code: def error_rate(y, yhat):
      """Returns the error rate (lower is better).
  
      :param y: true function values
      :param yhat: predicted function values
  
      >>> error_rate([0,0,1,1], [0,0,0,1])
      0.25
  
      """
      return 1.0 - accuracy(y, yhat)
  
imports: import math
  import operator
label_desc: Use image node_id 18 for calling a global function with example usage: error_rate(y, yhat) and returns: unknown