docstr: A proxy-call to the dataframe's `.nunique()`.
code: def nunique(self):
      """
      A proxy-call to the dataframe's `.nunique()`.
      """
      return self.dataframe.nunique()
  
imports: from abc import ABC
label_desc: Use image node_id 36 for calling the DataframeAbstract obj's underlying member method code with example usage: obj.nunique() and returns: self