docstr: Called by DataCollection objects when Preprocessors
  are appended.
docstr_tok: ["Called","by","DataCollection","objects","when","Preprocessors","are","appended","."]
code: def initialize(self, data_collection):
      """Called by DataCollection objects when Preprocessors
      are appended.
      """
  
      if self.data_groups is None:
          self.data_groups = data_collection.data_groups
      else:
          self.data_groups = {
              label: data_group
              for label, data_group in list(
                  data_collection.data_groups.items()
              )
              if label in self.data_groups
          }
  
      self.data_groups_iterator = list(self.data_groups.items())
  
      return
  
imports: import os
  import numpy
  from deepneuro.utilities.util import add_parameter, replace_suffix, cli_sanitize, docker_print
  from deepneuro.utilities.conversion import read_image_files, save_data
label_desc: Use image node_id 12 for calling the Preprocessor obj's underlying member method code with example usage: obj.initialize(data_collection) without return types