code/breadcrumb/analysis/tools.py

   1 import math
   2
   3 def standard_deviation(seq, mu):
   4     """Returns the standard deviation of a given sequence."""
   5     for x in seq:
   6         s_sq = s_sq + (x - mu)**2
   7         s_cm = s_cm + (x - mu)
   8
   9     var = (s_sq - (s_cm**2)/len(seq))/(len(seq) - 1)
  10     return math.sqrt(var)
  11
  12 def z_scores(seq, mu, sigma):
  13     """
  14     Returns an list of Z-scores (standard deviations from the mean).
  15
  16     Given a sequence of floats, a mean value (mu) and a standard deviation
  17     (sigma), this returns a list of equal length as the input sequence.
  18
  19     The input sequence must be 1D.
  20     """
  21     return [float((value - mu)/sigma) for value in seq]
  22