Iterating a list to compare all elements with each other

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You can do the same with recursion:

list = [1, 2, 3, 4]

defmodule Rec do
  def compare(list, acc \\ [])

  def compare([_], acc) do
    acc
    |> Enum.reverse()
    |> List.flatten()
  end

  def compare([cur | rest], acc) do
    compare(rest, [Enum.map(rest, &{cur, &1}) | acc])
  end
end

Rec.compare(list)
# [{1, 2}, {1, 3}, {1, 4}, {2, 3}, {2, 4}, {3, 4}]

And you can look at combinatorics: GitHub - tallakt/comb: Elixir combinatorics - permutations and combinations of lists

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