lib: add standard derivation computation to counter

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>

diff --git a/lib/counter.nit b/lib/counter.nit
index 4c7b6d6..1c2b9ed 100644 (file)
--- a/lib/counter.nit
+++ b/lib/counter.nit
@@ -162,6 +162,16 @@ class Counter[E: Object]
                end
                return sum.to_f / values.length.to_f
        end
+
+       # The standard derivation of the counter values
+       fun std_dev: Float do
+               var avg = self.avg
+               var sum = 0.0
+               for value in map.values do
+                       sum += (value.to_f - avg).pow(2.0)
+               end
+               return (sum / map.length.to_f).sqrt
+       end
 end
 
 private class CounterSorter[E: Object]