gistfile1.txt

I have a challenge of transforming the data from 1 state to another. I have written my implementation, but I know it could be done, just could’t figure it out. I was looking into using Streams, but struggling to implement it. Any suggestions?

input = [["foo", 56, "0", "1"],
         ["bar", 34, "2", "3"],
         ["bla", 90, "2", "1"],
         ["hey", 10, "4", "1"]]

output = [%{"0" => [56]},
          %{"2" => [90, 34]},
          %{"4" => [10]}
         ]

input
  |> Enum.group_by(fn([_col1, _col2, col3, _col4]) -> col3 end)
  |> Enum.map(&extract_col_2_values/1)

defp extract_col_2_values({col3, data}) do
  col2_values_sorted_by_col4 =
    data
    |> Enum.sort_by(fn ([_col1, _col2, _col3, col4]) ->
                      String.to_integer(col4)
                    end)
  %{col3 => Enum.map(col2_values_sorted_by_col4, fn([_col1, col2, _col3, _col4]) -> col2 end) }
end

input
|> Enum.map(fn [_, col2, col3, col4] -> {col3, String.to_integer(col4), col2} end)
|> Enum.sort()
|> Enum.chunk_by(&elem(&1, 0))
|> Enum.map(fn entries ->
  {key, _, _} = hd(entries)
  %{key => Enum.map(entries, &elem(&1, 2))}
end)