More statistics

lib/benchee.ex

@@ -1,6 +1,8 @@
 defmodule Benchee do
   @default_config %{time: 5}
 
+  alias Benchee.{Statistics, Time}
+
   @doc """
   Returns the initial benchmark suite data structure for Benshee.
   Given an optional map of configuration options, converts seconds in there
@@ -20,7 +22,7 @@ defmodule Benchee do
   @seconds_to_microseconds 1_000_000
   defp convert_time_to_micro_s(config) do
     {_, config} = Map.get_and_update! config, :time, fn(seconds) ->
-      {seconds, seconds * @seconds_to_microseconds}
+      {seconds, Time.seconds_to_microseconds(seconds)}
     end
     config
   end
@@ -58,14 +60,12 @@ defmodule Benchee do
   Creates a report of the benchmark suite run.
   """
   def report(%{jobs: jobs}) do
+
     Enum.map jobs, fn(%{name: name, run_times: times}) ->
-      "#{name} #{Enum.count(times)} #{average(times)}"
+      %{average: average, ips: ips, std_dev: std_dev} = Statistics.statistics(times)
+      "#{name} #{ips} #{average}μs #{std_dev}"
     end
   end
 
-  defp average(series) do
-    total = Enum.sum(series)
-    iterations = Enum.count(series)
-    total / iterations
-  end
+
 end

lib/benchee/statistics.ex

@@ -0,0 +1,35 @@
+defmodule Benchee.Statistics do
+  alias Benchee.Time
+
+  @doc """
+  Calculates statistical data based on a series of run times in microseconds.
+
+  iex> Benchee.Statistics.statistics([200, 400, 400, 400, 500, 500, 700, 900])
+  %{average: 500.0, std_dev: 200.0, ips: 2000.0}
+  """
+  def statistics(run_times) do
+    total_time            = Enum.sum(run_times)
+    iterations            = Enum.count(run_times)
+    average_time          = total_time / iterations
+    iterations_per_second = iterations_per_second(iterations, total_time)
+    standard_deviation    = standard_deviation(run_times, average_time, iterations)
+
+    %{
+      average: average_time,
+      ips:     iterations_per_second,
+      std_dev: standard_deviation
+    }
+  end
+
+  defp iterations_per_second(iterations, time_microseconds) do
+    iterations / (Time.microseconds_to_seconds(time_microseconds))
+  end
+
+  defp standard_deviation(samples, average, iterations) do
+    total_variance = Enum.reduce samples, 0,  fn(sample, total) ->
+      total + :math.pow((sample - average), 2)
+    end
+    variance = total_variance / iterations
+    :math.sqrt variance
+  end
+end

lib/benchee/time.ex

@@ -0,0 +1,11 @@
+defmodule Benchee.Time do
+  @seconds_to_microseconds 1_000_000
+
+  def microseconds_to_seconds(microseconds) do
+    microseconds / @seconds_to_microseconds
+  end
+
+  def seconds_to_microseconds(seconds) do
+    seconds * @seconds_to_microseconds
+  end
+end

test/benchee/statistics_test.exs

@@ -0,0 +1,5 @@
+defmodule Benchee.StatistcsTest do
+  use ExUnit.Case
+  doctest Benchee.Statistics
+
+end