc_list)
    end
    |> Enum.uniq()
  end

  def traverse(keys, value, acc_list) when is_map(value) do
    # keys |> IO.inspect
    for {k, v} <- value, reduce: acc_list ++ [keys] do
      acc -> acc ++ traverse(keys ++ [k], v, acc)
    end
  end

  def traverse(keys, value, acc_list) when is_list(value) do
    # keys |> IO.inspect
    for v <- value, reduce: acc_list ++ [keys] do
      acc -> (acc ++ traverse(keys, v, acc)) |> Enum.uniq()
    end
  end

  def traverse(keys, _value, _acc_list) do
    # keys |> IO.inspect
    [keys]
  end

This code traverses a map or list and gets a list of unique paths. It’s used to get column names for a CSV file from an array of JSON documents.

    columns = Report.traverse_start(data_list, []) |> Enum.sort()

input

    data_list = [
      %{},
      %{
        "a" => 1,
        "b" => %{"bb" => 2},
        "c" => %{"cc" => %{"ccc" => 3}},
        "n" => nil,
        "u" => %{"uu" => nil},
        "w" => %{"ww" => %{"www" => nil}},
        "r" => [],
        "z" => %{}
      },
      %{
        "a" => 1,
        "b" => %{"bb" => 2},
        "c" => %{"cc" => %{"ccc" => 3}},
        "n" => nil,
        "u" => %{"uu" => nil},
        "w" => %{"ww" => %{"www" => nil}},
        "r" => [
          %{
            "a" => 1,
            "b" => %{"bb" => 2},
            "c" => %{"cc" => %{"ccc" => 3}},
            "n" => nil,
            "u" => %{"uu" => nil},
            "w" => %{"ww" => %{"www" => nil}},
            "r" => [
              %{
                "a" => 1,
                "b" => %{"bb" => 2},
                "c" => %{"cc" => %{"ccc" => 3}},
                "n" => nil,
                "u" => %{"uu" => nil},
                "w" => %{"ww" => %{"www" => nil}},
                "r" => [],
                "z" => %{}
              },
              %{
                "d" => 4
              }
            ],
            "z" => %{}
          },
          %{
            "d" => 4
          }
        ]
      }
    ]

output

   columns = [
      ["a"],
      ["b"],
      ["b", "bb"],
      ["c"],
      ["c", "cc"],
      ["c", "cc", "ccc"],
      ["n"],
      ["r"],
      ["r", "a"],
      ["r", "b"],
      ["r", "b", "bb"],
      ["r", "c"],
      ["r", "c", "cc"],
      ["r", "c", "cc", "ccc"],
      ["r", "d"],
      ["r", "n"],
      ["r", "r"],
      ["r", "r", "a"],
      ["r", "r", "b"],
      ["r", "r", "b", "bb"],
      ["r", "r", "c"],
      ["r", "r", "c", "cc"],
      ["r", "r", "c", "cc", "ccc"],
      ["r", "r", "d"],
      ["r", "r", "n"],
      ["r", "r", "r"],
      ["r", "r", "u"],
      ["r", "r", "u", "uu"],
      ["r", "r", "w"],
      ["r", "r", "w", "ww"],
      ["r", "r", "w", "ww", "www"],
      ["r", "r", "z"],
      ["r", "u"],
      ["r", "u", "uu"],
      ["r", "w"],
      ["r", "w", "ww"],
      ["r", "w", "ww", "www"],
      ["r", "z"],
      ["u"],
      ["u", "uu"],
      ["w"],
      ["w", "ww"],
      ["w", "ww", "www"],
      ["z"]
    ]