defmodule Rivet.Utils.Math do
  @doc """
  iex> average([])
  0.0
  iex> average([30])
  30.0
  iex> average([30, 32, 20, 18, 23, 26, 27])
  25.142857142857142
  """
  def average([]), do: 0.0

  def average(list),
    do: Enum.sum(list) / length(list)

  @doc """
  iex> stddev([])
  0.0
  iex> stddev([30])
  0.0
  iex> stddev([2, 4, 4, 4, 5, 5, 7, 9])
  2.0
  """
  def stddev(list) do
    mean = average(list)

    variance =
      Enum.map(list, &deviation(&1, mean))
      |> average()

    Float.pow(variance, 0.5)
  end

  def deviation(value, mean), do: Float.pow(value - mean, 2)
end