This doesn’t even work, as you discard the map that you put into. Therefore the last map will still be %{}.

You can also nest comprehensions. For example:

list = Enum.to_list(1..9)
list_of_lists = Enum.chunk_every(list, 3)
IO.puts("#{inspect(list_of_lists, [charlists: :as_lists])}")
fun = &(&1*&1)
result =
  for {row,index} <- Enum.with_index(list_of_lists), into: %{}, do:
    {index, (
      for element <- row, into: %{}, do: {element, fun.(element)}
    )}
IO.puts("#{inspect(result)}")

iex(1)> list = Enum.to_list(1..9)
[1, 2, 3, 4, 5, 6, 7, 8, 9]
iex(2)> list_of_lists = Enum.chunk_every(list, 3)
[[1, 2, 3], [4, 5, 6], '\a\b\t']
iex(3)> IO.puts("#{inspect(list_of_lists, [charlists: :as_lists])}")
[[1, 2, 3], [4, 5, 6], [7, 8, 9]]
:ok
iex(4)> fun = &(&1*&1)
#Function<6.127694169/1 in :erl_eval.expr/5>
iex(5)> result =
...(5)>   for {row,index} <- Enum.with_index(list_of_lists), into: %{}, do:
...(5)>     {index, (
...(5)>       for element <- row, into: %{}, do: {element, fun.(element)}
...(5)>     )}
%{
  0 => %{1 => 1, 2 => 4, 3 => 9},
  1 => %{4 => 16, 5 => 25, 6 => 36},
  2 => %{7 => 49, 8 => 64, 9 => 81}
}
iex(6)> IO.puts("#{inspect(result)}")
%{0 => %{1 => 1, 2 => 4, 3 => 9}, 1 => %{4 => 16, 5 => 25, 6 => 36}, 2 => %{7 => 49, 8 => 64, 9 => 81}}
:ok
iex(7)>

… keeping in mind that for is a comprehension expression, not a for (loop) statement. As a rule you do not use comprehensions for side effects like “printing data” but for data transformation into a Collectable (a list by default).

I have the feeling that these statements contradict each other.

Also, I’m pretty sure that you are not dealing with arrays at all but nested lists.

Then we do not have “loops” in elixir, we have comprehensions, and you should be able to nest them of course…

Still, it’s as @aseigoalready said, without knowing more about your input and your expected output it is hard to tell what’s the best way to solve the problem.

Perhaps you can tell more about the original problem, then only asking about a way to solve it?