Data commit

Task/Cumulative-standard-deviation/Icon/cumulative-standard-deviation.icon

@@ -0,0 +1,22 @@
+procedure main()
+
+stddev() # reset state / empty
+every  s := stddev(![2,4,4,4,5,5,7,9]) do
+   write("stddev (so far) := ",s)
+
+end
+
+procedure stddev(x)  # running standard deviation
+static X,sumX,sum2X
+
+   if /x then {   # reset state
+      X := []
+      sumX := sum2X := 0.
+      }
+   else {         # accumulate
+      put(X,x)
+      sumX +:= x
+      sum2X +:= x^2
+      return sqrt( (sum2X / *X) - (sumX / *X)^2 )
+      }
+end