code: def _get_comparators(
      self, mf: MetricFrame, comparator: str, method: str
  ):
      if comparator == "difference":
          actual = mf.difference_ci(method=method)
          nominal = mf.difference(method=method)
          tol = ABS_TOL
      elif comparator == "ratio":
          actual = mf.ratio_ci(method=method)
          nominal = mf.ratio(method=method)
          tol = 2 * ABS_TOL  # Ratios tend to be poorly behaved
      else:
          raise ValueError(f"Unrecognised option: {comparator}")
  
      return actual, nominal, tol
  
imports: import numpy
  import pytest
  import sklearn.metrics
  from fairlearn.metrics import MetricFrame, count
  from .data_for_test import g_1, g_2, y_p, y_t
label_desc: Use image node_id 1 for calling the TestGroupComparisons obj's underlying member method code with example usage: obj._get_comparators(mf, comparator, method) and returns: actual,  nominal,  tol