Budget.ex

defmodule Budget do
 def sub_totals(expenses) do
   allCategories =
     Enum.uniq for %{type: t, cost: _} <- expenses, do: t
   category_costs = Enum.map(allCategories, fn(x) -> category_total(expenses, x) end)
 end

  def category_total(expenses, category) do
    catExpenses =
      Enum.sum for %{type: ^category, cost: c} <- expenses, do: c
    %{category: category, total: catExpenses}
  end
end