code: def add_string_index_col(dataset):
      """Add an index column of type string instead of numeric to the dataset.
  
      :param dataset: Dataset to add the index column of type string to.
      :type dataset: pandas.DataFrame
      """
      dataset = dataset.reset_index()
      dataset[STRING_INDEX] = dataset["index"].astype("string")
      dataset.drop(columns=["index"], inplace=True)
      return dataset
  
imports: import re
  import time
  from enum import Enum
  import numpy
  import pandas
  import pytest
  from common_utils import replicate_dataset
  from erroranalysis._internal.cohort_filter import filter_from_cohort
  from erroranalysis._internal.constants import ARG, COLUMN, COMPOSITE_FILTERS, DIFF, LEAF_INDEX, METHOD, OPERATION, PRED_Y, ROW_INDEX, SPLIT_FEATURE, SPLIT_INDEX, TRUE_Y, CohortFilterMethods, CohortFilterOps, Metrics, ModelTask, regression_metrics
  from erroranalysis._internal.error_analyzer import ModelAnalyzer, PredictionsAnalyzer
  from erroranalysis._internal.surrogate_error_tree import TreeSide, cache_subtree_features, compute_error_tree, create_surrogate_model, get_categorical_info, get_max_split_index, traverse
  from rai_test_utils.datasets.tabular import create_adult_census_data, create_binary_classification_dataset, create_cancer_data, create_diabetes_data, create_iris_data, create_simple_titanic_data
  from rai_test_utils.models.model_utils import create_models_classification
  from rai_test_utils.models.sklearn import create_kneighbors_classifier, create_sklearn_random_forest_regressor, create_titanic_pipeline
  from raiutils.exceptions import UserConfigValidationException
label_desc: Use image node_id 4 for calling a global function with example usage: add_string_index_col(dataset) and returns: dataset