code: def test_apply_in_pandas_returning_column_names_sometimes(self):
      def merge_pandas(lft, rgt):
          res = pd.merge(lft, rgt, on=["id", "k"])
          if 0 in lft["id"] and lft["id"][0] % 2 == 0:
              return res
          res.columns = range(res.columns.size)
          return res
  
      self._test_merge(fn=merge_pandas)
  
imports: import unittest
  from typing import cast
  from pyspark.sql.functions import array, explode, col, lit, udf, pandas_udf, sum
  from pyspark.sql.types import ArrayType, DoubleType, LongType, StructType, StructField, YearMonthIntervalType, Row
  from pyspark.sql.window import Window
  from pyspark.errors import IllegalArgumentException, PythonException
  from pyspark.testing.sqlutils import ReusedSQLTestCase, have_pandas, have_pyarrow, pandas_requirement_message, pyarrow_requirement_message
  from pyspark.testing.utils import QuietTest
label_desc: Use image node_id 16 for calling the CogroupedApplyInPandasTestsMixin obj's underlying member method code with example usage: obj.test_apply_in_pandas_returning_column_names_sometimes() and returns: res, res