the code is here
def f() do
File.read!("15821.csv")
|> String.split("\r", trim: true)
|> Enum.map(fn x -> String.split(x, ",") end)
|> Enum.group_by(fn x -> Enum.at(x, 0) end)
end
the csv file is here: https://github.com/cjen07/groupby_question/blob/master/15821.csv
there are four keys in output, but you cannot identify why by just inspecting in iex
I think the invisible character comes from the headline of the csv file, but why is it permitted in elixir?