Add stddev to rlikestats.rb

bin/rlikestats.rb

@@ -17,6 +17,7 @@
 #  95th Pct.:        2.1000
 #  99th Pct.:        2.1000
 #  Max      :        2.1000
+#  Stddev   :        0.5395
 
 
 class Rlikestats
@@ -28,6 +29,7 @@ def initialize
     self.count = 0
     self.mean  = 0.0
     self.lines = 0
+    self.m2 = 0.0
   end
 
   def run
@@ -39,9 +41,15 @@ def run
       end
       val = line.to_f
       self.count += 1
-      self.mean += (val - mean) / count
+
+      delta = val - mean
+      self.mean = mean + delta / count
+      self.m2 = m2 + delta * (val - mean)
+
       values << val
     end
+    variance = m2 / (count - 1)
+    self.stddev = Math.sqrt(variance)
 
     values.sort!
     print_result
@@ -62,7 +70,11 @@ def print_result
     puts "95th Pct.:  %12.4f" % percentile(0.95)
     puts "99th Pct.:  %12.4f" % percentile(0.99)
     puts "Max      :  %12.4f" % values.last
+    puts "Stddev   :  %12.4f" % stddev
   end
+
+  private
+  attr_accessor :m2, :stddev
 end
 
 Rlikestats.new.run