class_docstr: Stack plotted objects on top of each other
  
  The objects to stack are those that have
  an overlapping x range.
  
  Parameters
  ----------
  vjust :
      By what fraction to avoid overlapping the lower object,
      where `0` gives a complete overlap and `1` gives no overlap.
  reverse :
      Reverse the order of the stacked groups if true.
docstr: Verify, modify & return a copy of the params.
docstr_tok: ["Verify",",","modify","&","return","a","copy","of","the","params","."]
code: def setup_params(self, data):
      """
      Verify, modify & return a copy of the params.
      """
      # Variable for which to do the stacking
      if "ymax" in data:
          if any((data["ymin"] != 0) & (data["ymax"] != 0)):
              warn(
                  "Stacking not well defined when not "
                  "anchored on the axis.",
                  PlotnineWarning,
              )
          var = "ymax"
      elif "y" in data:
          var = "y"
      else:
          warn(
              "Stacking requires either ymin & ymax or y "
              "aesthetics. Maybe you want position = 'identity'?",
              PlotnineWarning,
          )
          var = None
  
      params = self.params.copy()
      params["var"] = var
      params["fill"] = self.fill
      return params
  
file_path: plotnine/plotnine/positions/position_stack.py
imports: from __future__ import annotations
  from warnings import warn
  import numpy
  import pandas
  from .._utils import remove_missing
  from ..exceptions import PlotnineWarning
  from .position import position
label_desc: Use image node_id 2 for calling the position_stack obj's underlying member method code with example usage: obj.setup_params(data) and returns: params