class_docstr: Rate of change filter as described in http://stockcharts.com/school/doku.php?id=chart_school:technical_indicators:rate_of_change_roc_and_momentum.
  
  :param dataSeries: The DataSeries instance being filtered.
  :type dataSeries: :class:`pyalgotrade.dataseries.DataSeries`.
  :param valuesAgo: The number of values back that a given value will compare to. Must be > 0.
  :type valuesAgo: int.
  :param maxLen: The maximum number of values to hold.
      Once a bounded length is full, when new items are added, a corresponding number of items are discarded from the
      opposite end. If None then dataseries.DEFAULT_MAX_LEN is used.
  :type maxLen: int.
code: def __init__(self, dataSeries, valuesAgo, maxLen=None):
      assert valuesAgo > 0
      super(RateOfChange, self).__init__(
          dataSeries, ROCEventWindow(valuesAgo + 1), maxLen
      )
  
file_path: pyalgotrade/pyalgotrade/technical/roc.py
imports: from pyalgotrade import technical
label_desc: Use image node_id 1 to create a new RateOfChange object from inherited base classes: technical with example: obj = RateOfChange(dataSeries, valuesAgo, maxLen)