code: def test_apply_iteration():
      # #2300
      N = 1000
      ind = date_range(start="2000-01-01", freq="D", periods=N)
      df = DataFrame({"open": 1, "close": 2}, index=ind)
      tg = Grouper(freq="ME")
  
      grouper, _ = tg._get_grouper(df)
  
      # Errors
      grouped = df.groupby(grouper, group_keys=False)
  
      def f(df):
          return df["close"] / df["open"]
  
      # it works!
      result = grouped.apply(f)
      tm.assert_index_equal(result.index, df.index)
  
imports: from datetime import datetime
  from operator import methodcaller
  import numpy
  import pytest
  import pandas
  from pandas import DataFrame, Index, Series, Timestamp
  import pandas._testing
  from pandas.core.groupby.grouper import Grouper
  from pandas.core.indexes.datetimes import date_range
label_desc: Use image node_id 5 for calling a global function with example usage: test_apply_iteration() and returns: unknown