code: def _headers_single_series(
      df: pd.DataFrame, mapping: pd.Series
  ) -> tuple:
      """
      Extract headers and values for a single level.
      Applies to `.value` for a single level extract,
      or where names_pattern is a sequence.
      """
      # get positions of columns,
      # to ensure interleaving is possible
      # so if we have a dataframe like below:
      #        id  x1  x2  y1  y2
      #    0   1   4   5   7  10
      #    1   2   5   6   8  11
      #    2   3   6   7   9  12
      # then x1 will pair with y1, and x2 will pair with y2
      # if the dataframe column positions were alternated, like below:
      #        id  x2  x1  y1  y2
      #    0   1   5   4   7  10
      #    1   2   6   5   8  11
      #    2   3   7   6   9  12
      # then x2 will pair with y1 and x1 will pair with y2
      # it is simply a first come first serve approach
      outcome = mapping.groupby(mapping, sort=False, observed=True)
      group_size = outcome.size()
      group_max = group_size.max()
      # the number of groups should be the same;
      # if not, build a MultiIndex and reindex
      # to get equal numbers for each label
      if group_size.nunique() > 1:
          positions = outcome.cumcount()
          df.columns = [mapping, positions]
          indexer = group_size.index, np.arange(group_max)
          indexer = pd.MultiIndex.from_product(indexer)
          df = df.reindex(columns=indexer, copy=False)
          df.columns = df.columns.get_level_values(0)
      else:
          df.columns = mapping
      outcome = _dict_from_grouped_names(df=df)
      return outcome, group_max
  
imports: import re
  import warnings
  from collections import defaultdict
  from itertools import chain, zip_longest
  from typing import Callable, Optional, Pattern, Union
  import numpy
  import pandas
  import pandas_flavor
  from pandas.api.types import is_categorical_dtype, is_extension_array_dtype, is_list_like
  from pandas.core.dtypes.concat import concat_compat
  from janitor.functions.utils import _computations_expand_grid, get_index_labels
  from janitor.utils import check, refactored_function
label_desc: Use image node_id 9 for calling a global function with example usage: _headers_single_series(df, mapping) and returns: outcome,  group_max