# Buggy code
def func(df, other, apply_func, call_queue_df=None, call_queue_other=None):
    if call_queue_df is not None and len(call_queue_df) > 0:
        for call, kwargs in call_queue_df:
            if isinstance(call, ray.ObjectID):
                call = ray.get(call)
            if isinstance(kwargs, ray.ObjectID):
                kwargs = ray.get(kwargs)
            df = call(df, **kwargs)
    if call_queue_other is not None and len(call_queue_other) > 0:
        for call, kwargs in call_queue_other:
            if isinstance(call, ray.ObjectID):
                call = ray.get(call)
            if isinstance(kwargs, ray.ObjectID):
                kwargs = ray.get(kwargs)
            other = call(other, **kwargs)
    return apply_func(df, other)


# Traceback (AttributeError)
import modin.pandas as pd
import glob

files = glob.glob('/path/to/files/*.parquet')
df = pd.concat([pd.read_parquet(file) for file in files])
df.reset_index(inplace=True)
df.drop(columns=['index', 'DATE', 'STATUS', 'ID', 'ID2],inplace=True)

df.groupby(['REPORTING_DATE', 'ENTITY', 'CURRENCY']).sum()

UserWarning: Multi-column groupby is a new feature. Please report any bugs/issues to bug_reports@modin.org.
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-15-081b1819b7d6> in <module>
----> 1 df.groupby(['DATA_SALDA', 'BANK', 'WALUTA_KON']).sum()

~/eksperyment/lib64/python3.6/site-packages/modin/pandas/groupby.py in sum(self, **kwargs)
323
324     def sum(self, **kwargs):
--> 325         return self._groupby_reduce(lambda df: df.sum(**kwargs), None)
326
327     def describe(self, **kwargs):

~/eksperyment/lib64/python3.6/site-packages/modin/pandas/groupby.py in _groupby_reduce(self, map_func, reduce_func, drop, numeric_only, **kwargs)
479                 reduce_args=kwargs,
480                 numeric_only=numeric_only,
--> 481                 drop=self._drop,
482             )
483         )

~/eksperyment/lib64/python3.6/site-packages/modin/backends/pandas/query_compiler.py in groupby_reduce(self, by, axis, groupby_args, map_func, map_args, reduce_func, reduce_args, numeric_only, drop)
1236             _reduce,
1237             new_columns=new_columns,
-> 1238             new_index=new_index,
1239         )
1240         result = self.__constructor__(new_modin_frame)

~/eksperyment/lib64/python3.6/site-packages/modin/engines/base/frame/data.py in groupby_reduce(self, axis, by, map_func, reduce_func, new_index, new_columns)
1148         """
1149         new_partitions = self._frame_mgr_cls.groupby_reduce(
-> 1150             axis, self._partitions, by._partitions, map_func, reduce_func
1151         )
1152         if new_columns is None:

~/eksperyment/lib64/python3.6/site-packages/modin/engines/base/frame/partition_manager.py in groupby_reduce(cls, axis, partitions, by, map_func, reduce_func)
66         if len(by_parts.shape) == 0:
67             by_parts = np.array([by_parts.item()])
---> 68         [obj.drain_call_queue() for obj in by_parts]
69         new_partitions = np.array(
70             [

~/eksperyment/lib64/python3.6/site-packages/modin/engines/base/frame/partition_manager.py in <listcomp>(.0)
66         if len(by_parts.shape) == 0:
67             by_parts = np.array([by_parts.item()])
---> 68         [obj.drain_call_queue() for obj in by_parts]
69         new_partitions = np.array(
70             [

AttributeError: 'numpy.ndarray' object has no attribute 'drain_call_queue'

# Fixed code
def func(df, apply_func, call_queue_df=None, call_queues_other=None, *others):
    if call_queue_df is not None and len(call_queue_df) > 0:
        for call, kwargs in call_queue_df:
            if isinstance(call, ray.ObjectID):
                call = ray.get(call)
            if isinstance(kwargs, ray.ObjectID):
                kwargs = ray.get(kwargs)
            df = call(df, **kwargs)
    new_others = np.empty(shape=len(others), dtype=object)
    for i, call_queue_other in enumerate(call_queues_other):
        other = others[i]
        if call_queue_other is not None and len(call_queue_other) > 0:
            for call, kwargs in call_queue_other:
                if isinstance(call, ray.ObjectID):
                    call = ray.get(call)
                if isinstance(kwargs, ray.ObjectID):
                    kwargs = ray.get(kwargs)
                other = call(other, **kwargs)
        new_others[i] = other
    return apply_func(df, new_others)