code: def test_groupby_nth_interval():
      # GH#24205
      idx_result = MultiIndex(
          [
              pd.CategoricalIndex(
                  [pd.Interval(0, 1), pd.Interval(1, 2)]
              ),
              pd.CategoricalIndex(
                  [pd.Interval(0, 10), pd.Interval(10, 20)]
              ),
          ],
          [[0, 0, 0, 1, 1], [0, 1, 1, 0, -1]],
      )
      df_result = DataFrame(
          {"col": range(len(idx_result))}, index=idx_result
      )
      result = df_result.groupby(level=[0, 1], observed=False).nth(0)
      val_expected = [0, 1, 3]
      idx_expected = MultiIndex(
          [
              pd.CategoricalIndex(
                  [pd.Interval(0, 1), pd.Interval(1, 2)]
              ),
              pd.CategoricalIndex(
                  [pd.Interval(0, 10), pd.Interval(10, 20)]
              ),
          ],
          [[0, 0, 1], [0, 1, 0]],
      )
      expected = DataFrame(
          val_expected, index=idx_expected, columns=["col"]
      )
      tm.assert_frame_equal(result, expected)
  
imports: import numpy
  import pytest
  import pandas
  from pandas import DataFrame, Index, MultiIndex, Series, Timestamp, isna
  import pandas._testing
label_desc: Use image node_id 37 for calling a global function with example usage: test_groupby_nth_interval() without return types