Problem Statement

Write a stateful function, class, generator or co-routine that takes a series of floating point numbers, one at a time, and returns the running standard deviation of the series. The task implementation should use the most natural programming style of those listed for the function in the implementation language; the task must state which is being used. Do not apply Bessel's correction; the returned standard deviation should always be computed as if the sample seen so far is the entire population.

Use this to compute the standard deviation of this demonstration set,

{ 2 , 4 , 4 , 4 , 5 , 5 , 7 , 9 }

{\displaystyle {2,4,4,4,5,5,7,9}}

, which is

2

{\displaystyle 2}

.

Let's start with the solution:

T SD
   sum = 0.0
   sum2 = 0.0
   n = 0.0

   F ()(x)
      .sum += x
      .sum2 += x ^ 2
      .n += 1.0
      R sqrt(.sum2 / .n - (.sum / .n) ^ 2)

V sd_inst = SD()
L(value) [2, 4, 4, 4, 5, 5, 7, 9]
   print(value‘ ’sd_inst(value))