# Buggy code
def _reduce(df):
    other_len = len(df.index.names)
    df = df.reset_index(drop=False)
    # See note above about setting `as_index`
    groupby_args["as_index"] = as_index
    if other_len > 1:
        by_part = list(df.columns[0:other_len])
    else:
        by_part = df.columns[0]
    result = reduce_func(
        df.groupby(by=by_part, axis=axis, **groupby_args), **reduce_args
    )
    if (
        not isinstance(result.index, pandas.MultiIndex)
        and result.index.name is not None
        and "_modin_groupby_" in result.index.name
    ):
        result.index.name = result.index.name[len("_modin_groupby_") :]
    # Avoid inserting data after the first partition or if the data did not come
    # from this query compiler.
    if not as_index and (first_column not in df.columns or drop_by):
        return result.drop(columns=by_part)
    return result


# Traceback (ray.exceptions.RayTaskError)
Traceback (most recent call last):
File "groupby_test16.py", line 29, in <module>
df1 = gb.prod()
File "/localdisk/gashiman/modin/modin/pandas/groupby.py", line 333, in prod
return self._groupby_reduce(callable, None)
File "/localdisk/gashiman/modin/modin/pandas/groupby.py", line 582, in _groupby_reduce
query_compiler=groupby_qc.groupby_reduce(
File "/localdisk/gashiman/modin/modin/backends/pandas/query_compiler.py", line 1298, in groupby_reduce
new_modin_frame = qc._modin_frame.groupby_reduce(
File "/localdisk/gashiman/modin/modin/engines/base/frame/data.py", line 1259, in groupby_reduce
new_index = self._frame_mgr_cls.get_indices(
File "/localdisk/gashiman/modin/modin/engines/ray/pandas_on_ray/frame/partition_manager.py", line 87, in get_indices
new_idx = ray.get(new_idx)
File "/nfs/site/home/gashiman/.local/lib/python3.8/site-packages/ray/worker.py", line 1515, in get
raise value.as_instanceof_cause()
ray.exceptions.RayTaskError(ValueError): ray::modin.engines.ray.pandas_on_ray.frame.partition.deploy_ray_func() (pid=2588931, ip=10.241.129.19)
File "python/ray/_raylet.pyx", line 427, in ray._raylet.execute_task
File "python/ray/_raylet.pyx", line 449, in ray._raylet.execute_task
ray.exceptions.RayTaskError: ray::modin.engines.ray.pandas_on_ray.frame.axis_partition.deploy_ray_func() (pid=2588931, ip=10.241.129.19)
File "python/ray/_raylet.pyx", line 427, in ray._raylet.execute_task
File "python/ray/_raylet.pyx", line 449, in ray._raylet.execute_task
ray.exceptions.RayTaskError: ray::modin.engines.ray.pandas_on_ray.frame.partition_manager.func() (pid=2588931, ip=10.241.129.19)
File "python/ray/_raylet.pyx", line 463, in ray._raylet.execute_task
File "/localdisk/gashiman/modin/modin/engines/ray/pandas_on_ray/frame/partition_manager.py", line 44, in func
return apply_func(df, other)
File "/localdisk/gashiman/modin/modin/backends/pandas/query_compiler.py", line 1248, in _map
result = map_func(
File "/localdisk/gashiman/modin/modin/pandas/groupby.py", line 332, in callable
return df.prod(**kwargs)
File "/nfs/site/home/gashiman/.local/lib/python3.8/site-packages/pandas/core/groupby/groupby.py", line 1371, in f
return self._cython_agg_general(alias, alt=npfunc, **kwargs)
File "/nfs/site/home/gashiman/.local/lib/python3.8/site-packages/pandas/core/groupby/generic.py", line 993, in _cython_agg_general
agg_blocks, agg_items = self._cython_agg_blocks(
File "/nfs/site/home/gashiman/.local/lib/python3.8/site-packages/pandas/core/groupby/generic.py", line 1022, in _cython_agg_blocks
result, _ = self.grouper.aggregate(
File "/nfs/site/home/gashiman/.local/lib/python3.8/site-packages/pandas/core/groupby/ops.py", line 586, in aggregate
return self._cython_operation(
File "/nfs/site/home/gashiman/.local/lib/python3.8/site-packages/pandas/core/groupby/ops.py", line 529, in _cython_operation
result = self._aggregate(
File "/nfs/site/home/gashiman/.local/lib/python3.8/site-packages/pandas/core/groupby/ops.py", line 608, in _aggregate
agg_func(result, counts, values, comp_ids, min_count)
File "pandas/_libs/groupby.pyx", line 511, in pandas._libs.groupby._group_prod
File "stringsource", line 658, in View.MemoryView.memoryview_cwrapper
File "stringsource", line 349, in View.MemoryView.memoryview.__cinit__
ValueError: buffer source array is read-only

# Fixed code
def _reduce(df):
    def compute_reduce(df):
        other_len = len(df.index.names)
        df = df.reset_index(drop=False)
        # See note above about setting `as_index`
        groupby_args["as_index"] = as_index
        if other_len > 1:
            by_part = list(df.columns[0:other_len])
        else:
            by_part = df.columns[0]
        result = reduce_func(
            df.groupby(by=by_part, axis=axis, **groupby_args), **reduce_args
        )
        if (
            not isinstance(result.index, pandas.MultiIndex)
            and result.index.name is not None
            and "_modin_groupby_" in result.index.name
        ):
            result.index.name = result.index.name[len("_modin_groupby_") :]
        if isinstance(by_part, str) and by_part in result.columns:
            if "_modin_groupby_" in by_part and drop:
                col_name = by_part[len("_modin_groupby_") :]
                new_result = result.drop(columns=col_name)
                new_result.columns = [
                    col_name if "_modin_groupby_" in c else c
                    for c in new_result.columns
                ]
                return new_result
            else:
                return result.drop(columns=by_part)
        return result

    try:
        return compute_reduce(df)
    # This will happen with Arrow buffer read-only errors. We don't want to copy
    # all the time, so this will try to fast-path the code first.
    except ValueError:
        return compute_reduce(df.copy())