class_docstr: Running statistics for elements in a stream
  
  Can take single values or iterables
  
  1. Implements Welford's algorithm for computing a running mean
  and standard deviation
  2. Min-Heap to find top-k where k < capacity (kwarg)
  Methods:
      mean    - returns the mean
      std     - returns the std
      meanfull- returns the mean and std of the mean
      topk(k) - returns the kth highest value for k < capacity
code: def std(self) -> float:
      if self.k == 1:
          return 0
      return math.sqrt(self.sum_squares / (self.k - 1))
  
file_path: ReAgent/reagent/core/running_stats.py
imports: import math
label_desc: Use image node_id 7 for calling the RunningStats obj's underlying member method code with example usage: obj.std() and returns: math, int