elixir implementation of array combination: http://ruby-doc.org/core-1.9.3/Array.html#method-i-combination

array_combination.ex

defmodule MyModule.ArrayCombination do

  def combination(_, 0), do: [[]]
  def combination(list, n) when (length(list) < n), do: []
  def combination(list, n) when (length(list) == n), do: [list]
  def combination(list, 1), do: Enum.map(list, fn(x)-> [x] end)
  def combination([head|tail], n) do
    Enum.map(combination(tail, n-1), fn(x)-> [head|x] end) ++ combination(tail, n)
  end

end