Add StandardDeviation calculation

BenchmarkDotNet/BenchmarkCompetition.cs

@@ -38,11 +38,13 @@ namespace BenchmarkDotNet
             ConsoleHelper.WriteLineHeader("Competition results:");
             var nameWidth = tasks.Max(task => task.Name.Length) + 1;
             var msWidth = tasks.Max(task => task.Info.Result.MedianMilliseconds.ToString().Length);
+            var stdDevWidth = tasks.Max(task => string.Format("{0:0.00}", task.Info.Result.StandardDeviationMilliseconds).Length);
             foreach (var task in tasks)
-                ConsoleHelper.WriteLineStatistic("{0}: {1}ms [Error: {2:00.00}%]",
+                ConsoleHelper.WriteLineStatistic("{0}: {1}ms [Error = {2:00.00}%, StdDev = {3}]",
                     task.Name.PadRight(nameWidth),
                     task.Info.Result.MedianMilliseconds.ToString().PadLeft(msWidth),
-                    task.Info.Result.Error * 100);
+                    task.Info.Result.Error * 100,
+                    string.Format("{0:0.00}", task.Info.Result.StandardDeviationMilliseconds).PadLeft(stdDevWidth));
         }
     }
 }

BenchmarkDotNet/BenchmarkRunList.cs

@@ -26,18 +26,22 @@ namespace BenchmarkDotNet
 
         public void PrintStatistic()
         {
-            ConsoleHelper.WriteLineStatistic("TickStats: Min={0}, Max={1}, Median={2}, Diff={3:00.00}%",
-                              MinTicks, MaxTicks, MedianTicks, Error * 100);
-            ConsoleHelper.WriteLineStatistic("MsStats: Min={0}, Max={1}, Median={2}",
-                              MinMilliseconds, MaxMilliseconds, MedianMilliseconds);
+            ConsoleHelper.WriteLineStatistic("TickStats: Min={0}, Max={1}, Med={2}, StdDev={3:0}, Err={4:00.00}%",
+                              MinTicks, MaxTicks, MedianTicks, StandardDeviationTicks, Error * 100);
+            ConsoleHelper.WriteLineStatistic("MsStats: Min={0}, Max={1}, Med={2}, StdDev={3:0.00}",
+                              MinMilliseconds, MaxMilliseconds, MedianMilliseconds, StandardDeviationMilliseconds);
         }
 
         public long MinTicks { get { return this.Min(run => run.ElapsedTicks); } }
         public long MaxTicks { get { return this.Max(run => run.ElapsedTicks); } }
         public long MedianTicks { get { return this.Median(run => run.ElapsedTicks); } }
+        public double StandardDeviationTicks { get { return this.StandardDeviation(run => run.ElapsedTicks); } }
+
         public long MinMilliseconds { get { return this.Min(run => run.ElapsedMilliseconds); } }
         public long MaxMilliseconds { get { return this.Max(run => run.ElapsedMilliseconds); } }
         public long MedianMilliseconds { get { return this.Median(run => run.ElapsedMilliseconds); } }
+        public double StandardDeviationMilliseconds { get { return this.StandardDeviation(run => run.ElapsedMilliseconds); } }
+
         public double Error
         {
             get { return (MaxTicks - MinTicks) * 1.0 / MinTicks; }

BenchmarkDotNet/Extensions.cs

@@ -16,5 +16,18 @@ namespace BenchmarkDotNet
                 return list[list.Count / 2];
             return (list[list.Count / 2 - 1] + list[list.Count / 2]) / 2;
         }
+
+        public static double StandardDeviation<TSource>(this IEnumerable<TSource> source, Func<TSource, long> selector)
+        {
+            var list = source.Select(selector).ToList();
+            double result = 0;
+            if (list.Any())
+            {
+                double avg = list.Average();
+                double sum = list.Sum(d => Math.Pow(d - avg, 2));
+                result = Math.Sqrt(sum / list.Count());
+            }
+            return result;
+        }
     }
 }