class_docstr: Keeps track of the difference between two data inputs skipping, memorizing
  the last non zero value if the current difference is zero
  
  Formula:
    - diff = data - data1
    - nzd = diff if diff else diff(-1)
class_docstr_tok: ["Keeps","track","of","the","difference","between","two","data","inputs","skipping",",","memorizing","the","last","non","zero","value","if","the","current","difference","is","zero","Formula",":","-","diff","=","data","-","data1","-","nzd","=","diff","if","diff","else","diff","(","-1",")"]
code: def next(self):
      d = self.data0[0] - self.data1[0]
      self.l.nzd[0] = d if d else self.l.nzd[-1]
  
file_path: backtrader/backtrader/indicators/crossover.py
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  from .None import Indicator, And
label_desc: Use image node_id 2 for calling the NonZeroDifference obj's underlying member method code with example usage: obj.next() without return types