code: def test_sorting(self):
      sd = idd.MultiData(
          np.arange(4).reshape(2, 2),
          index=["foo", "bar"],
          columns=["f", "g"],
      )
      print(sd)
      sd.sort_index()
  
      print(sd)
      print(sd.loc[:"c"])
  
file_path: qlib/tests/misc/test_index_data.py
imports: import numpy
  import pandas
  import qlib.utils.index_data
  import unittest
label_desc: Use image node_id 3 for calling the IndexDataTest obj's underlying member method code with example usage: obj.test_sorting() without return types