code: def update_x_axis_index(self):
      SignalsFileBase.update_x_axis_index(self)
  
      # update the x axis for the bollinger bands
      for signal in self.signals.values():
          if signal.has_bollinger_bands:
              signal.set_bands_source()
  
file_path: coach/rl_coach/dashboard_components/signals_files_group.py
imports: import os
  from multiprocessing import Process, Manager
  from os.path import basename
  import pandas
  from rl_coach.dashboard_components.globals import x_axis_options, add_directory_csv_files, show_spinner, x_axis
  from rl_coach.dashboard_components.signals_file_base import SignalsFileBase
  from rl_coach.dashboard_components.signals_file import SignalsFile
label_desc: Use image node_id 4 for calling the SignalsFilesGroup obj's underlying member method code with example usage: obj.update_x_axis_index() without return types